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Computer Application

This book is a part of the course by Jaipur National University, Jaipur.This book contains the course content for Computer Application.

JNU, JaipurFirst Edition 2013

The content in the book is copyright of JNU. All rights reserved.No part of the content may in any form or by any electronic, mechanical, photocopying, recording, or any other means be reproduced, stored in a retrieval system or be broadcast or transmitted without the prior permission of the publisher.

JNU makes reasonable endeavours to ensure content is current and accurate. JNU reserves the right to alter the content whenever the need arises, and to vary it at any time without prior notice.

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Index

ContentI. ...................................................................... II

List of FiguresII. ....................................................... VII

List of TablesIII. .......................................................VIII

AbbreviationsIV. ........................................................IX

ApplicationV. ..............................................................111

BibliographyVI. ........................................................ 117

Self Assessment AnswersVII. ................................... 120

Book at a Glance

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Contents

Chapter I ....................................................................................................................................................... 1Introduction to Computers ......................................................................................................................... 1Aim ................................................................................................................................................................ 1Objectives ...................................................................................................................................................... 1Learning outcome .......................................................................................................................................... 11.1 Computers Everywhere ............................................................................................................................ 21.2 History and Evolution .............................................................................................................................. 21.3 Classification ............................................................................................................................................ 3 1.3.1 Definitions, Concepts and Features ......................................................................................... 31.4 Data Representation ................................................................................................................................. 41.5 Error Detecting Codes .............................................................................................................................. 5Summary ....................................................................................................................................................... 6References ..................................................................................................................................................... 6Recommended Reading ............................................................................................................................... 6Self Assessment ............................................................................................................................................. 7

Chapter II ..................................................................................................................................................... 9Computer Components and Information Processing Cycle .................................................................... 9Aim ................................................................................................................................................................ 9Objectives ...................................................................................................................................................... 9Learning outcome .......................................................................................................................................... 92.1 Introduction ............................................................................................................................................ 102.2 Components ........................................................................................................................................... 102.3 Input Devices ......................................................................................................................................... 10 2.3.1 Keyboard ................................................................................................................................ 10 2.3.2 Pointing Devices .....................................................................................................................11 2.3.3 Pen Input Devices ...................................................................................................................11 2.3.4 Video Input Devices ................................................................................................................11 2.3.5 Audio Input Devices .............................................................................................................. 12 2.3.6 Graphic Capture Devices ....................................................................................................... 12 2.3.7 Code Numbers ....................................................................................................................... 12 2.3.8 Optical Input Devices ............................................................................................................ 132.4 Central Processing Unit ......................................................................................................................... 13 2.4.1 Arithmetic Logic Unit (ALU) ................................................................................................ 13 2.4.2 Control Unit (CU) .................................................................................................................. 14 2.4.3 Primary Memory .................................................................................................................... 142.5 Output Devices ....................................................................................................................................... 15 2.5.1 Visual Output Devices (Soft copy) ........................................................................................ 16 2.5.2 Audio Output Devices (Soft copy) ......................................................................................... 16 2.5.3 Hardcopy Devices (print and film) ........................................................................................ 17 2.5.4 Computer Output Microfilms (COM) .................................................................................... 172.6 Data Storage ........................................................................................................................................... 17 2.6.1 Auxiliary Storage/Secondary Storage .................................................................................... 17 2.6.2 Magnetic Disk ....................................................................................................................... 18 2.6.3 Magnetic Tapes ...................................................................................................................... 19 2.6.4 Optical Disks .......................................................................................................................... 19 2.6.5 Flash Memory ........................................................................................................................ 21 2.6.6 USB Drives ............................................................................................................................ 21 2.6.7 Removable Hard Drives ......................................................................................................... 21 2.6.8 Smart Cards ............................................................................................................................ 22 2.6.9 Optical Cards ......................................................................................................................... 22Summary ..................................................................................................................................................... 23References ................................................................................................................................................... 23Recommended Reading ............................................................................................................................. 23Self Assessment ........................................................................................................................................... 24

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Chapter III .................................................................................................................................................. 26Hardware and Software ............................................................................................................................ 26Aim .............................................................................................................................................................. 26Objectives .................................................................................................................................................... 26Learning outcome ........................................................................................................................................ 263.1 Introduction ........................................................................................................................................... 273.2 Hardware ................................................................................................................................................ 27 3.2.1 Motherboard ........................................................................................................................... 273.3 Software ................................................................................................................................................. 273.4 Programming Languages ....................................................................................................................... 28 3.4.1 Machine Language ................................................................................................................. 28 3.4.2 Assembly Language ............................................................................................................... 28 3.4.3 High Level Language ............................................................................................................. 28 3.4.4 Fourth Generation Language ................................................................................................. 28 3.4.5 Natural Language ................................................................................................................... 293.5 Systems Software ................................................................................................................................... 29 3.5.1 BIOS ...................................................................................................................................... 29 3.5.2 Operating System (OS) .......................................................................................................... 29 3.5.3 Utility Software ...................................................................................................................... 313.6 Application Software ............................................................................................................................. 31Summary ..................................................................................................................................................... 33References ................................................................................................................................................... 33Recommended Reading ............................................................................................................................. 33Self Assessment ........................................................................................................................................... 34

Chapter IV .................................................................................................................................................. 36Communication and Networks ................................................................................................................. 36Aim .............................................................................................................................................................. 36Objectives .................................................................................................................................................... 36Learning outcome ........................................................................................................................................ 364.1 Introduction ............................................................................................................................................ 374.2 Computer Networks ............................................................................................................................... 374.3 Goals of Networks ................................................................................................................................. 374.4 Communication Channels ...................................................................................................................... 37 4.4.1 Wired Channels (Twisted-pair Wire, Coaxial Cable and Fibre-optic Cable) ......................... 38 4.4.2 Wireless Channels (Radio Link, Microwave Link, Satellite Communication) ..................... 394.5 Transmission Technology ...................................................................................................................... 40 4.5.1 Broadcast Networks .............................................................................................................. 40 4.5.2 Point-to-Point or Switched Networks ................................................................................... 41 4.5.3 Bandwidth .............................................................................................................................. 414.6 Network Configuration .......................................................................................................................... 42 4.6.1 Client-Server Network ........................................................................................................... 42 4.6.2 Peer-to-peer Network ............................................................................................................. 424.7 Network Models ..................................................................................................................................... 42 4.7.1 OSI Reference Model ............................................................................................................ 42 4.7.2 TCP/IP Protocol ..................................................................................................................... 454.8 Network Topologies ............................................................................................................................... 454.9 Types of Networks ................................................................................................................................. 49Summary ..................................................................................................................................................... 51References ................................................................................................................................................... 51Recommended Reading ............................................................................................................................. 51Self Assessment ........................................................................................................................................... 52

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Chapter V .................................................................................................................................................... 54Data processing .......................................................................................................................................... 54Aim .............................................................................................................................................................. 54Objectives .................................................................................................................................................... 54Learning outcome ........................................................................................................................................ 545.1 Introduction ............................................................................................................................................ 55 5.1.1 Data ........................................................................................................................................ 56 5.1.2 Information ............................................................................................................................ 56 5.1.3 Types of Data ......................................................................................................................... 565.2 Input, Processing and output .................................................................................................................. 56 5.2.1 Input ....................................................................................................................................... 56 5.2.2 Processing .............................................................................................................................. 57 5.2.3 Output .................................................................................................................................... 575.3 Architecture of Computer System .......................................................................................................... 57 5.3.1 The Control Unit (CU) ........................................................................................................... 57 5.3.2 The Immediate Access Store (IAS)........................................................................................ 58 5.3.3 ALU stands for Arithmetic and Logic Unit. .......................................................................... 585.4 Concepts of Files .................................................................................................................................... 58 5.4.1 File contents ........................................................................................................................... 58 5.4.2 Operations on the file ............................................................................................................. 59 5.4.3 File Organisation .................................................................................................................... 59 5.4.4 Relative File ........................................................................................................................... 60 5.4.5 Indexed Files .......................................................................................................................... 615.5 Protecting Files ...................................................................................................................................... 625.6 Storing files ............................................................................................................................................ 62 5.6.1 Backing up files ..................................................................................................................... 625.7 File Terminology .................................................................................................................................... 63 5.7.1 Records .................................................................................................................................. 63 5.7.2 Fields ...................................................................................................................................... 645.8 Data Capturing ....................................................................................................................................... 64 5.8.1 Direct Data Capturing ............................................................................................................ 64 5.8.2 Data Capture Forms ............................................................................................................... 655.9 Verification ............................................................................................................................................. 66 5.9.1 Editing and Checking ............................................................................................................. 67Summary ..................................................................................................................................................... 69References ................................................................................................................................................... 69Recommended Reading ............................................................................................................................. 70Self Assessment ........................................................................................................................................... 71

Chapter VI .................................................................................................................................................. 73Operating Systems ..................................................................................................................................... 73Aim .............................................................................................................................................................. 73Objectives .................................................................................................................................................... 73Learning outcome ........................................................................................................................................ 736.1 Introduction ............................................................................................................................................ 746.2 Operating System ................................................................................................................................... 74 6.2.1 Functions of Operating System .............................................................................................. 74 6.2.2 Operating System as User Interface ....................................................................................... 746.3 History of Operating System ................................................................................................................. 766.4 Disk Operating System ......................................................................................................................... 76 6.4.1 History of DOS ..................................................................................................................... 76 6.4.2 Components of MS-DOS ....................................................................................................... 76 6.4.3 Internal Command ................................................................................................................. 77 6.4.4 External Commands ............................................................................................................... 806.5 UNIX ...................................................................................................................................................... 82

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6.5.1 MEM ...................................................................................................................................... 82 6.5.2 FILTER .................................................................................................................................. 83 6.5.3 ATTRIB .................................................................................................................................. 84 6.5.4 DELTREE .............................................................................................................................. 84 6.5.5 EDIT ...................................................................................................................................... 846.6 Batch Files ............................................................................................................................................. 846.7 Batch System ......................................................................................................................................... 856.8 Time Sharing Systems............................................................................................................................ 866.9 Multiprogramming ................................................................................................................................. 876.10 Spooling ............................................................................................................................................... 886.11 Essential Properties of the Operating System Batch ............................................................................ 88 6.11.1 Time Sharing ........................................................................................................................ 88 6.11.2 Interactive ............................................................................................................................ 88 6.11.3 Real time system .................................................................................................................. 89 6.11.4 Distributed ............................................................................................................................ 89Summary ..................................................................................................................................................... 90References ................................................................................................................................................... 90Recommended Reading ............................................................................................................................. 91Self Assessment ........................................................................................................................................... 92

Chapter VII ................................................................................................................................................ 94Internet and Network Security ................................................................................................................. 94Aim .............................................................................................................................................................. 94Objectives .................................................................................................................................................... 94Learning outcome ........................................................................................................................................ 947.1 Internet ................................................................................................................................................... 957.2 Internet Architecture .............................................................................................................................. 95 7.2.1 Protocol .................................................................................................................................. 95 7.2.2 IP Address ............................................................................................................................. 95 7.2.3 Domain Name Service ........................................................................................................... 95 7.2.4 Packet Switching .................................................................................................................... 95 7.2.5 Internet Routers ...................................................................................................................... 96 7.2.6 Backbones .............................................................................................................................. 967.3 Network Security ................................................................................................................................... 96 7.3.1 Understanding Potential Threats ............................................................................................ 96 7.3.2 Steps towards Security ........................................................................................................... 977.4 Uses of Internet ...................................................................................................................................... 98Summary ..................................................................................................................................................... 99References ................................................................................................................................................... 99Recommended Reading ............................................................................................................................ 99Self Assessment ......................................................................................................................................... 100

Chapter VIII ............................................................................................................................................. 102World Wide Web ...................................................................................................................................... 102Aim ............................................................................................................................................................ 102Objectives .................................................................................................................................................. 102Learning outcome ...................................................................................................................................... 1028.1 Introduction .......................................................................................................................................... 1038.2 Functioning of the WWW .................................................................................................................... 103 8.2.1 Web Page.............................................................................................................................. 104 8.2.2 URL ...................................................................................................................................... 104 8.2.3 Web Server .......................................................................................................................... 104 8.2.4 HTTP .................................................................................................................................... 104 8.2.5 HTML .................................................................................................................................. 1048.3 Using the WWW .................................................................................................................................. 105

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8.3.1 Web Browser ........................................................................................................................ 105 8.3.2 Searching for Information ................................................................................................... 105 8.3.3 Search Techniques ............................................................................................................... 1058.4 Advanced Application: Emergence of Web 2.0 ................................................................................... 106Summary ................................................................................................................................................... 108References ................................................................................................................................................. 108Recommended Reading ........................................................................................................................... 108Self Assessment ......................................................................................................................................... 109

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List of Figures

Fig. 2.1 Schematic representation of a computer system ............................................................................ 10Fig. 2.2 Disk sectors..................................................................................................................................... 18Fig. 2.3 Track sectors ................................................................................................................................... 18Fig. 2.4 Logical layout of magnetic disk ..................................................................................................... 19Fig. 4.1 OSI reference model ....................................................................................................................... 43Fig. 4.2 Bus topology ................................................................................................................................... 46Fig. 4.3 Star topology................................................................................................................................... 47Fig. 4.4 Ring topology ................................................................................................................................. 47Fig. 4.5 Tree topology .................................................................................................................................. 48Fig. 4.6 Mesh topology ................................................................................................................................ 49Fig. 5.1 Block diagram of CPU ................................................................................................................... 57Fig. 5.2 Relative File - Organisation ............................................................................................................ 60Fig. 5.3 Files and folders arranged in a hierarchy ........................................................................................ 61Fig. 5.4 Sample data capture form ............................................................................................................... 66Fig. 5.5 Form filled by the customer ............................................................................................................ 66Fig. 6.1 Conceptual view of a computer system .......................................................................................... 75Fig. 6.2 Memory layout for a simple batch system ...................................................................................... 85Fig. 6.3 Memory layout for a multiprogramming system ............................................................................ 87Fig. 6.4 Spooling .......................................................................................................................................... 88Fig. 8.1 Basic hypertext enhanced by searches .......................................................................................... 103

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List of Tables

Table 1.1 Computer evolution ........................................................................................................................ 3Table 4.1 Types of networks ........................................................................................................................ 50Table 5.1 Types of Data ............................................................................................................................... 56Table 5.2 File terminology ........................................................................................................................... 63Table 5.3 Records ......................................................................................................................................... 63Table 5.4 Fields ............................................................................................................................................ 64Table 5.5 Types of validation ....................................................................................................................... 68Table 6.1 History of OS ............................................................................................................................... 76Table 6.2 Some Special $ Parameters Are Given Below ............................................................................. 80Table 7.1 Types of threats and consequences............................................................................................... 96

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Abbreviations

ALU - Arithmetic Logic Unit ARPA - Advanced Research Project Agency ASCII - American Standard Code for Information InterchangeBIOS - Basic Input Output System BPS - Bits Per Second CD - Compact Disk COM - Computer Output Microfilms CPU - Central Processing Unit CRT - Cathode Ray Tube Displays CU - Control Unit DNS - Domain Name System DPI - Dots Per InchDRAM - Dynamic RAM DTP - Desktop Publishing DVD - Digital Video Device or Digital Versatile DeviceEDO RAM - Enhanced Data Output DRAM EEPROM - Electronically Erasable PROM EHF - Extremely High Frequency EPROM - Erasable PROM Gbps - Gigabits Per Second GUI - Graphical User InterfaceHTML - Hyper Text Markup Language HTTP - The Hypertext Transfer Protocol I/O - Input/OutputIAS - Immediate Access Storage ICC - Integrated Circuit Card ISCII - Indian Standard Code for Information InterchangeISO - International Standards Organisation LAN - Local Area NetworkLCD - Liquid Crystal Display LED - Light Emitted DiodeLLC - Logical Link Control MAC - Media Access Control MAN - Metropolitan Area Network MICR - Magnetic Ink Character Recognition MIDI - Musical Instrument Digital Interface NSF - National Science Foundation OC - Optical CarrierOCR - Optical Character Readers OMR - Optical Mark Readers OS - Operating System OSI - Open System Interconnection PCB - Printed Circuit Board PDAs - Personal Digital AssistantsPIMs - Personal Information ManagersPROM - Programmable ROM RAM - Random Access MemoryRDRAM - RAM bus DRAM ROM - Read Only Memory SDRAM - Synchronous DRAM SHF - Super-high frequency

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SRAM - Static RAM STP - Shielded Twisted Pair TCP/IP - Transmission Control Protocol/Internet ProtocolURI - Uniform Resource Identifier URL - Uniform Resource Locator UTP - Unshielded Twisted Pair VDT - Visual Display Terminals VLF - Very Low Frequency WAN - Wide Area Network WORM - Write Once Read Many WWW - World Wide WebWYSIWYG - What You See Is What You Get

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Chapter I

Introduction to Computers

Aim

The aim of the chapter is to:

explain the concepts and features of computers•

elucidate ‘data representation’•

explicate the significance of computers in daily life•

Objectives

The objectives of the chapter are to:

explain important stages of computer evolution•

determine the method of data representation, and its standardisation•

enlist error-detecting methods•

Learning outcome

After end of this chapter, you will be able to:

identify characteristics and features of computer•

understand the method of data representation•

recognise error-detecting methods•


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1.1 Computers EverywhereComputers are showing up everywhere you look, and even in places you can't see. Computers check out your groceries, pump your gas, dispense money at the ATM, and turn the heat on and off, control the way your car runs. They are everywhere!

In fact, computer is rapidly becoming, if it hasn't already gotten there, as tightly woven into the fabric of our lives as the automobile. The analogy runs quite deep.

When automobiles were new, many people said "Those smelly, loud, complicated things will never replace the horse!" and "Those things break down in just a few miles, while my faithful horse goes on and on and repairs itself!" Nowadays it's hard to imagine the world without all the variety of four-wheeled, internal combustion vehicles. How many can you name? Sedans, pickup trucks, fire engines, front-end loaders, 4-wheelers, golf carts, bulldozers, cranes, vans, dump trucks and so on. We have an "automobile" for every purpose under heaven - and in different models and colours, too. So it is with computers. There are different kinds of computers for different purposes with variety in size, expense, and ability.

We can have a brief overview of how the computers we use today were developed and evolved to the current stage.

1.2 History and EvolutionHistorically, the word computer has been derived from the Latin word ‘computere,’ which means to calculate. Therefore, the term computer can logically be applied to any calculating device. The Abacus, the first “automatic” computer was invented in china as a first attempt at automating the counting process. Abacus is a machine which allows the user to remember his current state of calculations while performing more complex mathematical operation.

PioneersGottfried Leibniz Wilhelm, Blaise Pascal, Charles Babbage are the fore fathers of modern computers.

Blaise Pascal invented one of the first mechanical calculator: The Pascaline• Gottfried Leibniz Wilhelm invented the binary system which is the foundation of virtually all modern computer • architectures. It is used internally by modern computers. Made up of 0s and 1s, it is used for card readers, electric circuits, and vacuum tubes.Charles Babbage is credited with invention of the first mechanical computer, called the Difference Engine, • which eventually led to more complex and advanced designs. He originated the concept of a programmable computer.

Computer evolution as per the generations has been tabulated below:

Generation Years Switching device Storage device Software Applications

First 1949-55 Vacuum tubes Acoustic delay lines and later magnetic drum. I K byte memory

Machine and assembly languages. Simple monitors

Mostly scientific, later simple business systems

Second 1956-65 Transistors Magnetic core main memory, tapes and disk peripheral memory 100 Kbyte main memory

High level language. Fortran , Cobol, Algol batch operating system

Extensive business applications, engineering design optimisation

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Third 1966-75 Integrated circuits (IC)

High speed magnetic cores. Large disks (100 MB). IM byte main memory

Fortran IV, Cobol 68, PL/1, time shared operating system

Data base management systems, online systems

Fourth (first decade)

1975-84 Large scale integrated circuits, microprocessors

Semi conductor memory. Winchester disk. 10 M byte main memory 1000 M byte disks

Fortran 77, Pascal, Cobol 74

Personal computers, Integrated CAD/CAM. Real time control. Graphics oriented systems

Fourth generation (second decade)

1985-91 Very large scale IC. Over 3 million transistors per chip

Semiconductor memory. 1 GB main memory. 100 GB disk

C, C++ Java, Prolog

Simulation, visualisation, parallel computing multimedia

Fifth generation

1991-present

Parallel computing and superconductors

Attachable hard drives, USB drives used to add memory

Use of artificial intelligence

Voice recognition and response to natural language

Table 1.1 Computer evolution

1.3 ClassificationEarlier, computers were classified as microcomputers, minicomputers, super minicomputers, main frames computers and supercomputers. Due to technological advances, this classification is irrelevant in today’s time.

Now, all computers use microprocessors. Based on the mode of use, they can be classified as palmtop, laptop, desktop and work station.

1.3.1 Definitions, Concepts and FeaturesA computer is an electronic device that executes the instructions in a program. A computer has four functions:

Input Accepts data

Processing Processes data

Output Produces output

Storage Stores results

The computer is omnipresent mainly for following features:Speed: A computer can do billions of actions per second. �Reliability: Failures are usually due to human error, one way or another. �Storage: A computer can store huge amounts of data. �

In technical parlance, the term computer refers specifically to an electronic computer. Virtually all computers are • “digital” because they are composed of digital (electronic) circuits built with microscopic transistors. Therefore, they can only process digital data (discrete electronic signals). Most “real world” data is “analog” (continuous electronic signals, e.g. light, sound, movement and so on). • Therefore, it must be converted to digital (A/D conversion) when encoded and vice versa (D/A conversion) when being decoded.


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Based on the above features, we can • define a computer as essentially, an electronic device that can receive and store data and perform a set of instructions called programs. The computers act upon these programs in a pre-determined and predictable fashion to process the data in a desired manner.

The following words are so basic to computers that it is virtually impossible to talk about computers without using them. Therefore, below are some preliminary definitions and details shall be covered later:

Computer: It is an electronic machine that processes data (digital) into human information (numeric, text, or • physical) or controls electrical devices.Microcomputer: Computer based on a microprocessor• Computer System: Hardware, software, data and procedures for using the system• Hardware: Physical equipment of a computer system• Software: Program that are installed and “run” on the computer• Firmware: Software that is permanently stored in a computer’s read only memory• Program: Set of step-by-step instructions, in a computer language, that commands a computer to execute a • specific task in finite time.

1.4 Data RepresentationThe characters and numbers fed to a computer and the output from the computer must be in a form readable and usable by the people. For this purpose, natural language symbols and decimal digits are appropriate. These constitute the external data representation. On the other hand, the representation of data inside a computer must match the technology used by the computer to store and process data. All data to be stored and processed in computers are transformed or coded as strings of two symbols, one symbol to represent each state.

The two symbols used are 0 and 1. These are known as • Binary digits or bits, an abbreviation for data representation.

There are 4 unique combinations of two bits: 00 01 10 11

There are 8 unique combinations or strings of 3 bits each: 000 001 010 011 100 101 110 111

Each unique string of bits may be used to represent or code a symbol. In order to code the 26 capital letters of • English, at least 26 unique strings of bits are needed. Five bits are sufficient as 32 strings of 5 bits each can be formed.Coding of characters has been standardised to facilitate exchange of recorded data between computers. The • most popular standard is known as ASCII (American Standard Code for Information Interchange). This uses 7 bits to code each character. Besides codes for characters, in this standard, codes are defined to convey information such as end of line, end • of page and so on.In addition to ASCII, another code known as ISCII (Indian Standard Code for Information Interchange) has • been standardised by the Indian Standards Organisation. It is an eight bit code which allows English and Indian script alphabets to be used simultaneously.A string of bits used to represent a character is known as byte. Characters coded in ISCII need 8 bits for each • character. The byte is commonly understood as a string of 8 bits.

Thus, 1 � bit = 0 or 1, on or off 1 � byte = 8 bits 1 � kilobyte (K or KB) = 1024 bytes 1 � megabyte (MB) = 1024 kilobytes

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You might wonder, why 1024 instead of 1000 bytes per kilobyte? That is because computers don't count by tens • like we do. Computers count by twos and powers of 2. Therefore, 1024 is 2 times itself ten times, i.e.

1024 is 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2

1.5 Error Detecting CodesErrors may occur in recording data on magnetic surfaces due to bad spots on the surface or because of electrical disturbances during data transmissions between units. The principle used to detect errors in codes is the introduction of an extra bit along with each character code. A common method is the use of parity check bit. A parity check bit is appended to the 7 bits of the code of each character in such a way that the total number of 1s in each character code is even.

For example, the ASCII code of the letter E is 1000101. The number of 1s in the string is odd. A parity check bit 1 is appended to this string to obtain a code which is now 8 bits long and has an even number of 1s in it. If the ASCII code of a character has already an even number of 1 s, then the parity check bit appended is 0. Whenever a character is read from storage or received from a remote location, the 1s in its code are counted. It has to be even, if it is odd, then at least one bit is wrong. A single error in any of the 8 bits of the code will definitely be detected.Two errors cannot be detected in this scheme. But as the probability of more than 1 error occurring in practice is small, this scheme is commonly accepted and is adequate. There are other error-detecting codes devised which can detect more than one errors, and also correct those errors.


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SummaryHistorically, the word computer has been derived from the Latin word ‘computere,’ which means to calculate. • Therefore, the term computer can logically be applied to any calculating device.The characters and numbers fed to a computer and the output from the computer must be in a form readable • and usable by the people.Errors may occur in recording data on magnetic surfaces due to bad spots on the surface or because of electrical • disturbances during data transmissions between unitsComputers are classified in to a number of generations based on the electronic technology used in constructing • the computer, and the associated system software and applications.As the physical devices used for storage and processing of data in computers are two-state devices, it is necessary • to transform or code all data using only two symbols.The American Standards Institution has evolved a standard code to represent characters to be stored and processed • by computers. The code is known as the ASCII code.Detection of errors during data processing is possible by adding an extra bit in the code. The bit appended to • the code is known as the parity check bit.

ReferencesShelly, B. G., Freund, M. S. & Vermaat, M., 2010. • Introduction to Computers, 8th ed. Cengage Learning.Joshi, R., 2006.• Introduction To Computers, Gyan Publishing House.Introduction to Computers• [Pdf] Available at: <http://220.227.161.86/20059ipcc_paper7A_vol1_cp1.pdf> [Accessed 27 May 2013].Introduction to Computers• [Pdf] Available at: <http://www.cengagesites.com/academic/assets/sites/5096/dc_chapter1.pdf> [Accessed 27 May 2013].History of Computers• [Video online] Available at: <http://www.youtube.com/watch?v=LvKxJ3bQRKE&list=PL4D468968D6E4AF6C> [Accessed 27 May 2013].Dakshinamurthi, K., 2013. • ClassificationofComputer [Video online] Available at: <http://www.youtube.com/watch?v=-yD3EtqnHwQ> [Accessed 27 May 2013]

Recommended ReadingVenkatachalam, S., 1996. • An Introduction to Computers, Pitambar Publishing.Gipp, J., 2008. S• potlight on Introduction to Computers, 2nd ed. Cengage Learning.Introduction to Computer Science• , 2/e, 2nd ed. Pearson Education India

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Self AssessmentThe first automatic computer was ____________,1.

Vacuum tubesa. Abacusb. Transistorsc. Mini computerd.

Match the following2. 1. Blaise Pascal A. The binary system

2. Gottfried Leibniz Wilhelm B. Difference engine

3. Charles Babbage C. Mechanical calculators1-C, 2-A, 3-Ba. 1-C, 2-B, 3-Ab. 1-A, 2-C, 3-Bc. 1-B, 2-A, 3-Cd.

The concept of programmable computers was originated by ____________.3. B Pascala. Gottfried Leibniz Wilhelmb. Charles Babbage:c. Ada Lovelace Byrond.

Use of integrated circuits as a switching device was started from which generation of computers?4. Third a. Secondb. Firstc. Fifthd.

Computers are classified as palmtop, laptop, desktop and work station based on ____________.5. operating systema. year of evolutionb. name of inventorc. mode of used.

Which of the following is not a feature of the computer?6. Speeda. Storageb. Economyc. Reliabilityd.

The two digits 0 and 1 used for data representation are known as ____________7. symbolsa. bitsb. bytesc. switchd.


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A string of bits used to represent a character is known as ____________.8. bita. codeb. bytec. circuitd.

American Standard Code for Information Interchange has helped: (State which is not TRUE)9. Standardise coding of charactersa. Facilitate in information exchangeb. Serve as an international standardc. Detect errorsd.

The common error detecting method is known as ____________10. mega bytea. parity check bitb. bitc. giga byted.

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Chapter II

Computer Components and Information Processing Cycle

Aim


explain the components of computer•

explicate the information processing cycle•

elucidate the secondary storage devices•

Objectives


expain the role of various input devices•

explicate important stages of computer processing in the CPU•

enlist various output devices•

Learning outcome


understand the features of central processing unit•

describe various types of output devices•

identify secondary storage devices•


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2.1 IntroductionThe first chapter described how data is represented for computers. Data in the form of binary digits is used by the computer to give desired results. But how does the computer receive and use the data, how it is processed, how are the results generated and conveyed?

To understand the information processing cycle of a computer, we first need to study about the parts or components of a computer.

2.2 ComponentsAs with most products, computers are designed in a variety of ways. There are, however, major similarities regardless of the brand (e.g. Dell, Gateway, IBM) of the computer. A computer system accepts data as an input: processes that data and provides data as output. During the processing the data must be stored. The processing is controlled by a sequence of instructions - the program - which is stored in the computer. The basic components of a computer system are therefore input devices, processor, backing storage devices and output devices. This fit together as depicted in the following figures as a schematic representation, as well as the actual representation of a computer.

Fig. 2.1 Schematic representation of a computer system (Source: http://www.egyankosh.ac.in/bitstream/123456789/985/1/Unit%201.pdf)

2.3 Input DevicesThe computer needs an input in some form to proceed with the next steps. Input and output devices are collectively called I/O devices. Input devices (and also output devices) are the hardware interfaces between the human user and computer system, but (as always) hardware is ‘driven’ by software, so when we talk about an I/O device, remember there is an associated ‘device driver.’

2.3.1 Keyboard

Keyboard is the most common data entry device having more than 100 keys on it. Almost all general-purpose • computers are supplied with a keyboard.When you press a key, a number (code) is sent to the computer to tell it which key you have pressed. Keyboards • are often used in conjunction with a screen on which the data entered are displayed. The keys on a keyboard are usually arranged in the same order as those on a typewriter. This layout of keys is called • QWERTY because Q-W-E-R-T-Y is the order in which the letters occur on the top row of the keyboard.

INPUTKeybord

Digitizer (e.g. mouse)Sorcon

OUTPUTVideo (Screen)

Audio (Speaker)Printer/Plotter

SECONDARY STORAGEDiskette, Hard Disk, Optical*

PRIMARY STORAGE(RAM and ROM) COMMUNICATIONS

Telecommunications (modem)Networks: Direct Connections

CONTROL UNIT (CU)

ARITMETIC LOGIC UNIT (ALU)

CPU

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Keyboards are widely used because they provide flexible method of data entry and can be used in most • applications. However, they do have limitations like entry using keyboard is a slow form of data entry process and is prone to error.

2.3.2 Pointing DevicesThese are also called Cursor Control Devices. Cursor Control Devices are used to place the cursor (a highlighted screen location indicating where the next action will occur), select menu items, and control the computer by ‘clicking buttons’ on the screen. If these are built into the computer they are called Integrated Pointing Devices. A few such devices available are:

Mouse: A standard device of GUI (Graphical User Interface). New versions are optic and have no moving parts. • An LED (Light Emitted Diode) records a reflected light which senses motion over a flat surface.Trackballs: Like an ‘upside-down mouse’: it has the advantage of being stationary.• Joysticks: A hand-held stick that pivots about one end indicating 360 degree directions.• Track point or pointing stick: A miniature joystick that responds to the touch of a single finger.• Track pads: A touch sensitive surface that translates finger motion into cursor motion.•

2.3.3 Pen Input DevicesThese are based on screens that sense the location of a special pen that is connected to the terminal. Following are some of the devices:

Light pens either detect the monitor’s light or emit light that can be picked up by a specially designed • monitor.Styluses are pens with electronic point heads which activate pixels on the monitor, usually a LCD display.• Handwriting recognition software translates alphanumeric to digitised equivalents: normally these needs to be • ‘trained’ to recognise an individual’s carefully printed letters, numbers, and symbols. These have been rather primitive, but significant advances have been made recently. They are the primary input device of hand-held PDAs (Personal Digital Assistants) and PIMs (Personal Information Managers) state –of-the- art readers reportedly are very accurate.Digitizing tablets are similar to light pens or styluses except one draws on a tablet rather than the screen. • Touch screen recognises human touch and allows selection of menu items displayed on a monitor by touching • them.

2.3.4 Video Input DevicesFollowing are the various video input devices:Digital cameras

Digital cameras have optics like regular photographic cameras: however, they record the single images • electronically (rather than on photographic film) in digital form. These images are stored in camera’s RAM (Random Access Memory), which like that in a computer is volatile. The images can be displayed immediately or stored on a secondary storage medium, e.g. a diskette, and processed • later using image processing software.

Digital video camerasThese are digital cameras which can store sequences of digital images on magnetic tape and play them back as • ‘movies.’ They are similar to camcorders, but camcorders store their images as analogue data. Digital video cameras are essential features of video conferencing where remote computers can actually control • a remote camera and remote users can share applications and collaborate on ‘whiteboards.’


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Analogue image convertersPhotographs taken with regular cameras and videos recorded with camcorders store their images as analogue • data. There are special kinds of hardware that can take these images (scanning photographs or converting camcorder • tapes) and convert them to digital images which, like any other digital image, can be processed by computers.

2.3.5 Audio Input DevicesFollowing are the various audio input devices:Digitized audio signals

Audio (analogue) signals can be converted to digital signals by analogue to digital converters, processed by a • computer and converted back with digital to analog converters. This allows computer manipulation of music (See MIDI, below), speech or any recordable sounds.Synthetic audio signals can be created by the computer. • Musical Instrument Digital Interface (MIDI) devices allow the input and output to any musical instrument • capable of electrical I/O. The music, once digitised in the computer’s memory can be processed by musical software giving incredible opportunities for creativity and innovation.

Voice input and speech recognitionMicrophones convert spoken words (analog signals) to digital signals that can be processed by a computer. • (Words are ‘digitised’)Digitized words are compared to ‘voice templates’ stored in memory.•

Customisable devices can be ‘trained’ to recognise an individual’s speech �Current systems are still rather primitive and have limited vocabularies: however, rapid developments are �being reported.

If a word is recognised, it is processed: if not, then the user has to give a recognisable input.•

2.3.6 Graphic Capture DevicesImage scanners are popular examples of graphic capture devices. When a page of text already exists, like the page that you are reading now, it can be directly put into a computer using a scanner. Scanner can be used to input not only the texts, but also the photographs, drawings and so on. Image Scanners (Gray-scale or colour) digitize the pictures (which are analog data). The resulting bitmapped images (Each pixel has a collection of bits that define its colour) can be easily modified by graphics programs. The resolution of bitmapped images is measured in dpi, i.e., dots per inch.

2.3.7 Code NumbersBarcode readers

The bar code is a pattern of thick and thin bars divided by thick and thin spaces. Only the relative separations • and thickness of the bars are important. Barcodes can be printed in different sizes and colours. The barcode is read either by passing a light-pen over it • or by passing the bar code over a flatbed scanner. Barcodes are suitable for data input when all that is necessary is to identify an item, and the data input simply • comprises a code. The reading of the barcode records a transaction, and information is fed back to a computer database. Barcode • systems are easy to operate and have very low error rates.Occasionally, a scanner can read a barcode number incorrectly. A check digit is included in the barcode number • to reduce such incidents.

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Magnetic ink character recognition (MICR)This input device is widely used by banks to process the tremendous volume of checks being received by • them. This can be seen at the bottom of a check leaf, where some code numbers are written using a special ink that • contains magnetisable particles of iron oxide.

Magnetic stripe codeIt is a short length of magnetic tape which may be stuck on the surface of a tag, card or document. On plastic • cards such as credit cards, the stripe is usually sealed in. Stripes store data in the form of magnetic spots which represent the 1’s and 0’s of the ASCII code.•

Smart cardsThese have a memory store in the form of a very thin integrated circuit sealed into them.• These can be used to store data about a customer, which can be updated as transactions are made using the • card.

2.3.8 Optical Input DevicesFollowing are the optical input devices:Optical Character Readers (OCR)

This device is similar in concept to MICR. Characters in a special font are printed on a document, and the reader • scans the document for reflected light patterns, then translates those patterns into a pattern of electrical signals, which are passed to the computer store.

Optical Mark Readers (OMR)These are similar to OCR except that the reader recognises marks in appropriately positioned boxes rather than • characters. These are found in areas where responses are one out of a small number of alternatives and the volume of data • to be processed is large. One can notice the usage OMR in bank examinations.

2.4 Central Processing UnitThe data given as an input to the computer is then processed at the Central Processing Unit (CPU). It can be thought of as a collection of processing and storage units within an Arithmetic Logic Unit (ALU) and Control Unit (CU) that are linked internally and externally by busses which carry binary signals between. Higher the bandwidth or processing speed of CPU the faster the machine is.

2.4.1 Arithmetic Logic Unit (ALU)The Arithmetic Logic Unit (ALU), as the name indicates, performs all the arithmetic and logic operation. ALU consists of:

Accumulator: It is the main data register where all the intermediate results of a calculation are kept (accumulated) • until the final result is determined (which is then stored in memory).Data registers are supplemental storage registers that support the operations of the accumulator.• Computational circuits (e.g. a binary adder) performs mathematical operations.• Operational circuits that perform logic operations: Here, all math operations are performed in binary numbers • and all logic operations are performed using binary operations. Math operations include addition, subtraction, multiplication and division. Logical operations allow programs to contain repetition and selection, the two essential control structures of programming. Logical operations performed by ALU include comparing two quantities: keeping a counter and deciding the further route.


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2.4.2 Control Unit (CU)This unit controls the internal functioning of a computer and input/output units. The role of control unit in CPU is that of a ‘manager’ or ‘a traffic cop.’ In other words, it controls and co-ordinates all hardware operations. The components of CU (greatly oversimplified for illustrative purposes) are:

Decoders interpret program instructions (object code written in machine language).• Timer (or clock) sequences all CPU activities.• Logical gates and circuits distribute signals which activate various components of the CPU.• Program counter/register keeps track of the next instruction to be executed• Registers is a group of (usually) bistable devices that are used to store information like instructions, address • and so on, within a computer system for high-speed access.

Primary CU Functions of primary CU are:

Read and interpret machine language instructions• Control the transmission of data between ALU, registers, cashes, primary memory, and auxiliary memory• Control the sequence of execution of program instruction (i.e. govern branching, jumping around within a • program) which allows repetition and selectionDirect ALU as to what math or logic operations to perform.•

2.4.3 Primary Memory

Primary memory, also called main memory or internal memory, provides temporary storage of programs in • execution and the data being processed. It is known as Immediate Access Storage (IAS) as this is the portion of CPU which can be accessed directly. • From the hardware point of view, the primary memory is formed by a large number of basic units referred to as • ‘memory cells.’ Each memory cell is a device or an electronic circuit that has two or more stable states, which represents the binary numbers 0 (Zero) or 1 (One). The computer can retrieve any item of data or any instruction stored in primary memory at lightning speed. The • modern computer does this in a few nano seconds. Primary memory can be further grouped into Random Access Memory (RAM) and Read Only Memory (ROM). • Cache memory (small, fast RAM) is designed to hold frequently used data. Summary of the features of each as given below:

Random Access Memory (RAM)This memory allows writing as well as reading of data, unlike ROM on which data cannot be written. • It is a volatile storage because the contents of RAM are lost when the power (computer) is turned off. If you • want to store the data for later use, you have to transfer all the contents to a secondary storage device.

There are several types of RAM, the most popular of which include:Dynamic RAM (DRAM), although its name sounds sophisticated, is the oldest and simplest (and therefore �the slowest) type of RAM used today. The word ‘dynamic’ comes from the fact that it must be electronically ‘refreshed’ constantly in order to maintain the stored data.Static RAM (SRAM), unlike DRAM, does not need to be refreshed: its storage is fixed (as long as power �is supplied to the computer). This newer, more dependable, type of RAM is faster but more expensive than DRAM. SRAM is often used for cache memory.Enhanced Data Output DRAM (EDO RAM) is a type of RAM that improves the memory access time on faster �microprocessors such as the Intel Pentium. EDO RAM was initially optimised for the 66 MHz Pentium. Synchronous DRAM (SDRAM) is a new form of RAM that can be synchronised to the clock speed of the �computer, a powerful feature that optimises data access by the system buses.

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Ram bus DRAM (RDRAM) is Intel’s designated successor to SDRAM having an effective speed of 800 MHz �and a peak data transfer rate of 1.6 GBps. However, it has yet to prove itself, and there are several rivals, e.g. DDR SDRAM, that are slower but have 64b bus widths thus providing comparable transfer rates.

Read Only Memory (ROM)Another type of microcomputer memory is read only memory. Data is ‘burnt’ into the ROM chip at the time • of manufacturing. Unlike RAM, the data on the ROM is non-volatile, i.e. data is not lost when the computer is switched off. •

Following are the popular ROMs:Programmable ROM (PROM) can be programmed to record information using a facility known as a PROM- �programmer. Once the chip has been programmed, the recorded information cannot be changed. Erasable PROM (EPROM) is erased by shining ultraviolet light on the exposed chip. To write to or erase �from EPROM, one must use a PROM burner.Electronically Erasable PROM (EEPROM) is more convenient than EPROM, because it can be erased �electronically and can be written to in bytes.Flash Memory, a special type of EEPROM, can be erased and rewritten in multi-byte blocks rather than the �single bytes characteristic of EEPROM. Flash memory is most often used to hold control code such as the Basic Input/output System (BIOS) in a personal computer: these are often called ‘flash BIOS’.

Cache Memory (small, fast RAM)It is designed to hold frequently used data. In general, • Cache (high speed RAM that is configured to hold the most frequently used data) is used to improve system performance.Memory cache or CPU cache is a dedicated bank of high-speed RAM chips used to cache data from primary • memory. When data is read from primary memory, a block larger than immediately necessary is stored in the cache under • the assumption that the next data needed by a program will be located near the data being read: when that data is needed, it will then be waiting in the high speed cache. Memory Cache may be either built into the CPU (level 1, or L1, cache, e.g. Pentiums and PowerPCs) or contained • in separate chips (level 2, or L2, cache,).After the data received through the input devices is processed in the central processing unit, the data in the form • of result is dispatched through the output devices.

2.5 Output DevicesOutput devices are the means by which computer systems communicate with people. Output devices accept data from the processor and convert them into the required output format. The convenience of use of these devices and the quality of their results has a significant impact on the effectiveness of a computer system. In other words, output devices translate the data in the processor into a format that is suitable for people to use. Most ‘real world’ data is analogue, i.e. it consists of continuous signals like sounds, pictures, voltage and so forth.

However, computers can only process digital data (discrete signals): therefore, input usually involves analogue to digital conversion (A/D hardware) and output reverses the process using D/A converters. Output can be sub-classified as either direct (to/from I/O devices) or indirect (to/from secondary storage). Output can also be divided into another two kinds: hard copy output (paper, microfilm, etc.) provides a permanent record while soft copy output (visual, audio, tactile, or action) is transient. Action output facilitates control of electromechanical devices, e.g. robotics. For the sake of convenience, let us follow the given classification to discuss the output devices.


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2.5.1 Visual Output Devices (Soft copy)

Cathode Ray Tube Displays (CRTs)• These are the most commonly seen output device. The computer screen is made of CRTs. They are also �called monitors or visual display terminals (VDTs). Monitors look identical to a television screen. They produce fast and virtually costless output of �information.CRTs use faster scan technology to portray images as bitmapped graphics on a phosphorescent screen. �Electrons are fired at the screen and light up tiny dots of phosphor, which then glow for a short period of time. Each point is called a picture element or pixel. Since the phosphors glow momentarily, the electronic gun keeps on firing the electron beam at regular �intervals. This refreshing mechanism is measured in Hertz (Hz) or cycles per second. A low refresh rate leads to screen flicker. Monochrome monitors use one colour images (usually black) on a one colour background (usually white), �e.g. old mainframe monitors. These are now virtually obsolete in PCs.On the other hand, colour monitors use a triad of red, green, and blue phosphor dots which are stimulated �in varying degrees to produce a wide range of colours. Composite video monitors (like TVs) have one electron gun. However, composite video has lower resolutions �than RGB monitors. RGB monitors use three electron beams which give a higher resolution display. Virtually, all modern monitors are RGB.The quality of the screen display or its resolution depends on the number of pixels on the screen. Resolution �indicates the ability to show details: the more pixels per inch, the higher the resolution.

Bitmapped CRTs allows individual pixels to be addressed thereby producing greater screen control: this is • the origin of WYSIWYG (What You See Is What You Get) applications that can incorporate high resolution graphics (e.g. all modern PC monitors).On the other hand, old fashioned character-addressable CRTs only address or manipulate groups of pixels • (that form alphanumeric) and are inherently non-WYSIWYG and have crude graphics (e.g. mainframe and minicomputer monitors). Vector Graphics screens create images by the electron gun tracing between specified points on the screen rather • than scanning every row: they are limited to special types of graphics monitors.Flat Panel Display, first introduced in watches and clocks in 1970s, is a technology now applied to display • terminals. They eliminate flicker and radiation and minimise size problems of CRTs. Further, they are popular for their low energy consumption. However, the quality of the images is relatively poor. Hence, they are commonly used in portable devices because of compactness and low energy requirements.Liquid Crystal Display (LCD) is the most popular type, which has a thin layer of liquid crystal molecules divided • into small squares forming pixels that are held by two glass sheets. When power is applied to a square it turns opaque. LCDs used to come in limited size, brightness and clarity, but current technology has significantly improved. Gas-plasma displays give the best image (though low contrast), but they cannot be battery operated.• Project Display is a small sized screen of the displays discussed above. Project displays provides an enlarged • image and could be projected on a large screen. These systems can be connected directly to the processor and the output will be displayed on the large screens.

2.5.2 Audio Output Devices (Soft copy)

The audio output device converts the digital signals and gives the output in an audible format. • Speech synthesisers transform digital computer signals into voice output. The voice maybe choppy and unnatural, but it is easily understood. Audio output units have a varied application.Speech synthesizers use different methods of output. In the • word analysis method, entire digitised words from the computer’s vocabulary are combined under computer control, into digitised sentences and then converted to analogue output. This requires a huge amount of memory.

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In the • constructive synthesis method, the basic elements of speech, called ‘phonemes’ (only 40 in the English language) are used to construct speech output governed by timing, pitch and inflection controls. This has minimal memory requirements.

2.5.3 Hardcopy Devices (print and film)Printers and PlottersPrintersThese are used to print the output data on paper. Such output is referred to as printout or hard copy. Printers can be classified as follows, based on various characteristics:

Image Formation (measured in dpi):• Full character alphanumeric (no graphics) have a separate symbol on a ball, daisy wheels, thimble, band, �belt or chain mechanism.Dot-matrix alphanumeric and graphics are formed by patterns of dots from a single print head. �Raster scan images (alphanumeric/graphics), e.g. laser printers, are like copiers. �

Image Transfer• Impact printers transfer images by, the print head striking a ribbon like a typewriter. �Non-impact printers transfer images by heat (electro-thermal and thermal-transfer printers), electrostatic �charge (laser printers), or by ‘drawing’ with ink jets.

Number of characters printed at one time, measured in ppm (pages per minute):Serial (bi-directional) printers print one alphanumeric or graphics pixel at a time. �Chain printers transfer one line of alphanumeric or pixels at a time. �Page printers (laser printers) utilise a combination of raster scan and xerographic technologies to produce �one whole page at a time.

PlottersThough a few printers listed above are capable of producing graphics, there are a few special plotters exclusively to print a good quality drawing and graphs. There are two types of plotters:

Flatbed plotters have a drawing instrument (pen, ink-jet, electrostatic head, or heater element) that moves both • horizontally and vertically, under the control of input voltages, over a flat piece of stationary paper. Drum plotters have a drawing pen that move vertically, while the paper on a drum rotates under it.•

2.5.4 Computer Output Microfilms (COM)

Special computers can produce their output directly onto microfilm. In this way, vast amounts of data in human • readable form can be stored in a very small space without the need of large quantities of paper. The microfilm is read by using a special device which magnifies the text and pictures so that they can be seen • with naked eyes.

2.6 Data StorageStorage refers to the media and methods used to keep information available for later use. Some things will be needed right away while other won't be needed for extended periods of time. Therefore different methods of storage are appropriate for different uses. The RAM, ROM, earlier described as a part of CPU, is the main memory of a computer. Main memory keeps track of what is currently being processed. These memory chips are the fastest, but most expensive, type of storage. It is volatile, meaning that turning the power off erases all of the data.

2.6.1 Auxiliary Storage/Secondary StorageAuxiliary storage holds what is not currently being processed. This is the part that is ‘filed away’, but is readily available when needed. It is non-volatile, meaning that turning the power off does not erase it.


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The primary storage has already been discussed: the secondary storage devices are as follows.

2.6.2 Magnetic Disk

A magnetic disk is a circular platter of plastic, which is coated with magnetised material. One of the key • components of a magnetic disk is a conducting coil named as Head (Read-write head) which performs the job of reading and writing on the magnetic surface. The head remains stationary while the disk rotates below it for reading or writing operation. All magnetic disks are similarly formatted, or divided into areas called tracks, sectors and cylinders.• Disk sector is a wedge-shape piece of the disk, shown in grey. Each sector is numbered. •

Fig. 2.2 Disk sectors(Source: http://www.jegsworks.com/Lessons/lesson6/lesson6-3.htm)

Fig. 2.3 Track sectors(Source: http://www.jegsworks.com/Lessons/lesson6/lesson6-3.htm)

A track sector is the area of intersection of a track and a sector, shown in grey.• The head of disk is a small coil and reads or writes on the position of the disk rotating below it: therefore, the • data is stored in concentric set of rings called tracks. The width of a track is equal to the width of the head. To minimise the interference of magnetic fields and to minimise the errors of misalignment of head, the adjacent tracks are separated by inter track gaps. As we go towards the outer tracks, the size of a track increases but to simplify electronics same numbers of bits are stored on each track

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DiskPlatter

Inter Sector gapor Intra track gap

Intra track gap

Sector

Fig. 2.4 Logical layout of magnetic disk(Source: http://www.egyankosh.ac.in/bitstream/123456789/4831/1/unit%201.pdf)

Floppy disks and hard disks are commonly used types of magnetic disk. Several other kinds of removable • magnetic media are in use, such as the Zip disk. All of these have a much higher capacity than floppy disks, but each type of media requires its own drive.

Hard DisksThese consist of 1 or more metal platters which are sealed inside a case. The metal is one which is magnetic. • The hard disk is usually installed inside the computer's case, though there are removable and cartridge types, • also. Technically, a • hard drive controls the motion of the hard disks containing the data. Though, most people use ‘hard disk’ and ‘hard drive’ interchangeably.

Floppy DisksA floppy disk is made of a flexible thin sheet of plastic material with a magnetic coating and grooves arranged • in concentric circles with tracks. Disk is removable from the reading device attached to the computer and therefore provides unlimited storage • capacity. The floppy disks are available in two sizes - 5.25 inches and 3.5 inches with capacity ranging from 360 KB to • 1.44 MB per disk. However, use of floppy disks has completely stopped, due to the volatility and availability of other improved mediums.

2.6.3 Magnetic Tapes

Magnetic tapes are mounted on reels or a cartridge or a cassette of tape to store large volumes or backup data. • These are cheaper and since are removable from the drive, they provide unlimited storage capacity. Information • retrieval from tapes is sequential and not random. These are not suitable for on-line retrieval of data, since sequential searching will take long time. These are • convenient for archival storage, or for backup. The tapes are one of the earliest storage devices having low cost, low speed, portability.•

2.6.4 Optical DisksIn optical storage devices, the information is written using laser beam on a plastic coated disk which can store digital data as tiny pits etched in the surface.


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Characteristics of optical disksThey are formed of layers• Data is in a spiral groove, starting from the centre of disk• Data is in digital format (1s and 0s)• 1s and 0s are formed by how the disk absorbs or reflects light from the tiny laser beam.•

Working of optical disksAn optical disk is made up of polycarbonate (a plastic). The data is stored on a layer inside the polycarbonate. • A metal layer reflects the laser light back to a sensor.To read the data on a disk, laser light shines through the polycarbonate and hits the data layer. How the laser • light is reflected or absorbed is read as a 1 or 0 by the computer.In a Compact Disk (CD), the data layer is near the top of the disk, the label side.• In a DVD, the data layer is in the middle of the disk. A DVD can actually have data in two layers. It can access • the data from one side or from both sides. This is how a double-sided, double-layered DVD can hold 4 times the data that a single-sided, single-layered • DVD can.

Types of optical disksFollowing are the types of optical disksRead Only

The most common type of optical disk is the CD-ROM, which stands for Compact Disk Read Only Memory. • It looks just like an audio CD but the recording format is quite different. CD-ROM disks are used for storing computer software.DVD stands for Digital Video Device or Digital Versatile Device: DVDs are used for recording movies and • store large amounts of data.Write Once Read Many: The CDs and DVDs that are commercially produced are of the Write Once Read Many • (WORM) variety. They can't be changed once they are created. That is, they allow writing only once, while data may be read many times.The data layer is physically moulded into the polycarbonate. Pits (depressions) and lands (surfaces) form the • digital data. A metal coating (usually aluminium) reflects the laser light back to the sensor. Oxygen can seep into the disk, especially in high temperatures and high humidity. This corrodes the aluminium, making it too dull to reflect the laser correctly.CD-ROM and DVD-ROM disks are readable for many years, if stored in good condition.•

Write OnceThe optical disks that you can record on your own computer are CD-R, DVD-R, and DVD+R disks, and called • as writable or recordable disks. Here, the metal and data layers are separate and metal layer can be of gold, silver, or a silver alloy.• Gold layers are best because gold does not corrode. Naturally, the best is more expensive. Sulphur dioxide in • air can seep in and corrode silver over time.The data layer is an organic dye that the writing laser changes. Once the laser modifies the dye, it cannot be • changed again. Ultraviolet light and heat can degrade the organic dye.A writable disk is useful as a backup medium when long-term storage of data is required. It is less efficient for • data that changes often, since a new recording is required each time the changed data is saved.

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RewriteAn option for backup storage of changing data is • rewritable disks, i.e. CD-RW, DVD-RW, DVD+RW, DVD+RAM. The data layer for these disks uses a phase-changing metal alloy film. This film can be melted by the laser's heat • to level out the marks made by earlier data and then again the new data can be recorded with laser. We can erase and write on these disks as many as 1000 times, for CD-RW, and even 100,000 times for the • DVD-RW types.

Advantages of optical disksPhysical: An optical disk is much sturdier than tape or a floppy disk. It is physically harder to break or melt or • warp.Delicacy: It is not sensitive to being touched, though it can get too dirty or scratched to be read, but it can be • cleaned. Magnetic: It is entirely unaffected by magnetic fields. • Capacity: Optical disks hold a lot of data, especial the double-sided DVDs. • For software providers, an optical disk is a great way to store the software and data that they want to distribute • or sell.

Disadvantages of optical disksCost•

The cost of a CD-RW has dropped drastically in short period of time. �The cost of disks can add up, too. Recordable disks (one time only) are also getting cheaper. But we have �to be careful about the capacity and maximum recording speed. For commercial use, the read/write drives are quite cost effective. For personal use, they are available and �are cheap enough to use for data storage for everyone.

Duplication• It is not quite as easy or as fast to copy an optical disk as it is to copy files to a USB flash drive. You need �the software and hardware for writing disks

2.6.5 Flash Memory

Several different brands of removable storage cards, also called as memory cards, are available in the market. • These are solid state devices that read and write data electrically and not magnetically.Devices like digital cameras, mobile phones and the like. may use compact flash, smart media, memory stick • or another flash memory card.Laptops use PCMCIA cards, which are a type of flash memory. They are as solid as hard disks.•

2.6.6 USB Drives

It is also known as flash drive, jump drive, flash pen, key drive etc. • They can be plugged in to a USB port of computer, without any requirement of drivers.• The storage capacities vary from 8MB to 128GB or more.•

2.6.7 Removable Hard DrivesVarious types of special drives that compress data are available. Since they provide high storage capacity, they can be used for back up as well.


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2.6.8 Smart Cards

A smart card, chip card, or integrated circuit card (ICC) is any pocket-sized card with embedded integrated • circuits. There are two broad categories of ICCs. Memory cards containing only non-volatile memory storage components, • and perhaps dedicated security logic. Microprocessor cards containing volatile memory and microprocessor components. The card is made of plastic. The most common smart card applications are: credit cards, electronic cash, computer • security systems and so on.

2.6.9 Optical CardsThe material is comprised of several layers that react when a laser light is directed at them. The laser burns a tiny hole (2.25 microns in diameter) in the material which can then be sensed by a low power laser during the read cycle.

The presence or absence of the burn spot indicates a 1 or 0. Because the material is actually burned during the • write cycle, the media is a ‘Write Once Read Many’ type and the data is non volatile (not lost when power is removed).Optical cards hold on the order of 1,000x the amount of information as the typical smart card and the data, once • written, is permanent and cannot be erased or altered in any way. Optical cards, unlike smart cards, are also impervious to electric and magnetic fields and also to static electricity.

Thus, we now have a complete picture of what the computer consists of and how all the components work together as a process. The idea of how data is received, and how it is processed to give the desired outputs in a required format should be clear.

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SummaryThe core components of a computer are input devices, processor, backing storage devices and output devices.• Data to be processed by computer needs to be converted in a machine readable form which can be done using • various input devices listed.Input can be provided by using any of the options like keyboard, pointing devices, pen input devices, video and • audio input devices or graphical capture.This data is then processed at the CPU which comprises of the Arithmetic Logic Unit, Control Unit and the • Primary Memory, i.e. RAM, ROM and cache.The processed data can be obtained by various output devices. Options for output are visual output devices like • the monitor, audio output devices, hardcopies through printers and computer output micro filmsThe processed data can also be stored in various secondary storage devices. These storage devices are magnetic • disks, magnetic tapes, optical disks, flash memory, USB drives, smart cards, etc.Storage is useful for further reference and back up.•

ReferencesShelly, B. G. & Vermaat, E. M., 2009. • Discovering Computers: Living in a Digital World : Fundamentals, 6th ed. Cengage Learning.Shim, K. J., 2002. • Information Systems and Technology for the Noninformation Systems Executive: An Integrated Resource Management Guide for the 21st Century, CRC Press.Information Processing 10, 20, 30 Curriculum Guidelines• [Pdf] Available at: <http://www.edcentre.ca/resources/info10/currmain.pdf> [Accessed 28 May 2013].Computer Fundamentals and Troubleshooting• , [Pdf] Available at: <http://infosecawareness.in/downloads/handbooks/computer-fundamentals-and-troubleshooting.pdf> [Accessed 28 May 2013].Prof. Kumar, A., 208. • Lecture -1 Introduction to Computer Architecture [Video online] Available at: <http://www.youtube.com/watch?v=4TzMyXmzL8M> [Accessed 28 May 2013].Janossy, J., • Computer components [Video online] Available at: <http://www.youtube.com/watch?v=kZH3H7XIUuc> [Accessed 28 May 2013]

Recommended ReadingP. Norton, 2002. • Introduction To Computers (Sie), Tata McGraw-Hill Education.Shelly, B. G. & Vermaat, E. M., 2008. • Discovering Computers 2009, Cengage Learning.Shelly, B. G. & Vermaat, E. M., 2011. • Discovering Computers, Brief: Your Interactive Guide to the Digital World, Cengage Learning


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Self AssessmentThe layout of keys is called 1. QWERTY because

QWERTY is easy to typea. Q-W-E-R-T-Y is the order in which the letters occur on the top row of the keyboard.b. It is the name of the keyboardc. It is the basic design of keyboardd.

Immediate access storage is also known as ____________2. primary memorya. secondary memoryb. magnetic diskc. optical diskd.

Which is not a part of graphical capture type of input?3. Barcodea. Smart cardb. Digitizing tabletc. Optical character readersd.

Track balls, joysticks and track pads are all types of ____________ devices.4. pen a. converting b. signal c. pointingd.

Arithmetic logic unit does not constitute of ____________5. data registersa. decodersb. computational circuitsc. accumulatord.

Which of the following is not a type of RAM?6. DRAMa. SRAMb. DDRAMc. SDRAMd.

____________is a dedicated bank of high-speed RAM chips used to cache data from primary memory.7. RAMa. ROMb. Flash memoryc. Memory cached.

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Cathode ray tube display is also known as ____________8. monitora. logical gateb. computational circuitc. action outputd.

Which of the following is a volatile memory?9. Floppy diska. Optical diskb. Cache memoryc. Flash memoryd.

Which type of storage device uses electricity to write data?10. Hard diska. Flash memoryb. Floppy diskc. Magnetic tapesd.


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Chapter III

Hardware and Software

Aim


explain the types of hardware and software•

elucidate the concept of programmin language•

explicate systems software•

Objectives


determine the role of motherboard as an important hardware component•

explain the concept of system software and some important types•

explicate application software and its types•

Learning outcome

After end of this chapter, the students should be able to:

undertsand the concept of BIOS •

describe the functions of operating system•

identify the types of operating system•

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3.1 Introduction All physical contents of computer are hardware. This form is given to all electrical and mechanical devices attached to the computer for the purpose of input, process, and storage and output operations. Primary hardware is the CPU and its other units i.e. circuits and IC's. Secondary harware is the memory or storage area of computer.

Software is a general term used for computer Programs. A computer program is a planned, step by step set of instructions that directs the computer what to do and how to do. It turns the data into information - that makes a computer useful.

3.2 HardwareThe electrical, electronic, mechanical, and magnetic components that make up the computer system are together termed as ‘hardware.’ These include components that are responsible for user input, display, and mathematical processing. The CPU, disk drives, internal chips and wiring, modem, peripheral devices like the monitor, keyboard, mouse, printer, speakers and so forth are together termed as computer hardware. Most of the components of hardware have been described and discussed in chapter 2. But an important component to be described here is the ‘Motherboard.’

3.2.1 MotherboardA motherboard is the central Printed Circuit Board (PCB) in many modern computers and holds many crucial components of the system, while providing connectors for other peripherals. The motherboard is sometimes alternatively known as the main board or system board. It is the main component inside the case, consisting of large rectangular board with integrated circuitry that connects the rest of the parts of the computer including the CPU, the RAM, the disk drives (CD, DVD, hard disk, or any others) as well as any peripherals connected via the ports or the expansion slots.

Components directly attached to the motherboard include:The Central Processing Unit (CPU)• The chip set, mediating communication between the CPU and the other components of the system, including • main memoryRAM (Random Access Memory) • The Basic Input Output System (BIOS), including boot firmware and power management. The tasks of BIOS • are handled by operating system drivers.Internal Buses which connect the CPU to various internal components and to expansion cards for graphics and • sound. External Bus Controllers that support ports for external peripherals. These ports may be controlled directly by • the south bridge I/O controller or based on expansion cards attached to the motherboard through the PCI bus.

3.3 SoftwareComputer software, or just software, is the collection of computer programs and related data that instructs a computer to perform desired task or action. We can also say software refers to one or more computer programs and data held in the storage of the computer for some specific purposes. The term was coined to contrast to the old term hardware (meaning physical devices). In contrast to hardware, software is intangible, meaning it "cannot be touched."

There are two broad categories of software;Systems software• Application software.•

The process of software development is called programming. Knowledge of programming languages is must to develop various programs. We will first have a brief overview about programming languages and then on the types of software.


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3.4 Programming LanguagesProgramming languages are developed with the primary objective of facilitating a large number of people to use computers without the need to know in detail the internal structure of the computer. Languages are also designed to be machine independent. Ideally, one should be able to execute a program on any computer regardless of its manufacturer or model. We can choose any language for writing a program according to the need. But a computer executes programs only after they are represented internally in binary form (sequences of 1s and 0's). Programs written in any other language must be translated to the binary representation of the instructions before they can be executed by the computer.

Important categories or generations of programming languages are described below.

3.4.1 Machine Language

This is a sequence of instructions written in the form of binary numbers consisting of 1's. 0's to which the • computer responds directly. The machine language was initially referred to as code, although now the term code is used more broadly to refer to any program text.An instruction prepared in any machine language will have at least two parts. The first part is the Command or • Operation, which instructs the computer about the function to be performed. All computers have an operation code for each of its functions. The second part of the instruction is the Operand or it tells the computer where to find or store the data that has • to be manipulated. Just as hardware is classified into generations based on technology, computer languages also have a generation • classification based on the level of interaction with the machine. Machine language is considered to be the first generation language.

3.4.2 Assembly Language

When symbols (letters, digits or special characters) are used for the operation part, the address part and other • parts of the instruction code, then such representation is called as an assembly language program. This is considered to be the second generation language. Machine and assembly languages are referred to as • low level languages since the coding for a problem is at the individual instruction level.

3.4.3 High Level Language

High level languages are also called procedural languages. Programming languages such as C, COBOL, • FORTRAN and BASIC are high level languages. As the time and cost for creating machine and assembly languages are high, the high level languages were developed. A program written in a high level language should be translated into a machine compatible form and this is • done by software (language translator) called compiler. A compiler takes a high-level-language program and translates it into an executable machine-language program. There is another kind of software called interpreter which also does the translation.

3.4.4 Fourth Generation Language

Fourth Generation Language, referred to as 4GL, is a high level language that requires significantly fewer • instructions than a third generation language does to accomplish a particular task. Thus, the programmer should be able to write a program faster in 4GL than in the third generation language. Most 4GLs are non-procedural, i.e. the programmer does not have to give the details of procedure in a program, • but instead specify what is desired.

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3.4.5 Natural Language

Programming languages that use human language to give people more natural interaction with computers are • natural languages. Natural languages allow questions or commands to be framed in a more conversational way. Natural languages are the part of the field of study known as Artificial Intelligence. • Artificial intelligence is a group of related technologies that attempt to develop machines capable of emulating human-like qualities such as learning, reasoning, communicating, seeing, and hearing.

Using any of the suitable programming language, one can write a software program. As described earlier, there are two types of software, which are discussed underneath;

3.5 Systems SoftwareSystem software is computer software designed to operate the computer hardware and to provide and maintain a platform for running application software.

The most basic types of system software are:The computer BIOS and device firmware, which provide basic functionality to operate and control the hardware • connected to or built into the computer.The operating system (prominent examples being Microsoft Windows, Mac OS X and Linux), which allows • the parts of a computer to work together by performing tasks like transferring data between memory and disks or rendering output onto a display device. It also provides a platform to run high-level system software and application software.Utility software, which helps to analyze, configure, optimise and maintain the computer.•

3.5.1 BIOS

The • BIOS (Basic Input Output System) is the most fundamental software of a computer system. It is the firmware that ‘boots’ your computer, i.e. it starts computer when it is switched on. (This feature is the basis of the BIOS being called a ‘bootstrap program,’ particularly in older computer terminology.) It checks your system hardware, loads the operating system and files system from secondary storage into RAM, • executes the operating system and then turns control of the system over to the operating system.The BIOS also assists the operating system by governing the flow of data to and from peripheral devices, thus • acting as an interface between input/output devices and the operating system.The BIOS typically is provided on • EEPROM (Electrically Erasable Programmable Read Only Memory). This makes it possible to upgrade system BIOS by ‘flashing your BIOS’, i.e. writing a new program to the firmware.

3.5.2 Operating System (OS)An operating system is an essential component of a computer system and its primary objective is to make computer system convenient to use and utilise computer hardware in an efficient manner. An OS is a large collection of software, which manages resources of the computer system, such as memory, processor, file system and input/output devices. It keeps track of the status of each resource and decides who will have a control over computer resources, for how long and when.

Functions of operating systemAllocating system resources: The operating system directs the traffic inside the computer, deciding what resources • will be used and for how long.Time: Time in the CPU is divided into time slices which are measured in milliseconds. Each task that CPU does • is assigned a certain number of time slices. When time expires, another task gets a turn and the first task must wait until it has another turn. Since time slices are so small, you usually can't tell that any sharing is going on. Tasks can be assigned priorities so that high priority (foreground) tasks get more time slices than low priority (background) tasks.


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Memory: Memory must be managed also by the operating system. All those rotating turns of CPU use leave • data waiting around in buffers. Care must be taken not to lose data. One way to help out the traffic jam is to use virtual memory. This includes disk space as part of main memory. While it is slower to put data on a hard disk, it increases the amount of data that can be held in memory at one time. When the memory chips get full, some of the data is paged out to the hard disk. This is called swapping. Windows uses a swap file for this purpose.Input and output: Flow control is also part of the operating system's responsibilities. The operating system • must manage all requests to read data from disks or tape and all writes to these and to printers. To speed up the output to printers, most operating systems now allow for print spooling, where the data to be printed is first put in a file. This frees up the processor for other work in between the times when data is going to the printer. A printer can handle limited at a time. Without print spooling, one has to wait for a print job to finish before doing anything else. With it, one can request several print jobs and go on working. The print spool will hold all the orders and process them in turn.Monitoring system activities: Following are the activities monitored by the OS:•

System performance :A user or administrator can check to see whether the computer or network is getting �overloaded. Changes could be made to the way tasks are allocated. System performance would include response time and CPU utilisation.System security: Some system security is part of the operating system, though additional software can add �more security functions. For multiple users who are not all allowed access to everything, there must be a logon or login procedure where the user supplies a user name or ID and a password. An administrator must set up the permissions list of who can have access to what programs and data.

File and disk management: Keeping track of what files are where is a major job. An operating system comes • with basic file management commands, where, a user needs to be able to create directories for storing files. A user needs to copy, move, delete, and rename files. This is the category of operating system functions that the user actually sees the most. A more technical task is that of disk management. Under some operating systems, hard disk can be divided up or partitioned into several virtual disks. The operating system treats each virtual disk as a physically separate disk. Managing several physical and/or virtual disks can get pretty complex, especially if some of the disks are set up with different operating systems.

Types of operating system Batch operating system: It requires grouping of similar jobs consisting programs, data and system commands. • The suitability of this type of processing is in programs with large computation time with no need of user interaction or involvement. Some examples of such programs include payroll, forecasting, statistical analysis, and large scientific number crunching programs. Users are not required to wait while the job is being processed. They can submit their programs to system and collect the results later.Multiprogramming operating system: Multiprogramming operating systems, compared to batch operating • systems, are fairly sophisticated. They have a significant potential for improving system throughput and resource utilisation with very minor differences. Different forms of multiprogramming operating system are multitasking, multiprocessor and multi-user operating systems.Network operating system: A network operating system is a collection of software and associated protocols that • allow a set of autonomous computers, which are interconnected by a computer network, to be used together in a convenient and cost-effective manner. In a network operating system, the users are aware of existence of multiple computers and can log into remote machines and copy files from one machine to the other.Distributed operating system: A distributed operating system is one that looks like an ordinary centralised • operating system but runs on multiple independent CPUs. The key concept here is transparency. In other words, the use of multiple processors should be invisible to the user. Another way of expressing the same idea is to say that user views the system as virtual uni processor but not as a collection of distinct machines. In a true distributed system, users are not aware of where their programs are being run or where their files are residing; they are all handled automatically and efficiently by the operating system.

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3.5.3 Utility SoftwareUtility software is a kind of system software designed to help analyse, configure, optimise and maintain the computer. A single piece of utility software is usually called a utility. Utility software usually focuses on how the computer infrastructure, including the computer hardware, operating system, and application software and data storage operates. Due to this focus, utilities are often rather technical and targeted at people with an advanced level of computer knowledge.

3.6 Application SoftwareApplication software is written to enable the computer to solve a specific data processing task. A number of powerful application software packages, which does not require significant programming knowledge, have been developed. These are easy to use and learn, as compared to the programming languages. Although such packages can perform many general and special functions, there are applications where these are not found to be adequate. In such cases, application program is written to meet the exact requirements. A user application program may be written using one of these packages or a programming language.

The most important categories of software packages available are: Data Base Management Software • Spreadsheet Software • Word Processing, Desktop Publishing (DTP), Presentation Software and Graphics Software •

Data Communication Software �Statistical and Operational Research Software. �

We will have a brief overview of some of the application soft wares.

Word ProcessingWord processing is the most used computer application, which has largely replaced the typewriter. It facilitates • revision and correction of documents before they are printed. An existing document can be used as a template, or pattern, for a new one. So the user doesn't have to recreate • standard documents from scratch each time. This is a major time-saver and helps keep things consistent. Microsoft Word, WordPerfect, Lotus WordPro, and Open Office Writer are some examples of word processing • programs.

Purpose - to produce documents �Main advantage �

easy to edit documents -can reuse existing documents as a template. -

Spread sheetsA spreadsheet is the application of choice for most documents that organise numbers like budgets, financial • statements, grade sheets, and sales records. A spreadsheet can perform simple or complex calculations on the numbers entered in rows and columns. Examples • of spreadsheet programs are MS Excel, Lotus 1-2-3, Quattro Pro, and Open Office Calc.

Purpose - organising numbers �Main advantage �

can calculate using formulas -auto-update of related numbers when data changes -can display data in graphs and charts. -


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Database Management SoftwareA database is a collection of data that is to be managed, rearranged, and to be added to later. With a database • one can sort the data by name or city or postal code or by any individual item of information recorded. One can create forms to enter or update or just display the data or create reports that show just the data of interest, • like members who owe dues and so on.Both spreadsheets and databases can be used to handle much the same information, but each is optimised to handle • a different type most efficiently. The larger the number of records, the more important the differences are.Examples of databases are MS Access, dBase, FoxPro, Paradox, Approach, Oracle, Open Office Base.•

Purpose - managing data �Major Advantages �

can change the way data is sorted and displayed. -

Graphics SoftwareGraphics programs deal with pictures, static or moving, flat or 3D. There are an amazing number of different • formats for images in the world and no one program can handle them all.Adobe Photoshop is the most widely used graphics program for professionals. Paint Shop Pro is popular because • it offers most of Photoshop's features at a lower cost and with a friendlier interface. There are many other programs, of which, some specialise in handling photographs or animations or creating logos.

Purpose - to create and edit images �Major Advantages �

important tool for professionals in photo or image processing -easily creates illustrations, logos. -

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SummaryA computer system is a combination of hardware and software.• Computer hardware is the physical part of a computer.• These include components that are responsible for user input, display, and mathematical processing. The CPU, • motherboard, disk drives, internal chips and wiring, modem, peripheral devices like the monitor, keyboard, mouse, printer, speakers and so on are together termed as computer hardware.Computer software is the intangible part unlike the hardware.• Soft wares are classified as systems and application software.• Both the systems software and the application software are responsible for roles as their names suggests. Systems • software operates the hardware and maintains a platform for running application soft wares.As people need language to write, computer also requires languages to write software programs (both system • software programs and application software programs.) They are known as programming languages.Programming languages are categorised as machine language, assembly language, high level language, and • natural language. Appropriate language is chosen to write programs for systems or application software.

ReferencesBose, K. S., 1996. Hardware And Software Of Personal Computers, New Age International.• Gookin, G., 2011. PCs For Dummies, John Wiley & Sons.• Introduction To Computers: Hardware and Software [Pdf] Available at: <http://pages.cpsc.ucalgary.• ca/~tamj/2005/231W/notes/acrobat/computers_economy.pdf> [Accessed 28 May 2013].BASIC CONCEPTS IN COMPUTER HARDWARE AND BASIC CONCEPTS IN COMPUTER HARDWARE • AND SOFTWARE [Pdf] Available at: <http://wikieducator.org/images/1/11/Basic_Concepts_in_Computer_Hardware_and_Software.pdf> [Accessed 28 May 2013].Intro to Computer Hardware Chapter 1.wmv [Video online] Available at: <http://www.youtube.com/• watch?v=ZOKsmiLcSlo> [Accessed 28 May 2013].Lecture - 3 Introduction To System : Hardware [Video online] Available at: <http://www.youtube.com/• watch?v=FOyuMclwymw> [Accessed 28 May 2013]

Recommended ReadingSchneidewind, F. N., 2012. • Computer, Network, Software, and Hardware Engineering with Applications, John Wiley & Sons.Sichel, E. D., 1997. • The computer revolution: an economic perspective, Brookings Institution Press.Preez, D. A., Dyk, V. V. & Cook, A., 2008. • FCS Computer Hardware & Software L3, Pearson South Africa


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Self AssessmentThe electrical, electronic, mechanical and ____________components that make up the computer system are 1. together termed as ‘hardware’.

maintenancea. magneticb. automaticc. logicald.

Which component of the motherboard mediates communication between the CPU and the other components 2. of the system, including main memory?

Chip seta. RAMb. Biosc. Bus controllerd.

Functions of an operating system are; state which one of the following is false?3. Allocating resourcesa. Monitoring system activitiesb. Creating resourcesc. File and disk managementd.

Multitasking, multiprocessor and multi-user operating systems are sub types of which operating system?4. Network operating systema. Distributed systemb. Batch operating systemc. Multi programming operation systemd.

Data is paged out to the hard disk in case memory chips get full, this is known as ____________ 5. mappinga. swappingb. flaggingc. flappingd.

Operation and operand are parts of which category of programming language?6. Machine languagea. COBOLb. Assembly languagec. Natural languaged.

Identify the system software designed to help analyze, configure, optimise and maintain the computer;7. Windowsa. DOSb. Operating systemc. Utility softwared.

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Time in the CPU is divided into ____________.8. slicesa. sectionsb. factorsc. quartersd.

Which of the following is a non-procedural language?9. Natural languagea. Fourth generation languageb. FORTRANc. C+d.

____________are easy to learn and use as compared to the programming languages.10. System soft waresa. Machine languageb. Application soft waresc. Operation soft waresd.


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Chapter IV

Communication and Networks

Aim


explain the communications and network between computers•

elucidate types of communication channel•

explicate the standard networking protocols•

Objectives


explain the role of communication channels in networks•

elucidate client-to-peer and peer-to-peer network configuration•

enlist the types of topology for networks•

Learning outcome


identify and list network communication channels•

understand wired and wireless communication channels•

describe types of topologies and types of networks•

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4.1 IntroductionA standalone computer in today’s context is not very useful, but coupled with communication technology; it opens up an enormous repository of information to its users. The concept of data communication evolved from sharing the computation power of a computer along with various resources available in a computer environment such as printers, hard disk and so on.

With increasing demand for exchange of information across the globe, the need for data communication has increased in many folds. Due to physical constraints involved in connecting two remote points, physical data communication has emerged as an instant solution.

4.2 Computer NetworksIn human life, people connect and relate to each other for various reasons like friendship, common goals, and common work area. Whatever the reason may be, these connections form networks of people. Similarly, for computers, although a standalone computer is of great help and assistance, when more than one computer is involved as a part of network, their beneficial value increases enormously. Computers may be networked (physically), through wires or connected without wires. We will have a detailed account of definitions, and concepts related to communication and computer networks in this chapter.

Computer networks may be defined as, “a collection of computers and devices interconnected by communication channels that facilitate communication among users and allows users to share resources.”

4.3 Goals of NetworksNetworks are set up to satisfy certain basic goals. Some of the goals that a network should achieve are:

Cost reduction by sharing hardware and software resources• Provide high reliability by having multiple sources of supply• Provide an efficient means of transport for large volumes of data among various locations• Provide inter-process communication among users and processors• Reduction in delay driving data transport• Increase productivity by making it easier to share data amongst users• Repairs, upgrades, expansions, and changes to the network should be performed with minimal impact on the • majority of network usersStandards and protocols should be supported to allow many types of equipment from different vendors to share • the network (inter operability)Provide centralised/distributed management and allocation of network resources like host processors, transmission • facilities and so forth.

4.4 Communication ChannelsTo network computers, a physical or non-physical connection needs to be established. This can be achieved using communication channels.

A communication channel is the path—transmission medium—over which information travels in a communication • system from its source to its destination. Channels are also called links, lines, or media.Communication devices use analog electromagnetic signals representing data to transmit information from • one device to another. Electromagnetic signals can travel through vacuum, air or other transmission media like wire, fibre optics and so on.Communication channels which use a physical medium for transmission (twisted pair wire, coaxial cable, and • fibre optic cable) are called wired channels. Communication channels which do not require any physical medium for transmission (radio, microwave and communication satellite) are called wireless channels. The basis for all communication channels both wired and wireless, are the electromagnetic spectrum. The • spectrum covers frequencies for voice, radio waves, infrared light, visible light, and ultraviolet light and X, gamma and cosmic rays.


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4.4.1 Wired Channels (Twisted-pair Wire, Coaxial Cable and Fibre-optic Cable)These media are also called guided media since they provide a conduit from one device to another, a signal travelling along any of these media is directed and contained by the physical limits of the medium.

Wired communication channels use the following physical media:Twisted-pair wire• Coaxial cable• Fibre-optic cable•

Optical fibre is a glass or plastic cable that accepts and transports signals in the form of light. Let us look more closely at each of the medium.

Twisted-pair WireTwisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form • of electrical current. Twisted-pair wire are of two types: Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP).

Unshielded Twisted Pair (UTP) is the most common type and also used in telephone lines. A twisted pair �consists of two conductors (copper) each with its own coloured plastic insulation and twisted around each other. Twisted pair configuration reduces interference from electrical field as compared to parallel pair configuration. Unshielded twisted pair is currently the cable standard for most networks. It is relatively inexpensive, easy to install, very reliable, and easy to maintain and expand. UTP support a maximum data rate of 155 Mbps.Shielded Twisted Pair (STP) wire has a metal foil or braided mesh covering that encases each pair of �insulated conductors. The metal casing prevents the penetration of electromagnetic noise and the quality of transmission improves. In all other respects it resembles UTP.

Coaxial CableCoaxial cable (simply called coax) has a central core conductor of solid or standard wire (usually copper) enclosed • in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid or a combination of the two (also usually copper).The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes • the circuit. This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover. • Coaxial cable carries signals of higher frequency ranges than twisted-pair wire. Often many coaxial cables are bundled together.As a result of extra insulation, coaxial cable is much better than twisted pair wiring at resisting noise. Also, it • is faster than UTP (supports a maximum data rate of 200 Mbps).

Fibre-optic CableThe cable consists of a core made of fine glass or plastic fibre. The core is surrounded by a refractive layer • called the cladding that effectively traps the light and keeps it bouncing along the central fibre. In most cases, the cladding is covered by a buffer layer that protects it from moisture. The entire cable is encased in an outer jacket. Both core and cladding can be made of glass or plastic but must • be of different densities. In addition, the core must be ultra pure and completely regular to ensure distortion- free signals. Since light has higher frequency on the electromagnetic spectrum than other types of radiation such as radio waves, • a single fibre-optic channel can carry more information than most other means of information transmission. Hundreds of strands of optical fibres (each as thin as human hair) can be housed in a single fibre-optic cable. They • represent the most promising type of transmission medium and their usage is fast increasing with the time.

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The major advantages of fibre-optic cable are:Noise resistance: since fibre-optic transmission uses light rather than electricity, noise (electromagnetic • interference) is not a factor. Less signal attenuation: s signal can run for miles without requiring regeneration.• Higher bandwidth: a fibre-optic cable can support much higher bandwidth than both twisted-pair and coaxial • cable. It can support data rates of the order of gigabits per second (Gbps). The data rates are limited not by the medium but by the signal generation and reception technology available.•

The main disadvantages of fibre-optic cable are: high cost• difficulties in their installation/maintenance• fragility.•

4.4.2 Wireless Channels (Radio Link, Microwave Link, Satellite Communication)

Wireless channels transport electromagnetic waves from one point to another through the atmosphere or space • without using a physical conductor. The section of electromagnetic spectrum designated for wireless channels called radio spectrum ranges from • 3GHz to 300 GHz and is divided into eight bands each regulated by government authorities. These bands are rated from very low frequency (VLF) to extremely high frequency (EHF). Radio link, microwave • link and satellite communication utilise frequencies in the radio spectrum for data communication.

Radio LinkRadio link, also called as broadcast radio, deals with transmission of data over long distance. A transmitter is • required to send messages and a receiver to receive them. Depending upon the type of the service, it uses a range of frequencies (3 kHz to 30MHz). In the lower frequencies • of radio spectrum, several broadcast radio bands are reserved for conventional AM/FM radio, broadcast television and private radio services.Radio link can support a bandwidth up to 2 Mbps. It is easy to install and involves low recurring costs.•

Microwave LinkMicrowave link, also called as microwave radio, utilises point to point radio transmissions at the super-high • frequency (SHF) and extremely high frequency (EHF) bands. Microwaves do not follow the curvature of the earth and therefore require line-of-sight transmission and reception equipment. Microwave dishes, which contain transceivers (sending and receiving devices) and antennas are set up on towers • or buildings to establish the link. Microwave stations need to be placed at some distances (a few kilometres) from each other with no obstruction • in between. The size of the dish varies with the distance. A string of microwave relay stations is used with each station receiving incoming messages, boosting the signal • strength, and relaying the signal to the next station.Microwave link supports a bandwidth up to 45Mbps and is widely used in data communication.•

Satellite Communication To overcome line-of-sight constraint of microwave earth stations, communication satellites (microwave ‘sky • stations’) are used. Communication satellites are microwave relay stations in orbit around the earth. Transmitting a signal from a ground station to a satellite is called up linking; the reverse is called down • linking.


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Geosynchronous satellites are most commonly used in data communication. A geosynchronous satellite is placed • in geostationary earth orbit (nearly 36,000 km directly above the equator) where it travels at the same speed as the earth and appears to an observer on the ground to be stationary. Consequently, microwave earth stations are always able to beam signals to a fixed location above. The orbiting • satellite has solar powered transceivers to receive the signals, amplify them and re-transmit them to another earth station.Satellite communication provides transmission capabilities to and from any location on earth, no matter how • remote. This advantage makes high quality communication available to less developed regions without requiring huge • investment in ground-based infrastructure. Satellite communication supports high bandwidths capable of carrying large amounts of data and ensures low • error rates.

4.5 Transmission TechnologyAfter connecting computers using some communication channel described above, data needs to be transmitted from one computer to another. Transmission technology is necessarily used to do so. There are two types of transmission technologies:

Broadcast networks• Point-to-point or Switched networks•

4.5.1 Broadcast Networks Broadcast networks have a single communication channel that is shared by all the machines on the network. In this type of network, short messages sent by any machine are received by all the machines on the network. The packet contains an address field, which specifies for whom the packet is intended. All the machines, upon receiving a packet check for the address field, if the packet is intended for itself, it processes it and if not the packet is just ignored.

This mode of operation is known as Broadcasting. Some broadcast networks also support transmission to a subset of machines and this is known as Multicasting. One possible way to achieve multicasting is to reserve one bit to indicate multicasting and the remaining (n-1) address bits contain group number. Each machine can subscribe to any or all of the groups. Broadcast networks are easily configured for geographically localised networks. Broadcast networks may be static or dynamic, depending on how the channel is allocated.

The different types of broadcast networks are: Packet Radio Networks• Satellite Networks• Local Area Networks. •

Packet Radio broadcasting differs from satellite network broadcasting in several ways. In particular, stations have limited range introducing the need for radio repeaters, which in turn affects the routing, and acknowledges schemes. Also the propagation delay is much less than for satellite broadcasting.

LAN (Local Area Network) is a computer network that spans over a relatively small area. Most LANs are confined to a single building or group of buildings within a campus. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN). There are many different types of LANs, Ethernets being the most common for PCs. A more detailed description of LAN will be covered later in the chapter.

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4.5.2 Point-to-Point or Switched Networks

Point–to-point or switched, networks are those in which there are many connections between individual pairs • of machines. In these networks, when a packet travels from source to destination it may have to first visit one or more intermediate machines.Routing algorithms play an important role in point-to-point or switched networks, because often multiple routes of • different lengths are available. An example of switched network is the international dial-up telephone system. In Switched network, the temporary connection is established from one point to another for either the duration • of the session (circuit switching) or for the transmission of one or more packets of data (packet switching).

Two types of point- to-point or switched networks are: Circuit Switched Networks

Circuit Switched networks use a networking technology that provides a temporary, but dedicated connection • between two stations no matter how many switching devices are used in the data transfer route. This was originally developed for the analog based telephone system in order to guarantee steady and consistent • service for two people engaged in a phone conversation. Analog circuit switching has given way to digital circuit switching, and the digital counterpart still maintains • the connection until broken (one side hangs up.) This means, bandwidth is continuously reserved and “silence is transmitted” just the same as digital audio in voice conversation.

Packet Switched Networks Packet Switched Networks use a networking technology that breaks up a message into smaller packets for • transmission and switches them to their destination. Unlike circuit switching, which requires a constant point-to-point circuit to be established, each packet in a packet- • switched network contains a destination address. Thus, all packets in a single message do not have to travel the same path. They can be dynamically routed over the network as lines become available or unavailable. The destination computer reassembles the packets back into their proper sequence. Packet switching efficiently • handles messages of different lengths and priorities. Higher-level protocols, such as TCP/IP, IPX/SPX and NetBIOS, are also packet based and are designed to ride • over packet-switched topologies. Public packet switching networks may provide value added services, such as protocol conversion and electronic mail.

To understand the transmission technology better, we also need to understand the concept of ‘bandwidth’ and its significance in data transmission.

4.5.3 Bandwidth

The bandwidth of a communication channel determines its information-carrying capacity. Bandwidth implies • how much data in form of text, voice, video and so on, can be sent through a communication channel in a given amount of time. For analog signals, bandwidth is expressed in hertz (Hz) and specifies the range of frequencies that the channel • is capable of transmitting without interference or signal loss.Here bandwidth indicates the difference between the lowest and highest frequencies transmitted. • For example, a microwave link within the range of 800-900 megahertz has a bandwidth of 100 megahertz. • The wider the bandwidth, the faster is the data transmission. The narrower the bandwidth the greater the loss of transmission power, which is overcome by using relays or repeaters that rebroadcast the original signals. Broadband connections are characterised by very high speed. For digital signals, bandwidth is measured in bits per second (bps). The type of the communication channel • determines the channel’s bandwidth.


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For example, fibre-optic cable used for high speed internet access has more bandwidth than conventional copper-wire telephone lines. High quality voice, music and video transmissions require high bandwidth of the communication channel. Bandwidth plays a critical role while designing a network.

4.6 Network ConfigurationConfiguration refers to the design of computers within a network to obtain maximum efficiency. There are two types of network configuration:

4.6.1 Client-Server Network

Client-Server architecture is one in which the client (personal computer or workstation) is the requesting machine • and the server is the supplying machine, both of which are connected via a local area network (LAN) or wide area network (WAN).A client/server network is called Centralised or Server based network. The client contains the user interface and • may perform some or all of the application processing. Servers can be high-speed microcomputers, minicomputers or even mainframes. A database server maintains the databases and processes requests from the client to extract data from or update • the database. An application server provides additional business processing for the clients. The term client/server is sometimes used to contrast a peer-to-peer network, in which any client can also act as • a server. In that case, a client/server entails having a dedicated server. However, client/server architecture means more than dedicated servers. Simply downloading files from or • sharing programs and databases on a server is not true client/server either. True client/server implies that the application was originally designed to run on a network and that the network infrastructure provides the same quality of service as traditional mini and mainframe information systems.

4.6.2 Peer-to-peer Network

A type of network in which each workstation has equal capabilities and responsibilities is called peer-to-peer • network. Each workstation acts as both a client and a server. There is no central repository for information and there is no central server to maintain. • Data and resources are distributed throughout the network, and each user is responsible for sharing data and • resources connected to their system. This differs from client/server architectures, in which some computers are dedicated to serving the others. Peer-to-peer networks are generally simpler and less expensive, but they usually do not offer the same performance • under heavy loads. A peer-to-peer network is also known as a distributed network.

4.7 Network ModelsIn order to divide the workload and to simplify the system design, most of the networks today are organised as a series of stacked layers with each layer stacked over another system design. It is furthermore simplified because with a layered architecture, the design has to only concern about the layer in question and not worry about the architecture in a macro sense.

Network protocols are standards that allow computers to communicate. A protocol defines how computers identify one another on a network, the form that the data should take in transit, and how this information is processed once it reaches its final destination. Protocols also define procedures for handling lost or damaged transmissions or "packets.”

4.7.1 OSI Reference Model

The Open System Interconnection (OSI) model is a set of protocols that attempt to define and standardise the • data communications process; we can say that it is a concept that describes how data communications should take place.

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The OSI model was set by the International Standards Organisation (ISO) in 1984, and it is now considered the • primary architectural model for inter-computer communications. The Open Systems Interconnection (OSI) reference model describes how information from a software application • in one computer moves through a network medium to a software application in another computer. The OSI reference model is a conceptual model composed of seven layers specifying particular network functions • and into these layers are fitted the protocol standards developed by the ISO and other standard bodies. The OSI model divides the tasks involved with moving information between networked computers into seven • smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers.Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. • This enables the solutions offered by one layer to be updated without affecting the other layers.

Application LayerFacilitates communication betweensoftware application like outlook, IE

Presentation LayerData Representation and Encryption

Session LayerInterhost Communication

Transport LayerEnd-to-End connection and reliability

Network Layerpath determination and logical

addressing

Data Link LayerMAC and LLC - Physical Addressing

Physical LayerMedia, signal and binary

transmmission

DATA

OSI MODEL

SEGMENTS

PACKETS

FRAMES

BITS

LAYERS

Fig. 4.1 OSI reference model(Source: http://www.networkguruz.com/wp-content/uploads/2008/06/osi-reference-model.jpg)

As seen in the figure, there are 7 layers of the OSI model. These are as follows:Application Layer (Layer 7)

The application layer is probably the most easily misunderstood layer of the model. This top layer defines the • language and syntax that programs use to communicate with other programs. The application layer represents the purpose of communicating in the first place. • For example, a program in a client workstation uses commands to request data from a program in the server. • Common functions at this layer are opening, closing, reading and writing files, transferring files and e-mail messages, executing remote jobs and obtaining directory information about network resources and so on.

Presentation Layer (Layer 6) The presentation layer performs code conversion and data reformatting (syntax translation). As a translator of • the network; it makes sure that the data is in the correct form for the receiving application. When data are transmitted between different types of computer systems, the presentation layer negotiates and • manages the way data is represented and encoded.


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For example, it provides a common denominator between ASCII and EBCDIC machines as well as between • different floating point and binary formats. Sun’s XDR and OSI’s ASN.1 are two protocols used for this purpose. This layer is also used for encryption and decryption and it also provides security features through encryption • and decryption.

Session Layer (Layer 5) The session layer decides when to turn communication on and off between two computers. It provides the • mechanism that controls the data-exchange process and coordinates the interaction (communication) between them in an orderly manner. It sets up and clears communication channels between two communicating components. It determines one-way • or two-way communications and manages the dialogue between both parties.For example, it makes sure that the previous request has been fulfilled before the next one is sent. It also marks • significant parts of the transmitted data with checkpoints to allow fast recovery in the event of a connection failure.

Transport layer (Layer 4) The transport layer is responsible for overall end-to-end validity and integrity of the transmission, i.e. it ensures • that data is successfully sent and received between two computers. The lower data link layer (layer 2) is only responsible for delivering packets from one node to another. Thus, if • a packet gets lost in a router somewhere in the enterprise internet, the transport layer will detect that. It ensures that if a 12MB file is sent, the full 12MB is received. If data is sent incorrectly, this layer has the responsibility of asking for retransmission of the data. Specifically, • it provides a network-independent, reliable message-independent, reliable message-interchange service to the top three application-oriented layers. This layer acts as an interface between the bottom and top three layers. By providing the session layer (layer • 5) with a reliable message transfer service, it hides the detailed operation of the underlying network from the session layer.

Network layer (Layer 3) The network layer establishes the route between the sending and receiving stations. The unit of data at the • network layer is called a packet. It provides network routing and flow and congestion functions across computer-network interface. It makes a decision as to where to route the packet based on information and calculations from other routers, • or according to static entries in the routing table. It examines network addresses in the data instead of physical addresses seen in the Data Link layer. • The network layer establishes, maintains, and terminates logical and/or physical connections. It is responsible • for translating logical addresses, or names, into physical addresses. The main device found at the network layer is a router.

Data Link Layer (Layer 2) The data link layer groups the bits that we see on the Physical layer into Frames. It is primarily responsible for • error-free delivery of data on a hop. The data link layer is split into two sub-layers i.e.,

The Logical Link Control (LLC) �Media Access Control (MAC). �

The data link layer handles the physical transfer, framing (the assembly of data into a single unit or block), • flow control and error-control functions (and retransmission in the event of an error) over a single transmission link; it is responsible for getting the data packaged and onto the network cable. The data link layer provides the network layer (layer 3) reliable information-transfer capabilities.

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The main network device found at the data link layer is a bridge. This device works at a higher layer than the • repeater and therefore is a more complex device. It has some understanding of the data it receives and can make a decision based on the frames it receives as to • whether it needs to let the information pass, or can remove the information from the network. This means that the amount of traffic on the medium can be reduced and therefore, the usable bandwidth can be increased.

Physical Layer (Layer 1) The data units on this layer are called bits. This layer defines the mechanical and electrical definition of the • network medium (cable) and network hardware. This includes how data is impressed onto the cable and retrieved from it. The physical layer is responsible for passing bits onto and receiving them from the connecting medium. This layer • gives the data-link layer (layer 2) its ability to transport a stream of serial data bits between two communicating systems; it conveys the bits that move along the cable. It is responsible for ensuring that the raw bits get from one place to another, no matter what shape they are in, • and deals with the mechanical and electrical characteristics of the cable.

4.7.2 TCP/IP Protocol

TCP/IP stands for Transmission Control Protocol/Internet Protocol. • It is a protocol suite used by most communications software. TCP/IP is a robust and proven technology that was • first tested in the early 1980s on ARPA Net, the U.S. military’s Advanced Research Projects Agency Network, and the world’s first packet-switched network. TCP/IP was designed as an open protocol that would enable all types of computers to transmit data to each other • via a common communications language. TCP/IP is a layered protocol similar to the ones used in all the other major networking architectures, including • IBM’s SNA, Windows' NetBIOS, Apple’s AppleTalk, Novell’s NetWare and Digital's DECnet. There are 4 layers. Layering means that after an application initiates the communications, the message (data) to • be transmitted is passed through a number of stages or layers until it actually moves out onto the wire. The data are packaged with a different header at each layer. At the receiving end, the corresponding programs • at each protocol layer unpack the data, moving it “back up the stack” to the receiving application. TCP/IP is composed of two major parts: TCP (Transmission Control Protocol) at the transport layer and IP • (Internet Protocol) at the network layer. TCP is a connection-oriented protocol that passes its data to IP, which is connectionless one. TCP sets up a • connection at both ends and guarantees reliable delivery of the full message sent. TCP tests for errors and requests retransmission if necessary, because IP does not do that.

4.8 Network TopologiesTopology refers to the shape of a network, or the network’s layout. How different nodes in a network are connected to each other and how they communicate with each other is determined by the network's topology. Topologies are either physical or logical.

Some of the most common network topologies are:Bus topology• Star topology• Ring topology• Tree topology• Mesh topology•


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The parameters that are to be considered while selecting a physical topology are:Ease of installation• Ease of reconfiguration• Ease of troubleshooting.•

Bus TopologyIn Bus topology, all devices are connected to a central cable, called the bus or backbone. The bus topology • connects workstations using a single cable. Each workstation is connected to the next workstation in a point-to-point fashion. All workstations connect to • the same cable.

BackboneCable tap

Drop cable

Terminator

Fig. 4.2 Bus topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Bus Topology Installation is easy and cheap when compared to other topologies• Connections are simple and this topology is easy to use• Requires less cabling. •

Disadvantages of Bus Topology Used only in comparatively small networks• As all computers share the same bus, the performance of the network deteriorates when the number of computers • is increased beyond a certain limitFault identification is difficult• A single fault in the cable stops all transmission. •

Star TopologyStar topology uses a central hub through which all components are connected. In a Star topology, the central • hub is the host computer, and there is a terminal at the end of each connection.Nodes communicate across the network by passing data through the hub. A star network uses a significant amount • of cable as each terminal is wired back to the central hub, even if two terminals are side by side but several hundred meters away from the host. The central hub makes all routing decisions, and all other workstations can be simple.

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Fig. 4.3 Star topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Star Topology Easy to install and wire• No disruptions to the network when connecting or removing devices• Easy to detect faults and to remove parts. •

Disadvantages of Star Topology Requires more cable length than a linear topology• If the hub, switch, or concentrator fails, nodes attached are disabled• More expensive than linear bus topologies because of the cost of the hubs, etc.•

Ring TopologyIn ring topology, all devices are connected to one another in the shape of a closed loop, so that each device is • connected directly to two other devices, one on either side of it.Each terminal is connected to two other terminals (the next and the previous), with the last terminal being • connected to the first. Data is transmitted around the ring in one direction only; each station passing on the data to the next station till it reaches its destination. Information travels around the ring from one workstation to the next. Each packet of data sent on the ring is • prefixed by the address of the station to which it is being sent. When a packet of data arrives, the workstation checks to see if the packet address is the same as its own, if it is, it grabs the data in the packet. If the packet does not belong to it, it sends the packet to the next workstation in the ring. The common implementation of this topology is token ring. A break in the ring causes the entire network to • fail. Individual workstations can be isolated from the ring.

Fig. 4.4 Ring topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)


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Advantages of Ring Topology Easy to install and modify the network• Fault isolation is simplified• Unlike bus topology, there is no signal loss in ring topology because the tokens are data packets that are re-• generated at each node.

Disadvantages of Ring Topology Adding or removing computers disrupts the entire network • A break in the ring can stop the transmission in the entire network• Finding fault is difficult• Expensive when compared to other topologies. •

Tree TopologyTree topology is a LAN topology in which only one route exists between any two nodes on the network. The • pattern of connection resembles a tree in which all branches spring from one root. Tree topology is a hybrid topology. It is similar to the star topology but the nodes are connected to the secondary • hub, which in turn is connected to the central hub. In this topology, groups of star-configured networks are connected to a linear bus backbone.

Fig. 4.5 Tree topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Tree TopologyInstallation and configuration of network is easy• Less expensive when compared to mesh topology• Faults in the network can be detected• The addition of the secondary hub allows more devices to be attached to the central hub• Supports multiple cable types like shielded twisted pair cable, unshielded twisted pair cable, ordinary telephone • cable and so forth.

Disadvantages of Tree TopologyFailure in the central hub brings the entire network to a halt• More cabling is required when compared to bus topology because each node is connected to the central hub.•

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Mesh TopologyMesh topologies are used in critical connection of host computers (typically telephone exchanges). Alternate • paths allow each computer to balance the load to other computer systems in the network by using more than one of the connection paths available. A fully connected mesh network therefore has n (n-1)/2 physical channels to link n devices. To accommodate • these, every device on the network must have (n-1) input/output ports.

Fig. 4.6 Mesh topology(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Advantages of Mesh Topology Use of dedicated links eliminates traffic problems • Failure in one of the computers does not affect the entire network• Point-to-point link makes fault isolation easy• It is robust• Privacy between computers is maintained as messages travel along dedicated path. •

Disadvantages of Mesh Topology The amount of cabling required is high• A large number of I/O (input/output) ports are required.•

4.9 Types of NetworksFor using any of the suitable communication channels, network configuration, and topology, there are different types of networks which are based on geographical areas of work. Common examples of network are Novell network, ARPANET and internet.

Features of Local Area Network (LAN) are:All connected devices in the network share the transmission media • Each device connected in the network can either operate standalone or in the network•


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Area covered is small• Data transfer rates are high, usually 1Mbps-100Mbps (Million of bits per second)• Each device connected in the network can communicate with any other device in network• Cost of setting up the network is usually low.•

Metropolitan Area Network (MAN): Metropolitan Area Network is a computer network designed for a town or city. In terms of geographic area, MAN’s are larger than LANs, but smaller than wide-area networks (WANs). MAN’s are usually characterised by very high-speed connections using fibre optical cable or other digital media.

The typical characteristics of a MAN are: Confined to a larger area than a LAN and can range from 10km to a few 100km in length• Slower than a LAN but faster than a WAN • Operates at a speed of 1.5 to 150 Mbps• Expensive equipment• Moderate error rates. •

Wide Area Network (WAN)Wide Area Network is a computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). They can connect networks across cities, states or even countries.

Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites.

The typical characteristics of a WAN are: A WAN can range from 100km to 1000km and the speed between cities can vary form1.5 Mbps to 2.4 Gbps• WAN supports large number of computers and multiple host machines• Various segments of network are interconnected using sophisticated support devices like routers and • gatewaysUsually the speed is much slower than LAN speed• Highest possible error rate compared to LAN & MAN.•

An overview and comparison of different characters of types of networks is given below.

NETWORK SIZE TRANSMISSION MEDIA MAXIMUM DISTANCE

Local Area Network Confined to building or campus

Cable is used Covers up to 10 km

Metropolitan Area Network

Network confined to city or town

Different hardware & transmission media are used

Covers the area of a city or town

Wide Area Network Larger than MAN Telephone lines, radio waves, leased lines or satellites

Covers a number of cities or countries

Table 4.1 Types of networks(Source: http://www.egyankosh.ac.in/bitstream/123456789/7399/1/Unit%201.pdf)

Thus, computers in a networked environment provide numerous advantages when compared to computers in a standalone environment. The immense benefits that the computer networks provide are in the form of excellent sharing of computational resources, computational load, and increased level of reliability, economy and efficient person-to-person communication.

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SummaryComputer network is a collection of computers and a device interconnected by communication channels that • facilitate communication among users and allows users to share resources.Communication channels which use a physical medium for transmission (twisted pair wire, coaxial cable, and • fibre optic cable) are called wired channels. Communication channels which do not require any physical medium for transmission (radio, microwave and communication satellite) are called wireless channels. The basis for all communication, a channel both wired and wireless, is the electromagnetic spectrum. The • spectrum covers frequencies for voice, radio waves, infrared light, visible light, and ultraviolet light and X, gamma and cosmic rays.Configuration refers to the design of computers within a network to obtain maximum efficiency. There are two • types of network configuration, client-to-server and peer-to-peer.There are two types of transmission technologies, broadcast networks and point-to-point or switched • networksStandards for network communication followed are OSI reference model and TCP/IP protocol• Topology refers to the shape of a network, or the network’s layout. How different nodes in a network are • connected to each other and how they communicate with each other is determined by the network's topology. Topologies are either physical or logical.Some of the most common network topologies are: bus topology, star topology, ring topology, tree topology, • and mesh topology.Types of networks are LAN, MAN, WAN. Common examples of network are Novell network, ARPANET and • internet.Benefits that the computer networks provide are in the form of excellent sharing of computational • resources, computational load, and increased level of reliability, economy and efficient person-to-person communication.

ReferencesKesidis, G., 2007. • An Introduction to Communication Network Analysis, John Wiley & Sons.Stallings, W., 2007. • Data And Computer Communications, 8/E, 8th ed. Pearson Education India.Hoang, D. B. & Pye, K. J., • Computer Communication Networks - Lecture Notes [Pdf] Available at: <ftp://cs.istu.ru/public/docs/other/_New/Sciense/books.pdox.net/Lecture@2520Notes/Computer%20Communication%20Networks%20-%20Latrobe.pdf> [Accessed 28 May 2013].Computer networks, data communication and Internet• [Pdf] Available at: <http://www.vub.ac.be/BIBLIO/nieuwenhuysen/courses/chapters/network.pdf> [Accessed 28 May 2013].Protocols and Computer Networks part 1• [Video online] Available at: <http://www.youtube.com/watch?v=Q3SsVO0eSOU> [Accessed 28 May 2013]Prof. Ghosh, S., L• ecture -1 Emergence of Networks & Reference Models [Video online] Available at: <http://www.youtube.com/watch?v=3DZLItfbqtQ&list=PLD6F332057F76C54C> [Accessed 28 May 2013]

Recommended ReadingKasera, S. & Narang, N., 2005. • Communication Networks: Principles and Practice, Tata McGraw-Hill Education.Bagad, V.S. & Dhotre, I. A., 2009. • Computer Communication Networks, Technical Publications.Mir, F. N., 2006.• Computer and Communication Networks, Pearson Education.


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Self AssessmentWhich of the following is not a goal of computer networks?1.

Cost reduction by sharing hardware and software resourcesa. Provide high reliability by having multiple sources of supplyb. Increase productivity by making data un-sharablec. Repairs, upgrades, expansions, and changes to the network should be performed with minimal impact on d. the majority of network users

Noise resistance, higher bandwidth, and less signal attenuation are advantages of using which type of connecting 2. channel?

Shielded twisted pair cablea. Fiber optic cableb. Unshielded twisted pair cablec. Coaxial cabled.

Geosynchronous satellite is placed in geostationary earth orbit where it travels at the ____________as the 3. earth.

same speeda. double speedb. half the speedc. maximum speedd.

When broadcast networks support transmission to a subset of machines, it is known as ____________.4. broadcastinga. transmissionb. networkingc. multicastingd.

Routing algorithms play an important role in which type of network transmission?5. Switched networksa. Packet radio networksb. Satellite networksc. Broadcast networksd.

OSI model is a set of protocols that attempt to define and____________-the data communications process.6. authorisea. standardiseb. speed-upc. eased.

‘Packet’ is the unit of data in which layer of the OSI model?7. Application layera. Transport layerb. Network layerc. Physical layerd.

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TCP/IP is a protocol suite used by most ____________software.8. networka. systemsb. applicationc. communicationsd.

Which are the parameters that are to be considered while selecting a physical topology? (State which is not 9. TRUE)

Ease of installationa. Ease of drawing the networkb. Ease of reconfigurationc. Ease of troubleshootingd.

Computers connected to a wide-area network are often connected through: (State which is not TRUE)10. Connectorsa. Public networks, b. Leased lines c. Satellites d.


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Chapter V

Data processing

Aim

The aim of this chapter is to:

introduce data processing•

elucidate architecture of computer system•

discuss types of data•

Objectives

The objectives of this chapter are to:

explain data capturing •

discuss organisation of relative file •

define data and information•

Learning outcome

At the end of this chapter, you will be able to:

analyse various operations performed on files •

explain CPU organisation•

understand file organisation •

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5.1 IntroductionData processing is any computer process that converts data into information. The processing is usually assumed to be automated and running on a mainframe, minicomputer, microcomputer, or personal computer. Because data are most useful when well-presented and actually informative, data processing systems are often referred to as information systems to emphasise their practicality. Nevertheless, both terms are roughly synonymous, performing similar conversions; data-processing systems typically manipulate raw data into information, and likewise information systems typically take raw data as input to produce information as output.

To better market their profession, a computer programmer or a systems analyst that might once have referred, such as during the 1970s, to the computer systems that they produce as data-processing systems more often than not nowadays refers to the computer systems that they produce by some other term that includes the word information, such as information systems, information technology systems, or management information systems.

In the context of data processing, data are defined as numbers or characters that represent measurements from the real world. A single datum is a single measurement from the real world. Measured information is then algorithmically derived and/or logically deduced and/or statistically calculated from multiple data. Information is defined as either a meaningful answer to a query or a meaningful stimulus that can cascade into further queries.

More generally, the term data processing can apply to any process that converts data from one format to another, although data conversion would be the more logical and correct term. From this perspective, data processing becomes the process of converting information into data and also the converting of data back into information. The distinction is that conversion doesn’t require a question (query) to be answered.

For example, information in the form of a string of characters forming a sentence in English is converted or encoded from a keyboard’s key-presses as represented by hardware oriented integer codes into ASCII integer codes after which it may be more easily processed by a computer not as merely raw, amorphous integer data, but as a meaningful character in a natural language’s set of graphemes and finally converted or decoded to be displayed as characters, represented by a font on the computer display. In that example we can see the stage-by-stage conversion of the presence of and then absence of electrical conductivity in the key-press and subsequent release at the keyboard from raw substantially meaningless integer hardware-oriented data to evermore-meaningful information as the processing proceeds toward the human being.

A more conventional example of the established practice of using the term data processing is that a business has collected numerous data concerning an aspect of its operations and that this multitude of data must be presented in meaningful, easy-to-access presentations for the managers who must then use that information to increase revenue or to decrease cost. That conversion and presentation of data as information is typically performed by a data processing application.

When the domain from which the data are harvested is a science or engineering, data processing and information systems are considered too broad of terms and the more specialised term data analysis is typically used, focusing on the highly-specialised and highly-accurate algorithmic derivations and statistical calculations that are less often observed in the typical general business environment. This divergence of culture is exhibited in the typical numerical representations used in data processing versus numerical; data processing’s measurements are typically represented by integers or by fixed point or binary-coded decimal representations of real numbers whereas the majority of data analysis’s measurements are often represented by floating point representation of real numbers.

Practically all naturally occurring processes can be viewed as examples of data processing systems where “real world” information in the form of pressure, light, etc. are converted by human observers into electrical signals in the nervous system as the senses we recognise as touch, sound, and vision. Even the interaction of non-living systems may be viewed in this way as rudimentary information processing systems. Conventional usage of the terms data processing and information systems restricts their use to refer to the algorithmic derivations, logical deductions, and statistical calculations that recur perennially in general business environments, rather than in the more expansive sense of all conversions of real-world measurements into real world information in, say, an organic biological system or even a scientific or engineering system.


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5.1.1 DataData are any facts, numbers, or text that can be processed by a computer. Today, organisations are accumulating vast and growing amounts of data in different formats and different databases. This includes:

operational or transactional data such as, sales, cost, inventory, payroll, and accounting• non-operational data, such as industry sales, forecast data, and macro economic data• meta data - data about the data itself, such as logical database design or data dictionary definitions•

5.1.2 InformationThe patterns, associations, or relationships among all this data can provide information. For example, analysis of retail point of sale transaction data can yield information on which products are selling and when.

5.1.3 Types of DataThink about any collected data that you have experience of; for example, weight, sex, ethnicity, job grade, and consider their different attributes. These variables can be described as categorical or quantitative. The table summarises data types and their associated measurement level, plus some examples. It is important to appreciate that appropriate methods for summary and display depend on the type of data being used. This is also true for ensuring the appropriate statistical test is employed.

Type of Data Level of Measurement Examples

Categorical

Nominal (no inherent order in categories) Eye color, ethnicity, diagnosis

Ordinal (categories have inherent order) Job grade, age groups

Binary (2 categories – special case of above) Gender

Quantitative (Interval/Ratio) (NB units of measurement used)

Discrete (usually whole numbers) Size of household (ratio)

Continuous (can, in theory, take any value in a range, although necessarily recorded to a predetermined degree of precision)

Temperature °C/°F (no absolute zero) (interval) Height, age (ratio)

Table 5.1 Types of Data

5.2 Input, Processing and outputWhenever a computer is used it must work its way through three basic stages before any task can be completed. These are input, processing and output. A Computer works through these stages by running a program. A program is a set of step-by-step instructions which tells the computer exactly what to do with the input in order to produce the required output.

5.2.1 InputThe input stage of computing is concerned with getting the data needed by the program into the computer. Input devices are used to do this. The most commonly used input devices are the mouse and the keyboard.

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5.2.2 ProcessingThe program contains instructions about what to do with the input. During the processing stage the compute follows these instructions using the data which has just been input. What the computer produces at the end of this stage, the output, will only be as good as the instructions given in the program. In other words if garbage has been put in to the program, garbage is what will come out of the computer. This is known as GIGO, or Garbage in Garbage Out.

5.2.3 OutputThe output stage of computing is concerned with giving out processed data as information in a form that is useful to the user. Output devices are used to do this. The most commonly used output devices are the screen, which is also called a monitor or VDU and the printer.

5.3 Architecture of Computer SystemThis is the ‘brain’ of the computer. It is where all the searching, sorting, calculating and decision making takes place. The CPU collects all of the raw data from various input devices (such a keyboard or mouse) and converts it into useful information by carrying out software instructions. The result of all that work is then sent to output devices such as monitors and printers.

The CPU is a microprocessor - a silicon chip - composed of tiny electrical switches called ‘transistors’. The speed at which the processor carries out its operations is measured in megahertz (MHz) or Gigahertz (GHz). The higher the number of MHz the faster the computer can process information. A common CPU today runs at around 3 GHz or more. The Intel Pentium processor and the Athlon are examples of a CPU.

PARTS OF A CPU

Inputs and Outputs

Control Unit

Backing Store

Immediate AccessStore

ARITHMETIC& LOGIC

UNIT(ALU)

Fig. 5.1 Block diagram of CPU

5.3.1 The Control Unit (CU)The Control Unit (CU) co-ordinates the work of the whole computer system and it has three main jobs:

It controls the hardware attached to the system. The Control Unit monitors the hardware to make sure that the • commands given to it by the current program are activated.It controls the input and output of data, so all the signals go to the right place at the right time.• It controls the flow of data within the CPU.•


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5.3.2 The Immediate Access Store (IAS)The Immediate Access Store (IAS) holds the data and programs needed at that instant by the Control Unit. The CPU reads data and programs kept on the backing storage and store them temporarily in the IAS’s memory. The CPU needs to do this because Backing Store is much too slow to be able to run data and programs from directly. For example, let’s pretend that a modern CPU was slowed down to carry out one instruction in 1 second, then the hard disk (i.e., Backing Store) would take 3 months to supply the data it needs! So the trick is to call in enough of the data and programs into fast Immediate Access Store memory so as to keep the CPU busy.

5.3.3 ALU stands for Arithmetic and Logic Unit.It is where the computer processes data by either manipulating it or acting upon it. It has two parts:

Arithmetic part - does exactly what you think it should - it does the calculations on data such as 3 + 2.• Logic part - This section deals with carrying out logic and comparison operations on data. For example working • out if one data value is bigger than another data value.

5.4 Concepts of FilesA computer file is a piece of arbitrary information, or resource for storing information, that is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished. Computer files can be considered as the modern counterpart of the files of printed documents that traditionally existed in offices and libraries.

5.4.1 File contentsAs far as the operating system is concerned, a file is in most cases just a sequence of binary digits. At a higher level, where the content of the file is being considered, these binary digits may represent integer values or text characters, It is up to the program using the file to understand the meaning and internal layout of information in the file and present it to a user as a document, image, song, or program. At any instant in time, a file has might have a size, normally expressed in bytes, that indicates how much storage is associated with the file.

Information in a computer file can consist of smaller packets of information (often called records or lines) that are individually different but share some trait in common. For example, a payroll file might contain information concerning all the employees in a company and their payroll details; each record in the payroll file concerns just one employee, and all the records have the common trait of being related to payroll this is very similar to placing all payroll information into a specific filing cabinet in an office that does not have a computer. A text file may contain lines of text, corresponding to printed lines on a piece of paper.

The way information is grouped into a file is entirely up to the person designing the file. This has led to a plethora of more or less standardised file structures for all imaginable purposes, from the simplest to the most complex. Most computer files are used by computer programs. These programs create, modify and delete files for their own use on an as-needed basis. The programmers who create the programs decide what files are needed, how they are to be used and (often) their names.

In some cases, computer programs manipulate files that are made visible to the computer user. For example, in a word-processing program, the user manipulates document files that she names herself. The content of the document file is arranged in a way that the word-processing program understands, but the user chooses the name and location of the file, and she provides the bulk of the information (such as words and text) that will be stored in the file.

Files on a computer can be created, moved, modified, grown, shrunk and deleted. In most cases, computer programs that are executed on the computer handle these operations, but the user of a computer can also manipulate files if necessary. For instance, Microsoft Word files are normally created and modified by the Microsoft Word program in response to user commands, but the user can also move, rename, or delete these files directly by using a file manager program such as Windows Explorer (on Windows computers).

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5.4.2 Operations on the fileThe operations which are performed on the file are as follows:

Opening a file to use its contents• Reading or updating the contents• Committing updated contents to durable storage• Closing the file, thereby losing access until it is opened again•

5.4.3 File OrganisationThere are various kinds of files and each has its own kind of orgnisation. These file organisations are explained below:Sequential FileAccess to records in a Sequential file is serial. To reach a particular record, all the preceding records must be read. As we observed when the topic was introduced earlier in the course, the organisation of an unordered Sequential file means it is only practical to read records from the file and add records to the end of the file (OPEN..EXTEND). It is not practical to delete or update records. While it is possible to delete, update and insert records in an ordered sequential file, these operations have some drawbacks.

Problems accessing ordered Sequential filesRecords in an ordered sequential file are arranged, in order, on some key field or fields. When we want to insert, delete or amend a record we must preserve the ordering. The only way to do this is to create a new file. In the case of an insertion or update, the new file will contain the inserted or updated record. In the case of a deletion, the deleted record will be missing from the new file.

The main drawback to inserting, deleting or amending records in an ordered sequential file is that the entire file must be read and then the records written to a new file. Since disk access is one of the slowest things we can do in computing this is very wasteful of computer time when only a few records are involved. For instance, if 10 records are to be inserted into a 10,000 record file, then 10,000 records will have to be read from the old file and 10,010 written to the new file. The average time to insert a new record will thus be very great.

Inserting records in an ordered Sequential fileTo insert a record in an ordered Sequential file:

All the records with a key value less than the record to be inserted must be read and then written to the new • file.Then the record to be inserted must be written to the new file.• Finally, the remaining records must be written to the new file.•

Deleting records from an ordered Sequential fileTo delete a record in an ordered Sequential file:

All the records with a key value less than the record to be deleted must be written to the new file.• When the record to be deleted is encountered it is not written to the new file.• Finally, all the remaining records must be written to the new file.•

Amending records in an ordered Sequential fileTo amend a record in an ordered Sequential file:

All the records with a key value less than the record to be amended must be read and then written to the new • file.Then the record to be amended must be read the amendments applied to it and the amended record must then • be written to the new file.Finally, all the remaining records must be written to the new file.•


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5.4.4 Relative FileAs we have already noted, the problem with sequential files is that access to the records is serial. To reach a particular record, all the proceeding records must be read. Direct access files allow direct access to a particular record in the file using a key and this greatly facilitates the operations of reading, deleting, updating and inserting records. COBOL supports two kinds of direct access file organisations -Relative and Indexed.

Organisation of Relative filesRecords in relative files are organised on ascending relative record number. A Relative file may be visualised as a one dimension table stored on disk, where the relative record number is the index into the table. Relative files support sequential access by allowing the active records to be read one after another.

RelativeRecordNumber

1 Rec001

2 free

3 Rec003

4 Rec004

5 free

6 free

7 Rec007

325 Rec325

326 Rec326

327 free

328 Rec328

Fig. 5.2 Relative File - Organisation

Relative files support only one key. The key must be numeric and must take a value between 1 and the current highest relative record number. Enough room is allocated to the file to contain records with relative record numbers between 1 and the highest record number.

For instance, if the highest relative record number used is 10,000 then room for 10,000 records is allocated to the file. Figure 1 below contains a schematic representation of a Relative file. In this example, enough room has been allocated on disk for 328 records. But although there is room for 328 records in the current allocation, not all the record locations contain records. The record areas labeled “free”, have not yet had record values written to them.

Accessing records in a Relative fileTo access a record in a Relative file a Relative Record Number must be provided. Supplying this number allows the record to be accessed directly because the system can use the start position of the file on disk, the size of the record, and the relative record number to calculate the position of the record.

Because the file management system only has to make a few calculations to find the record position the Relative file organisation is the faster of the two direct access file organisations available in COBOL. It is also the most storage efficient.

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5.4.5 Indexed FilesWhile the usefulness of a Relative file is constrained by its restrictive key, Indexed files suffer from no such limitation. Indexed files may have up to 255 keys, the keys can be alphanumeric and only the primary key must be unique. In addition, it is possible to read an Indexed file sequentially on any of its keys.

Organisation of Indexed filesAn indexed file may have multiple keys. The key upon which the data records are ordered is called the primary key. The other keys are called alternate keys. Records in the Indexed file are sequenced on ascending primary key. Over the actual data records, the file system builds an index. When direct access is required, the file system uses this index to find, read, insert, update or delete the required record.

For each of the alternate keys specified in an Indexed file, an alternate index is built. However, the lowest level of an alternate index does not contain actual data records. Instead, this level made up of base records which contain only the alternate key value and a pointer to where the actual record is. These base records are organised in ascending alternate key order. As well as allowing direct access to records on the primary key or any of the 254 alternate keys, indexed files may also be processed sequentially. When processed sequentially, the records may be read in ascending order on the primary key or on any of the alternate keys.

Since the data records are in held in ascending primary key sequence it is easy to see how the file may be accessed sequentially on the primary key. It is not quite so obvious how sequential on the alternate keys is achieved. This is covered in the unit on Indexed files.

Organizing files and floders

(root)

Payroll

Salaries

Logfile

Widgets

Foobar

Employees

Timecards

Managers

Leads

Clerks

Fig. 5.3 Files and folders arranged in a hierarchy

In modern computer systems, files are typically accessed using names. In some operating systems, the name is associated with the file itself. In others, the file is anonymous, and is pointed to by links that have names. In the latter case, a user can identify the name of the link with the file itself, but this is a false analogue, especially where there exists more than one link to the same file.


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Files (or links to files) can be located in directories. However, more generally, a directory can contain either a list of files, or a list of links to files. Within this definition, it is of paramount importance that the term “file” includes directories. This permits the existence of directory hierarchies. A name that refers to a file within a directory must be unique. In other words, there must be no identical names in a directory. However, in some operating systems, a name may include a specification of type that means a directory can contain an identical name to more than one type of object such as a directory and a file.

In environments in which a file is named, a file’s name and the path to the file’s directory must uniquely identify it among all other files in the computer system no two files can have the same name and path. Where a file is anonymous, named references to it will exist within a namespace. In most cases, any name within the namespace will refer to exactly zero or one file. However, any file may be represented within any namespace by zero, one or more names. Any string of characters may or may not be a well-formed name for a file or a link depending upon the context of application. Whether or not a name is well formed depends on the type of computer system being used. Early computers permitted only a few letters or digits in the name of a file, but modern computers allow long names (some up to 255) containing almost any combination of unicode letters or unicode digits, making it easier to understand the purpose of a file at a glance. Some computer systems allow file names to contain spaces; others do not. Such characters such as / or \ are forbidden. Case-sensitivity of file names is determined by the file system.

Most computers organise files into hierarchies using folders, directories, or catalogs. (The concept is the same irrespective of the terminology used.) Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as subfolders. Subfolders can contain still more files and folders and so on, thus building a tree-like structure in which one “master folder” (or “root folder” — the name varies from one operating system to another) can contain any number of levels of other folders and files. Folders can be named just as files can (except for the root folder, which often does not have a name). The use of folders makes it easier to organise files in a logical way.

5.5 Protecting FilesMany modern computer systems provide methods for protecting files against accidental and deliberate damage. Computers that allow for multiple users implement file permissions to control who may or may not modify, delete, or create files and folders. A given user may be granted only permission to modify a file or folder, but not to delete it; or a user may be given permission to create files or folders, but not to delete them. Permissions may also be used to allow only certain users to see the contents of a file or folder. Permissions protect against unauthorised tampering or destruction of information in files, and keep private information confidential by preventing unauthorised users from seeing certain files.

Another protection mechanism implemented in many computers is a read-only flag. When this flag is turned on for a file (which can be accomplished by a computer program or by a human user) the file can be examined, but it cannot be modified. This flag is useful for critical information that must not be modified or erased, such as special files that are used only by internal parts of the computer system. Some systems also include a hidden flag to make certain files invisible; this flag is used by the computer system to hide essential system files that users must never modify.

5.6 Storing filesIn physical terms, most computer files are stored on hard disks spinning magnetic disks inside a computer that can record information indefinitely. Hard disks allow almost instant access to computer files. On large computers, some computer files may be stored on magnetic tape. Files can also be stored on other media in some cases, such as writeable compact discs, Zip drives, etc.

5.6.1 Backing up filesWhen computer files contain information that is extremely important, a backup process is used to protect against disasters that might destroy the files. Backing up files simply means making copies of the files in a separate location so that they can be restored if something happens to the computer, or if they are deleted accidentally.

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There are many ways to back up files. Most computer systems provide utility programs to assist in the back-up process, which can become very time consuming if there are many files to safeguard. Files are often copied to removable media such as writeable CDs or cartridge tapes. Copying files to another hard disk in the same computer protects against failure of one disk, but if it is necessary to protect against failure or destruction of the entire computer, then copies of the files must be made on other media that can be taken away from the computer and stored in a safe, distant location.

5.7 File TerminologyThere are a few terms that you need to understand when learning about file system. These will be explained over the next couple of pages. File can store data or information in various formats. Suppose in a file data is stored in the tables just like the one below:

First Name Last Name Address City Age

Mickey Mouse 123 Fantasy Way Anaheim 73

Bat Man 321 Cavern Ave Gotham 54

Wonder Woman 987 Truth Way Paradise 39

Donald Duck 555 Quack Street Mallard 65

Bugs Bunny 567 Carrot Street Rascal 58

Wiley Coyote 999 Acme Way Canyon 61

Cat Woman 234 Purrfect Street Hairball 32

Tweety Bird 543 Itotltaw 28

Table 5.2 File terminology

5.7.1 RecordsAs you saw previously, each table stores can hold a great deal of data. Each table contains a lot of records. A record is all of the data or information about one person or one thing. In the table below, all of the information about each cartoon character is stored in a ‘row’ or record.










Records

Table 5.3 Records


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What information could you find in the record for Cat Woman?What do you think the database at your school stores records about?How about the library? What records would be stored on that database?

5.7.2 FieldsEach table contains a lot of records. A record is made up of lots of individual pieces of information. Look at Wonder Woman’s record; it stores her first name, last name, address, city and age. Each of these individual pieces of information in a record are called a ‘field’ A ‘field’ is one piece of data or information about a person or thing.

Fields










Table 5.4 Fields

What fields can you find about Tweety Bird?What fields do you think would be stored in your student record on the school database?What fields would be stored in a book record in the library database?

5.8 Data CapturingAny database or information system needs data entered into it, in order for it to be of any use. There are many methods which can be used to collect and enter data, some manual, and some automatic. We will also look in particular detail at designing an effective paper-based data capture form.

5.8.1 Direct Data CapturingHere are some of the methods that can be used to capture data directly.

Barcode readerA bar code reader uses visible red light to scan and ‘read’ the barcode. As the red light shines across the light and dark bands of the barcode, so the reflected red light is also lighter and darker (do you see that on the picture opposite?) The Hand Scanner senses the reflected light and translates it into digital data. The digital data is then input into the computer. The computer may display the results on a screen and also input it into the correct fields in the database. Typical uses:

Shop - to find details on the product sold and price• Library - record the ISBN number of the book and the borrower’s card number• Warehouse - to check the labels on boxes delivered against what is recorded on the delivery sheet.•

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Magnetic ink character recognition (MICR)The numbers at the bottom of a cheque are written in a special ink which contains iron particles. This ink is magnetised and commonly called ‘magnetic ink’. It can be read by a special machine called a Magnetic Ink Character Reader (MICR).

Optical mark readers (OMR)An Optical Mark Reader is a scanning device that reads carefully placed pencil marks on a specially designed form or document. A simple pen or pencil mark is made on the form to indicate the correct choice e.g. a multiple choice exam paper or on the National Lottery ticket selection form.

The completed forms are scanned by an Optical Mark Reader (OMR) which detects the presence of a mark by measuring the reflected light. Less light is reflected where a mark has been made. The OMR then interprets the pattern of marks into a data record and sends this to the computer for storage, analysis and reporting. This provides a very fast and accurate method of inputting large amounts of data, provided the marks have been made accurately and clearly.

Optical character recognition (OCR)Optical Character Recognition (OCR) enables the computer to identify written or printed characters. An OCR system consists of a normal scanner and some special software. The scanner is used to scan the text from a document into the computer. The software then examines the page and extracts the text from it, storing it in a form that can be edited or processed by normal word processing software. The ability to scan the characters accurately depends on how clear the writing is. Scanners have been improved to be able to read different styles and sizes of text as well as neat handwriting. Although they are often up to 95% accurate, any text scanned with OCR needs careful checking because some letters can be misread. OCR is also used to automatically recognise postcodes on letters at sorting offices.

Speech RecognitionThe user talks into a microphone. The computer ‘listens’ to the speaker, then translates that information to written words and phrases. It then displays the text on to the monitor. This process happens immediately, so as you say the words, they appear on the screen. The software often needs some “training” in order for it to get used to your voice, but after that it is simple to use.

5.8.2 Data Capture FormsAlthough there are many methods of capturing data automatically, many businesses prefer to capture it manually.

Paper-based data capture formsThis is the most commonly used method of collecting or capturing data. People are given a form to fill in with their personal details, e.g. name, address, telephone number, date of birth etc. Once the form is completed, it is given to a member of staff who will enter the data from it, into a database or information system.

Computerised data entry formsA member of staff could type the information directly into a computerised data entry form whilst the customer is with them. They ask the question in the order it appears on the form and enter the answer using a keyboard. More commonly though, the details will be typed in by copying what was written on the paper-based data capture form. When this method is used, it is important that the fields on both forms are laid out in the same order to speed up the process of entering the data.

Designing Data Capture FormA data capture form looks simple enough to design, don’t you just type out a few questions, put a couple of boxes for customers to fill in their information and then print it out? No, it’s not as simple as that. If you want to collect good quality data, you need to think carefully about the design of the form. All forms should have the name of the organisation at the top.


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GREYSIDE YOUTH CLUB

Memebership Application Form

Please complete the top section of this membership apliccation form. Then send the form to The Youth Club, 15 Greyside Park, Liverpool, Merseyside, L2 3XJ.

Fig. 5.4 Sample data capture form

They should also have an explanation to tell the customer what the form is for, in this case ‘membership application form’, or ‘data collection form’, or ‘customer details form’ or something similar. Lastly, they should give the customer instructions to tell them what they should do with the form once they have completed it. Here it tells the person filling the form in, to send it back to the address given.

Title: Mr Miss Tick one box Other (Please State Here: )

Travel Arrangement If the information is incorrect, please click the appropriate choice

Bicycle Train Bus Walks Car Coach Taxi Other Route

Dietary Needs

Meal Arrangement If the information is incorrect, please click the appropriate choice

Free school meal Paid school meal Sandwiches Home Other

Fig. 5.5 Form filled by the customer

Where possible, it is a good idea to try to limit the options that people can enter. If you can manage to do this, then you can set up your computerised system with a drop down box that gives all of the options on the form – making it faster for staff to enter the data. For Example: The first form shown above, limits the choice of title to ‘Mr’ or ‘Miss’. This is sufficient in this case because it is an application form for a childrens’ youth club, so it is unlikely that there will be any ‘Mrs’ or ‘Dr’ or ‘Reverend’

The second form gives people the different options for travel; they have to tick one of the options since there isn’t any room for them to write something different. The same method has been used for types of lunches.

5.9 VerificationIt was mentioned that validation cannot make sure that data you enter is correct, it can only check that it is sensible, reasonable and allowable. However, it is important that the data in your database is as accurate as possible. Have you ever heard of the term ‘Garbage in, garbage out’ or ‘GIGO’? This means that if you enter data that is full of mistakes (garbage in) then when you want to search for a record you will get data with mistakes presented to you (garbage out).

This is where Verification can help to make sure that the data in your database contains as few mistakes as possible. Verification means to check something twice. Think about when you choose a new password, you have to type it in twice. This lets the computer check if you have typed it exactly the same both times and not made a mistake. The data in your database can be verified or checked twice.

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FRUIT COLOUR SIZEApple Yellow MediumOrange Orange MediumStrawberry Red SmallBanana Yellow MediumCherry Red SmallGrape Green SmallMelon Yellow LargeBlacberry Black Small

This can be done in different ways:Somebody else can check the data on the screen for you against the original paper documents.• You could print out your table and check it against the original paper documents.• You could type in the data twice (like you do with your password), and get the computer to check that both sets • of data are identical.

Other methods of verification include control, batch or hash totals. To find out more about these, visit the mini-website on Validation and Verification.

5.9.1 Editing and CheckingAs well as choosing the correct data types to try to reduce the number of errors made when entering data into the database, there is another method that can be used when setting up the table. This is called ‘Validation’. It is very important to remember that Validation cannot stop the wrong data being entered, you can still enter ‘Smiht’ instead of ‘Smith’ or ‘Brown’ instead of ‘Green’ or ‘78’ instead of ‘87’.

What Validation can do, is to check that the data is sensible, reasonable and allowable. This page will not go into any great depth about different methods of validation as there is a whole mini-website on Validation alone. Go and have a look at it to find out more details about the best kind of Validation to use and the reasons why. Some of the types of Validation that you could set up for your database are:

Validation Example

Type CheckIf the datatype number has been chosen, then only that type of data will be allowed to be entered i.e. numbers.If a field is to accept certain choices e.g. title might be restricted to ‘Mr’, ‘Mrs’, ‘Miss’ and ‘Ms’ then ‘Dr’ wouldn’t be allowed.

2, 3, 4Mr, Mrs, Miss, MsBrown, Green, Blue, Yellow, Red


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Range CheckA shop may only sell items between the price of ₤ 10.00 and ₤ 50.00 . To stop mistakes being made, a range check can be set up to stop ₤500.00 being entered by accident.

A social club may not want people below the age of 18 to be able to join.

Notice the use of maths symbols:>‘greater than’< ‘less than’= ‘equals’

>=10 AND <=50

>=18

Presence CheckThere might be an important piece of data that you want to make sure is always stored. For example, a school will always want to know an emergency contact number, a video rental store might always want to know a customer’s address, a wedding dress shop might always want a record of the brides wedding date.

A presence check makes sure that a critical field cannot be left blank, it must be filled in.

School Database: Emergency contact number DVLA Database: Date test passedElectoral Database: Date of birthVet’s Database: Type of Pet

Picture or format checkSome things are always entered in the same format. Think about postcode, it always has a letter, letter, number, number, number, letter and letter e.g. CV43 9PB. There may be the odd occasion where it differs slightly e.g. a Birmingham postcode B19 8WR, but the letters and numbers are still in the same order.

A picture or format check can be set up to make sure that you can only put letters where letters should be and numbers where numbers should be.

Postcode: CV43 9PBTelephone Number (01926) 615432

Table 5.5 Types of validation

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SummaryData processing is any computer process that converts data into information.• A single datum is a single measurement from the real world.• Data are any facts, numbers, or text that can be processed by a computer.• Whenever a computer is used it must work its way through three basic stages before any task can be • completed.A program is a set of step-by-step instructions which tells the computer exactly what to do with the input in • order to produce the required output.The input stage of computing is concerned with getting the data needed by the program into the computer.• The most commonly used output devices are the screen, which is also called a monitor or VDU and the • printer.The CPU collects all of the raw data from various input devices (such a keyboard or mouse) and converts it into • useful information by carrying out software instructions.The Immediate Access Store (IAS) holds the data and programs needed at that instant by the Control Unit.• A computer file is a piece of arbitrary information, or resource for storing information, that is available to a • computer program and is usually based on some kind of durable storage.Information in a computer file can consist of smaller packets of information (often called records or lines) that • are individually different but share some trait in common.The programmers who create the programs decide what files are needed, how they are to be used and (often) • their names.Files on a computer can be created, moved, modified, grown, shrunk and deleted.• Records in an ordered sequential file are arranged, in order, on some key field or fields.• In the case of an insertion or update, the new file will contain the inserted or updated record.• Direct access files allow direct access to a particular record in the file using a key and this greatly facilitates the • operations of reading, deleting, updating and inserting records.A Relative file may be visualised as a one dimension table stored on disk, where the relative record number is • the index into the table.An indexed file may have multiple keys.• Most computers organise files into hierarchies using folders, directories, or catalogs.• Many modern computer systems provide methods for protecting files against accidental and deliberate • damage.

ReferencesThierauf, J. B. & Niehaus, F. J., 1980. • An introduction to data processing for business, Wiley.Micallef, A. B., 1971. • An introduction to data processing, Cummings Pub. Co.Kumar, V. & Kumar, D., • LESSON 1 INTRODUCTION TO DATA PROCESSING [Pdf] Available at: <http://www.ddegjust.ac.in/studymaterial/pgdca/ms-09.pdf> [Accessed 24 May 2013].2 Data Processing Concept• [Pdf] Available at: <http://download.nos.org/srsec330/330L2.pdf> [Accessed 24 May 2013].An Introduction to Data Visualization & Processing - Uttam Grandhi• [Video online] Available at: <http://www.youtube.com/watch?v=EC-8VxXJER4> [Accessed 24 May 2013].Dr. Garg, N., 2008. • Lecture - 1 Introduction to Data Structures and Algorithms [Video online] Available at: <http://www.youtube.com/watch?v=zWg7U0OEAoE> [Accessed 24 May 2013].


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Recommended ReadingRobichaud, B., Muscat, J. E. & Hall, A., 1977. • Introduction to Data Processing, 2nd ed. Greg Division, McGraw-Hill.Carver, K. D., 1974. • Introduction to data processing, John Wiley & Sons Australia, Limited.Harris, L. M., 1986. • Introduction to data processing: mainframes, minis, and microcomputers, 3rd ed. Wiley.

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Self Assessment___________ is defined as either a meaningful answer to a query or a meaningful stimulus that can cascade 1. into further queries.

Data processing a. Informationb. Datumc. Technologyd.

_________ are defined as numbers or characters that represent measurements from the real world.2. Dataa. Numbersb. Queriesc. Cellsd.

Match the following3.

Operational or transactional data1. NominalA.

Non-operational data2. Data about the data itselfB.

Meta data3. Forecast dataC.

Categorical data4. InventoryD.

1-A, 2-D, 3-C, 4-Ba. 1-B, 2-A, 3-D, 4-Cb. 1-D, 2-C, 3-B, 4-Ac. 1-C, 2-B, 3-A, 4-Dd.

The CPU is a microprocessor - a silicon chip - composed of tiny electrical switches called __________.4. transistorsa. megahertzb. microchipsc. processord.

Which of the following statements is false?5. The higher the number of MHz the faster the computer can process information.a. A common CPU today runs at around 3 GHz or more.b. The Intel Pentium processor and the Athlon are examples of a operating system.c. The speed at which the processor carries out its operations is measured in megahertz (MHz) or Gigahertz d. (GHz).


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A computer ________ is a piece of arbitrary information, or resource for storing information, that is available 6. to a computer program and is usually based on some kind of durable storage.

diska. storageb. digitc. filed.

__________ files allow direct access to a particular record in the file using a key and this greatly facilitates the 7. operations of reading, deleting, updating and inserting records.

Relative filea. Direct accessb. Sequential filec. Indexed filesd.

___________ may have up to 255 keys, the keys can be alphanumeric and only the primary key must be 8. unique.

Relative filea. Direct accessb. Sequential filec. Indexed filesd.

Any string of __________ may or may not be a well-formed name for a file or a link depending upon the context 9. of application.

charactersa. numbersb. symbolsc. datad.

What allows instant access to computer files?10. Magnetic tapea. Recordsb. Hard disksc. Fieldsd.

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Chapter VI

Operating Systems

Aim

The aim of this chapter is to:

introduce basic organisation of computer systems•

elucidate history of DOS•

discuss batch files and batch system•

Objectives

The objectives of this chapter are to:

explain spooling•

discuss essential properties of the operating system batch•

define operating system, functions, history and evolution•

Learning outcome

At the end of this chapter, you will be able to:

analyse multiprogramming•

explain time sharing system•

understand internal and external commands of DOS•


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6.1 IntroductionAn operating system acts as an intermediary between the user of a computer and computer hardware. The purpose of an operating system is to provide an environment in which a user can execute programs in a convenient and efficient manner. An operating system is software that manages the computer hardware. The hardware must provide appropriate mechanisms to ensure the correct operation of the computer system and to prevent user programs from interfering with the proper operation of the system.

6.2 Operating SystemAn Operating system is a program that controls the execution of application programs and acts as an interface between the user of a computer and the computer hardware. A more common definition is that the operating system is the one program running at all times on the computer (usually called the kernel), with all else being applications programs. An Operating system is concerned with the allocation of resources and services, such as memory, processors, devices and information. The Operating System correspondingly includes programs to manage these resources, such as a traffic controller, a scheduler, memory management module, I/O programs, and a file system.

6.2.1 Functions of Operating SystemOperating system performs three functions:

Convenience: An OS makes a computer more convenient to use.• Efficiency: An OS allows the computer system resources to be used in an efficient manner.• Ability to Evolve: An OS should be constructed in such a way as to permit the effective development, testing • and introduction of new system functions without at the same time interfering with service.

6.2.2 Operating System as User InterfaceEvery general purpose computer consists of the hardware, operating system, system programs and application programs. The hardware consists of memory, CPU, ALU, I/O devices, peripheral device and storage device. System program consists of compilers, loaders, editors, OS etc. The application program consists of business program, database program. The Figure shows the conceptual view of a computer system.

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user1

user2

user3

compiler assembler text editor databasesystem

system and application programs

operating system

Computer Hardware

usern

Fig. 6.1 Conceptual view of a computer system

Every computer must have an operating system to run other programs. The operating system coordinates the use of the hardware among the various system programs and application program for a various users. It simply provides an environment within which other programs can do useful work.

The operating system is a set of special programs that run on a computer system that allow it to work properly. It performs basic tasks such as recognising input from the keyboard, keeping track of files and directories on the disk, sending output to the display screen and controlling the peripheral devices. OS is designed to serve two basic purposes:

It controls the allocation and use of the computing system‘s resources among the various user and tasks.• It provides an interface between the computer hardware and the programmer that simplifies and makes feasible • for coding, creation, debugging of application programs.

The operating system must support the following tasks. The tasks are:Provides the facilities to create, modification of program and data files using and editor.• Access to the compiler for translating the user program from high level language to machine language.• Provide a loader program to move the compiled program code to the computer‘s memory for execution.• Provide routines that handle the details of I/O programming.•


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6.3 History of Operating SystemOperating systems have been evolving through the years. Following table shows the history of OS.

Generation Year Electronic devices used Types of OS and devices

First 1945 – 55 Vacuum tubes Plug boards

Second 1955 – 1965 Transistors Batch system

Third 1965 – 1980 Integrated Circuit (IC) Multiprogramming

Fourth Since 1980 Large scale integration PC

Table 6.1 History of OS

6.4 Disk Operating System Disk Operating System (specifically) and disk operating system (generically), most often abbreviated as DOS (not to be confused with the DOS family of disk operating systems for the IBM PC compatible platform), refer to operating system software used in most computers that provides the abstraction and management of secondary storage devices and the information on them (e.g., file systems for organising files of all sorts). Such software is referred to as a disk operating system when the storage devices it manages are made of rotating platters (such as hard disks or floppy disks).

In the early days of micro computing, memory space was often limited, so the disk operating system was an extension of the operating system. This component was only loaded if it was needed. Otherwise, disk-access would be limited to low-level operations such as reading and writing disks at the sector-level. In some cases, the disk operating system component (or even the operating system) was known as DOS. Sometimes, a disk operating system can refer to the entire operating system if it is loaded off a disk and supports the abstraction and management of disk devices. An example is DOS/360. On the PC compatible platform, an entire family of operating systems was called DOS.

6.4.1 History of DOS In the early days of computers, there were no disk drives; delay lines, punched cards, paper tape, magnetic tape, magnetic drums, were used instead. And in the early days of microcomputers, paper tape or audio cassette tape or nothing were used instead. In the latter case, program and data entry was done at front panel switches directly into memory or through a computer terminal / keyboard, sometimes controlled by a ROM BASIC interpreter; when power was turned off after running the program, the information so entered vanished.

Both hard disks and floppy disk drives require software to manage rapid access to block storage of sequential and other data. When microcomputers rarely had expensive disk drives of any kind, the necessity to have software to manage such devices (i.e., the disks) carried much status. To have one or the other was a mark of distinction and prestige, and so was having the Disk sort of an Operating System. As prices for both disk hardware and operating system software decreased, there were many such microcomputer systems.

6.4.2 Components of MS-DOSDOS is an Operating System. It works as an interpreter between user and computer. We give English like commands and it converts it into machine language and after the computer has processed the information, returns the results to you in English. Ms. Dos consist of four essential programs and a set of additional utilities.

MS-DOS consists of four essentials programs and a set of additional utilities. Four main programs are:Boot Record• IO.SYS• MSDOS.SYST• COMMAND.COM•

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Booting: Process that starts up a computer is called booting. It checks for proper functioning of all the peripheral devices attached with the system. It searches for the operating system and, when located, loads it into the main memory.

Cold Booting is done by turning on the computer.• Warm Booting is performed by pressing Ctrl+Alt+Del keys simultaneously.•

There are two name in DOS and is divided into 2 parts.Primary Name• Secondary or extension.•

Primary name is separated from the Secondary name extension with the help of a dot (.) look at the following example.

Example: ENVOICE. TXT

Primary name can be from 1 to 8 characters long and Secondary name contains 3 or less than 3 characters and is optional. The extension tells DOS about what kind of file it is. Valid Characters for naming a file are: from A to Z and the digit 0 to 9

C :\> Is known as DOS/command prompt, where we give the commands.

DOS command divided into 2 parts:Internal Commands or Memory-Resident Commands• External Command or Disk-Residence Commands•

6.4.3 Internal CommandThere are also called memory-resident commands. These commands are automatically loaded into the computer’s memory during the booting process. They actually included in the Command.com file. So these commands are executable immediately after getting the dos prompt. A few internal commands are:

VER• VOL• DATE • TIME • CLS• DIR• MD• CD• PATH• RD• COPY CON• TYPE • COPY• DEL• REN • PROMT•


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A command can be given in Capitals or Small letters also. The internal commands can execute immediately but External Commands require special files for their execution without which it is not possible to execute them.

VER: All O/S has its own edition number or release or version number. The version number indicates which edition of O/S you are working on.Syntax: VER <Enter>Example: C:\> Ver <Enter>Result will be: - Microsoft Windows XP [Version 5.1.2600]

VOL: It is used to display volume label and serial number of the current driveSyntax: Vol [drive:]Example: C:\> VOL

DATE: Used to display the current system date and prompt for entering new date.Syntax: Date <Enter>Example: C:\> date <Enter>

TIME: Displays the current system time and prompt for entering new time.Syntax: Time <Enter>Example: C:\> Time <Enter>

CLS: Clears the cluster screen.Syntax: CLS <Enter>Example: C:\> CLS <Enter>

DIR: This command displays the list of directories and files with details like date of creation whether it is directory or file etc.Syntax: DIR <Enter>Switches:/p : To view one screen of files at a time./w : Displays only five column of filenames and directories./b : Display only file and directory./l : Display all the information in lower case letters.

/a : stands for attributes that are given below/-h : Hidden (or not hidden) filess/-s : System (or not systems) filesd/-d : Directory (or not Directory) namesr/-r : Read only( or not read only) files

Example:DIR *.txt : Display all the files with extension .txtDIR D???.* : Display all the files starting with D and having less than or equal to four characters in the file name and any extension.

Here “?” And “*” are called “wild card character”“*” Stand for any number of the character“?” Stands for nay one character

MD OR MKDIR: Used to create a new Directory or nested DirectoriesSyntax: MKDIR OR MD [DRIVE:] PATH DIRECTORY NAMEExample: C:\> MD SAMS <Enter>

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CD OR CHDIR: This command allows changing present directory to another directory.Syntax: CD [DRIVE:] PATHExample: C:\> CD SAMS and press <Enter>

PATH: This command defines a list of directories DOS Searches for external commandsSyntax: PATH (Display the current Search Path)PATH; : ( Clear the search path so DOS will search for external commands only in the current directory)

RD: To delete the empty directory.Syntax: RD [DRIVE:] PATH

NOTE: The directory must be empty when we use RD.Example: C:\> RD SAMS and press <Enter>Switches /s – Remove with subdirectories and files./q – Don’t ask to confirm.

COPY CON: We use this command to create a new file.Syntax: COPY CON <FILENAME>Example: C:\> Copy Con sams.txt <Enter>Note: - Typing here and when you are done, press Ctr+Z or F6 key followed by Enter to save the current document.

TYPE: This command allows you to see the contents of an existing file on the screen.SYNTAX: TYPE <file name>Example: C:\> TYPE SAMS

COPY: Using this command you can make duplicate files of an existing file from one location to another or one directory to another with different name or exiting name.

SYNTAX: COPY < SOURCE FILE NAME> <TARGET FILENAME>Example: C:\> COPY SAMS.TXT A:\TAJExample: C:\> COPY*.TXT +*.BAK TARGET FILENAME And Then Press EnterExample: C:\> COPY SAMS.TXT C:\SAMS_1\FO\RECEPTION And Then Press Enter

You can also have the option to change the name of files as you copy it.Example: C:\> COPYold.TXT C:\dos\new.txt And Then Press Enter

DEL/ERASE: This command removes one or more files from the disk or current working directories. SYNTAX: DEL filespec [/p] or ERASE filespec [/p]Example: C:\> DEL C:*.BAK /P And Then Press EnterExample: C:\> DEL abc And Then Press EnterExample: C:\> DEL ????.COM And Then Press EnterSwitches /p –confirmation/q – In quit mode

REN: Used to change the name of the file or directory.SYNTAX: REN <file name>Example: REN sams sams1 <Enter>Example: REN *.dat *.mst And Then Press Enter

PROMPT: This command allows you to customise the dos promptSYNTAX: 1. PROMPT


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Character Example Description

$Q = Equal Sign

$$ $ Dollar Sign

$t 12:30:06:92 Display current time

$ d tue 09-07-2007 Display current date

$v msdos version 6.2 show dos version number

$g > Greater than sign

$L < Less than sign

Table 6.2 Some Special $ Parameters Are Given Below

Most people like to set their prompt to $p$g which display the current directory followed by > sign.Example: PROMPT $P$G <Enter>

TREE: It is used to display directory structure of a specified directory graphicallySyntax : TREE [drive:] [path] [/f][/F] : displays the names of the files in each directory

6.4.4 External CommandsThese are also called Disk-Resident Commands. These commands are meant for special purpose. These are found in separate files on Hard Disk or Floppy Disk, So that they don’t typically consume valuable memory space. They are loaded into memory only when called. Some External Commands are:

Xcopy• Move• FC• Doskey• Mem• FILTER•

More �Sort �Find �

Attrib• Deltree• Edit• Tree•

XCOPYThis command is faster than Copy Command and allows you to copy entire directories/disk including all the sub directories and files to destination.

Syntax : XCOPY Source [Target][/Y][-Y] [/P][/E]

SWITCHES:/-Y : Prompts before copying over existing files.

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/y : Overwrites existing files without prompting./p : Ask before copying each file./e : Copying empty directory also./s : Copying subfolders.

EXAMPLE: XCOPY C:\SAMS D:\SAMS /S/E

MOVEThis command moves a file or group of files from one directory to another and also one disk to another disk. It can also be used to rename directories.

Syntax: Move [Path File Name] [Destination file name path]

Swiches: /-Y : Prompt before it overwrites while it copies file that already exists./Y : Overwrites existing files without prompting.

EXAMPLE: move c:\sams\fo.txt to d:EXAMPLE: move c:\sams\fo.txt to d:\ new_sams

FCStands for File Compare. If you wish to compare two files or two sets of files then you may use this command. This command has the capability to differentiate between the files and display the difference.

Syntax: FC <files spec 1> <files spec2> [/a][/b][/c][l][/n]

Switches/a : This switch displays only the first and last line of each group./b : Compare the files in library mode ( byte-by-byte)/c : Ignore the case of letters./l : Compare the files in text mode./n : Displays the line number for lines that are different.

EXAMPLE: FC first.txt second.txt\n and then Press <enter>

DOSKEYDos can remember only the last command you had entered. But in order to make DOS remember all the commands you enter you will have to load a DOSKEY utility. Also Used To Create MacrosSyntax: DOSKEY and Press <Enter>Display message on the screen.DOSKEY Installed.

NOTE :To display all commands from the history list one the screen.

Example: DOSKEY / History or /h < Enter>.

Now when DOSKEY is in memory, it can help store all the commands which you enter so that any of those commands need not be typed again to be executed. And this all are called HISTORY LIST. Now when you want the same command to be done you can use right arrow key or ‘F1’ or ‘F3’ Issuing following command.

Second feature of DOSKEY is Doskey Macro. Using this macro you can create own command and latter you can run it on the system prompt.

For example “EXAMPLE: - DOSKEY C= CLS”


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Now if you type at the system prompt only C and press enter it will clear the screen.

Recalling Commands: Some key is provided to recall recent commands you have run since installing DOSKEY

Key Strok EffectUp Arrow Display the Preceding Command and further list.Down Arrow Show the next command you executed after the one that’s being displayedPage Up Display the oldest command that is still in DoskeyPage Down Show the most recent command that you executedF7 Display the entire list of command that you executedF9 Selects a commandAlt+F7 Erase the command history list.Alt+F10 Erase all macros in memoryEsc Clear the command line.Ctrl-T Command separator

6.5 UNIXUNIX is one of the very oldest operating systems in the computer world, and is still widely used today. However, it is not a very conspicuous operating system. Somewhat arcane in its operation and interface, it is ideally suited for the needs of large enterprise computing systems. It is also the most common operating system run by servers and other computers that form the bulk of the Internet. While you may never use UNIX on your local PC, you are using it indirectly, in one form or another, every time you log on to the ‘net.

While few people run UNIX on their own systems, there are in fact a number of different versions of UNIX available for the PC, and millions of PC users have chosen to install “UNIX” operating systems on their own desktop machines. There are dozens of variants of the basic UNIX interface; the most popular one for the PC platform is Linux, which is itself available in many flavors. While UNIX operating systems can be difficult to set up and require some knowledge to operate, they are very stable and robust, are efficient with system resources and are generally free or very inexpensive to obtain.

UNIX operating systems are designed to use the “UNIX file system”. The phrase is in quotes, because there is no single UNIX file system, any more than there is a single UNIX operating system. However, the file systems used by most of the UNIX operating system types out there are fairly similar, and rather distinct from the file systems used by other operating systems, such as DOS or Windows.

As an operating system geared specifically for use on the PC, Linux is the UNIX variant that gets the most attention in PC circles. To improve its appeal, the programmers who are continually working to update and improve Linux have put into the operating system compatibility support for most of the other operating systems out there. Linux will read and write to FAT partitions, and with newer versions this includes FAT32.

6.5.1 MEMThis command displays amount of total available memory (low, Expanded and Extended) and all currently programs.Syntax: MEM [/f][/p][/m]

Switches:/f : Using this switch MEM display all the areas of memory that are fee./p : Use this option to display the information one screen at a time./m : Display information about how a specified program is using memory.

Example: MEM/p and then press <Enter>

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6.5.2 FILTERA Powerful feature of DOS is its use of filters to process data directly. A DOS FILTER can process in unique way any data that passes through it and can change what we see on the screen.

There are three FILTERS include in DOS.MORE: More command used to pause vertical Scrolling on the display screen, after each screenful, The display • pauses and the message - - More - - appears. Pressing any key displays the next screen.EXAMPLE: C:\> MORE < TYPE FILE.TXT and then press <Enter>EXAMPLE: C:\> DIR /MORE and then press <Enter>SORT: Reads, Sorts in Order and sends the data to the screen, file or to another device. Sort to arrange data in • an order.SYNTAX: SORT [drive:][Path][filename][/r][+n]

Switches: [drive:][Path][filename] : Specifies the name and location of the file to be searches. It must be preceded by the redirection character (<).[/r] : Sort lines in reverse ASCII Order ( Z-A)[+n] : Sorts line starting with the contents in column n. The default is 1.

EXAMPLE: C:\> SORT < NAME .TXT and then press <Enter>EXAMPLE: C:\> SORT /+20 < PHONE .TXT and then press <Enter>EXAMPLE: C:\> DIR / SORT > PHONE .TXT and then press <Enter>

Note: Sort command doesn’t distinguish between upper and lower case. It can sort file of maximum 63 k size.Combining Input & Output redirection:EXAMPLE: C:\> SORT < NAME .DAT > SORTNAME.DAT and then press <Enter>Here the sort command is being directed to take its input from <name.dat and after sorting, send its output to the > sortname.dat file.

FIND: The find Filter is used to search a file one or more designated character (called a text string) Depending • upon the form of the FIND Command. Each line having (or not having) the text string is sent to an output devices. Such as the Screen, a file or the printer. The text string is always typed within quotes (“Text Sring”).SYNTAX: FIND [/v][/c][/n] “String “ [d:] [path][filename]Switches: [/v] : Displays all the lines that do not contain string.[/c] : Display the total number of lines found to contain the string.[/n] : Display the line number as well as the line that contains the string.[/i] : Ignores uppercase or lowercase during the search.

Where:“String” : Specifies one or more alphabet or numeric character whose maximum length should not be more than 250 characters and must be enclosed in double quotes.

[d:] [path][filename]: Specifies the name and location of the file to be searches EXAMPLE: C : \ > FIND “Rajni” my.txt per.txt and then press <Enter>EXAMPLE: C:\> DIR/ FIND “TXT” and then press <Enter>


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6.5.3 ATTRIBEvery File on the Disk has its own description like size, space occupied, the type, the date it was created, etc. Likewise, every file has few attributes. The attributes of a file indicates whether it is a

Read-Only File: r• Archive File a• Hidden File: h• System File s•

With the ATTRIB command you can check the attributes of a file.SYNTAX: ATTRIB [+r][+a][+h][/+s] [filename]Switches:+r, -r : +r Read-Only attribute or, -r turn of Read-Only attribute+a,-a : +a archive attribute, or -a turn of archive attribute+h,-h : +h hidden attribute, or –h turn of hidden attribute+s, -s : +s system attribute and it should not be used generally

Note: While Creating a new file every file gets read only attribute and archive attribute by default.

EXAMPLE: C:\> ATTRIB my.txt +R and then press <Enter>EXAMPLE: C:\> ATTRIB my.txt +H and then press <Enter>

6.5.4 DELTREEThis command used for deleting an entire directory whether in that directory contains files or subdirectories and also it will delete hidden files.Syntax: DELTREE [drive:][path] directories [/y]EXAMPLE: C:\> DELTREE my.txt and then press <Enter>

6.5.5 EDITThis is the DOS Editor, which you can use to edit the text file and also creating new file.Syntax: Edit [drive:][path][filename]EXAMPLE: C:\> EDIT c:\sams\FO.TXT and then press <Enter>EXAMPLE: C:\> Edit NEW FILE and then press <Enter>

6.6 Batch FilesIt is a collection of DOS commands to perform a certain task or a batch file is nothing but sequence of commands to perform sequence of operations step by step. Look at the following commands you give step by step to perform an operation.

Suppose your job isFirst - Check the directorySecond - Copy a file called ABC.txt to another diskThird - Delete ABC.TXT from the present diskFourth - Clear the screen

If you do all this steps daily after your hour, then the commands you give would be:C:\> DIR <Enter>• C:\> COPY C:ABC.TXT D: <Enter>• C:\> DEL ABC.TXT <Enter>• C:\> CLS <Enter>•

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Instead of heating your head daily giving the same set of commands you can do it in a much simpler manner. All you do is put all the commands in a batch file.

How to create a batch file:C:\> COPY CON A.bat <Enter>

Note: Here Con means Console that is Keyboard, A the file name and .bat is extension.

It is compulsory that a batch file must have extension .BAT. You will find the cursor below ‘A’ now typeC:\> DIR <Enter>C:\> COPY A.TXT D : <Enter>C:\> DEL A.TXT <Enter>C:\> CLS <Enter>

Now Press the F6 or Ctrl+Z key combination. You shall find ^Z symbol below CLS, Now press Enter. You will receive the following message: 1files Copied.

And you are returned to the prompt C:\>

Now to execute the Batch File simply type the name of the file. C:\> A <Enter>

You will see all the commands in the A.Bat come right into action. So instead of typing all those command one after another performed the same job by just typing the file name.

6.7 Batch SystemSome computer systems only did one thing at a time. They had a list of the computer system may be dedicated to a single program until its completion, or they may be dynamically reassigned among a collection of active programs in different stages of execution. Batch operating system is one where programs and data are collected together in a batch before processing starts. A job is predefined sequence of commands, programs and data that are combined in to a single unit called job.

Fig. 6.1 shows the memory layout for a simple batch system. Memory management in batch system is very simple. Memory is usually divided into two areas: Operating system and user program area.

Operating System

User Program Area

Resident Portion

Transient

Program

Fig. 6.2 Memory layout for a simple batch system


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Scheduling is also simple in batch system. Jobs are processed in the order of submission, i.e., first come first served fashion. When job completed execution, its memory is releases and the output for the job gets copied into an output spool for later printing. Batch system often provides simple forms of file management. Access to file is serial. Batch systems do not require any time critical device management.

Batch systems are inconvenient for users because users can not interact with their jobs to fix problems. There may also be long turnaround times. Example of this system is id generating monthly bank statement. Advantages of batch system are as follows:

Move much of the work of the operator to the computer.• Increased performance since it was possible for job to start as soon as the previous job finished.•

Disadvantages of batch systemTurnaround time can be large from user standpoint.• Difficult to debug program.• A job could enter an infinite loop.• A job could corrupt the monitor, thus affecting pending jobs.• Due to lack of protection scheme, one batch job can affect pending jobs.•

6.8 Time Sharing SystemsMulti-programmed batched systems provide an environment where the various system resources (for example, CPU, memory, peripheral devices) are utilised effectively. Time sharing, or multitasking, is a logical extension of multiprogramming. Multiple jobs are executed by the CPU switching between them, but the switches occur so frequently that the users may interact with each program while it is running.

An interactive, or hands-on, computer system provides on-line communication between the user and the system. The user gives instructions to the operating system or to a program directly, and receives an immediate response. Usually, a keyboard is used to provide input, and a display screen (such as a cathode-ray tube (CRT) or monitor) is used to provide output. If users are to be able to access both data and code conveniently, an on-line file system must be available. A file is a collection of related information defined by its creator. Batch systems are appropriate for executing large jobs that need little interaction.

Time-sharing systems were developed to provide interactive use of a computer system at a reasonable cost. A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer; each user has at least one separate program in memory. A program that is loaded into memory and is executing is commonly referred to as a process. When a process executes, it typically executes for only a short time before it either finishes or needs to perform I/O. I/O may be interactive; that is, output is to a display for the user and input is from a user keyboard. Since interactive I/O typically runs at people speeds, it may take a long time to complete.

A time-shared operating system allows the many users to share the computer simultaneously. Since each action or command in a time-shared system tends to be short, only a little CPU time is needed for each user. As the system switches rapidly from one user to the next, each user is given the impression that she has her own computer, whereas actually one computer is being shared among many users.

Time-sharing operating systems are even more complex than are multi-programmed operating systems. As in multiprogramming, several jobs must be kept simultaneously in memory, which requires some form of memory management and protection.

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6.9 MultiprogrammingWhen two or more programs are in memory at the same time, sharing the processor is referred to the multiprogramming operating system. Multiprogramming assumes a single processor that is being shared. It increases CPU utilisation by organising jobs so that the CPU always has one to execute. Fig. 4.3 shows the memory layout for a multiprogramming system.

Operating System

job 1

job 2

job 3

job 4

0

512M

Fig. 6.3 Memory layout for a multiprogramming system

The operating system keeps several jobs in memory at a time. This set of jobs is a subset of the jobs kept in the job pool. The operating system picks and begins to execute one of the jobs in the memory. Multi-programmed system provides an environment in which the various system resources are utilised effectively, but they do not provide for user interaction with the computer system.

Jobs entering into the system are kept into the memory. Operating system picks the job and begins to execute one of the jobs in the memory. Having several programs in memory at the same time requires some form of memory management. Multiprogramming operating system monitors the state of all active programs and system resources. This ensures that the CPU is never idle unless there are no jobs.

AdvantagesHigh CPU utilisation.• It appears that many programs are allotted CPU almost simultaneously.•

DisadvantagesCPU scheduling is requires.• To accommodate many jobs in memory, memory management is required.•


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6.10 SpoolingSpooling is an acronym for simultaneous peripheral operations on line. Spooling refers to putting jobs in a buffer, a special area in memory or on a disk where a device can access them when it is ready. Spooling is useful because device access data that different rates. The buffer provides a waiting station where data can rest while the slower device catches up. Fig 2.3 shows the spooling.

DISK

CARD READER PRINTER

Fig. 6.4 Spooling

Computer can perform I/O in parallel with computation; it becomes possible to have the computer read a deck of cards to a tape, drum or disk and to write out to a tape printer while it was computing. This process is called spooling.

The most common spooling application is print spooling. In print spooling, documents are loaded into a buffer and then the printer pulls them off the buffer at its own rate. Spooling is also used for processing data at remote sites. The CPU sends the data via communications path to a remote printer. Spooling overlaps the I/O of one job with the computation of other jobs. One difficulty with simple batch systems is that the computer still needs to read the decks of cards before it can begin to execute the job. This means that the CPU is idle during these relatively slow operations. Spooling batch systems were the first and are the simplest of the multiprogramming systems.

Advantage of SpoolingThe spooling operation uses a disk as a very large buffer.• Spooling is however capable of overlapping I/O operation for one job with processor operations for another • job.

6.11 Essential Properties of the Operating System BatchJobs with similar needs are batched together and run through the computer as a group by an operator or automatic job sequencer. Performance is increased by attempting to keep CPU and I/O devices busy at all times through buffering, off line operation, spooling and multiprogramming. A Batch system is good for executing large jobs that need little interaction; it can be submitted and picked up latter.

6.11.1 Time SharingIt uses CPUs scheduling and multiprogramming to provide economical interactive use of a system. The CPU switches rapidly from one user to another, i.e., the CPU is shared between a numbers of interactive users. Instead of having a job defined by spooled card images, each program reads its next control instructions from the terminal and output is normally printed immediately on the screen.

6.11.2 InteractiveUser is on line with computer system and interacts with it via an interface. It is typically composed of many short transactions where the result of the next transaction may be unpredictable. Response time needs to be short since the user submits and waits for the result.

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6.11.3 Real time systemReal time systems are usually dedicated, embedded systems. They typically read from and react to sensor data. The system must guarantee response to events within fixed periods of time to ensure correct performance.

6.11.4 DistributedIt distributes computation among several physical processors. The processors do not share memory or a clock. Instead, each processor has its own local memory. They communicate with each other through various communication lines.


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SummaryAn operating system acts as an intermediary between the user of a computer and computer hardware.• An operating system is software that manages the computer hardware.• An Operating system is concerned with the allocation of resources and services, such as memory, processors, • devices and information.Every general purpose computer consists of the hardware, operating system, system programs and application • programs.In the early days of micro computing, memory space was often limited, so the disk operating system was an • extension of the operating system.In the early days of computers, there were no disk drives; delay lines, punched cards, paper tape, magnetic tape, • magnetic drums, were used instead.DOS is an Operating System. It works as an interpreter between user and computer.• Process that starts up a computer is called booting.• The internal commands can execute immediately but External Commands require special files for their execution • without which it is not possible to execute them.Dos can remember only the last command you had entered.• UNIX is one of the very oldest operating systems in the computer world, and is still widely used today.• As an operating system geared specifically for use on the PC, Linux is the UNIX variant that gets the most • attention in PC circles.Batch operating system is one where programs and data are collected together in a batch before processing • starts.A job is predefined sequence of commands, programs and data that are combined in to a single unit called • job.Multi-programmed batched systems provide an environment where the various system resources (for example, • CPU, memory, peripheral devices) are utilised effectively.An interactive, or hands-on, computer system provides on-line communication between the user and the • system.Time-sharing systems were developed to provide interactive use of a computer system at a reasonable cost.• When two or more programs are in memory at the same time, sharing the processor is referred to the • multiprogramming operating system.Spooling is useful because device access data that different rates.•

ReferencesBhatt, C. P., 2003. • An Introduction to Operating Systems: Concepts and Practice, 3rd ed. PHI Learning Pvt. Ltd.Kifer, M. & Smolka, S., 2007. • Introduction to Operating System Design and Implementation: The OSP 2 Approach, Springer.DISK OPERATING SYSTEM (DOS)• [Pdf] Available at: <http://computerbabu.webs.com/-%20New%20Folder/DISK%20OPERATING%20SYSTEM%20(DOS).pdf> [Accessed 22 May 2013].Bhor, H., Rote, U. & Shinde, U., • Operating System [Pdf] Available at: <http://mu.ac.in/myweb_test/MCA%20study%20material/OS%20-%20PDF.pdf> [Accessed 22 May 2013].Murphy, M., 2011. • Introduction to Operating Systems [Video online] Available at: <http://www.youtube.com/watch?v=MzVGL44eq9w> [Accessed 22 May 2013].Learn Introduction to O S from the Fundamentals of Operating Systems• [Video online] Available at: <http://www.youtube.com/watch?v=cP-OPjwag4E> [Accessed 22 May 2013].

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Recommended ReadingBhatt, 2007. • Introduction To Operating Systems: Concepts And Practice An 2Nd Ed., 2nd ed. PHI Learning Pvt. Ltd.Johnson, P., 2004. • Introduction To Operating Systems, iUniverse.Jaeger, T., 2008. • Operating Systems Security, Morgan & Claypool Publishers.


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Self AssessmentAn ___________ is a program that controls the execution of application programs and acts as an interface 1. between the user of a computer and the computer hardware.

Operating systema. Hardwareb. Softwarec. Functiond.


MS-DOS1. Turning on the computerA.

Cold Booting2. Ctrl+Alt+DelB.

Warm Booting3. COMMAND.COMC.

Secondary name4. 3 or less than 3 charactersD. 1-A, 2-D, 3-B, 4-Ca. 1-C, 2-A, 3-B, 4-Db. 1-B, 2-C, 3-A, 4-Dc. 1-D, 2-B, 3-C, 4-Ad.

Which of the following sentences is false?3. A command can be given in Capitals or Small letters also.a. All O/S has its own edition number or release or version number.b. The internal commands can execute immediately but External Commands require special files for their c. execution without which it is not possible to execute them.DIR is used to display volume label and serial number of the current drive.d.

________ displays the current system time and prompt for entering new time.4. DATEa. TIMEb. CLSc. DIRd.

_________ command allows changing present directory to another directory.5. MKDIRa. PATHb. CHDIRc. RDd.

Which command is used to make duplicate files of an existing file?6. CUTa. COPYb. PASTEc. DUPLICATEd.

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ERASE1. Display directory structure of a specified directory graphicallyA.

REN2. Customise the dos promptB.

PROMPT3. Change the name of the file or directoryC.

TREE4. Removes one or more files from the disk or current working directoriesD. 1-B, 2-A, 3-C, 4-Da. 1-A, 2-B, 3-D, 4-Cb. 1-D, 2-C, 3-B, 4-Ac. 1-C, 2-D, 3-A, 4-Bd.

Which of the followings is not an external command?8. FCa. Doskeyb. Memc. VERd.

Which of the followings is not an internal command?9. COPY CONa. TYPE b. FILTERc. DELd.

_________ command displays amount of total available memory (low, Expanded and Extended) and all currently 10. programs.

MEMa. FILTERb. ATTRIBc. DELTREEd.


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Chapter VII

Internet and Network Security

Aim


explain internet’s workflow•

elucidate the different threats, consequences and remedies for network security•

explicate the concept of IP address •

Objectives


explain the role of TCP/IP in internet architecture•

enlist the types of threats to network security•

explain different options for optimum network security•

Learning outcome


identify and list key internet architecture components•

understand possible threats to the network security•

describe types of measures useful for network security maintenance•

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7.1 InternetInternet is the world's largest network. It is a unique collection of networks of different kinds. It is often described as “a network of networks” since all the smaller networks are linked together into one giant network called the Internet.

The use of internet began in 1969 in the U.S. Department of Defence’s Advanced Research Project Agency (ARPA) to provide immediate communication within the department during war. Computers were then installed at U.S. universities with defence related projects. As scholars began to go online, the network changed from military use to scientific use.

As Arpanet grew, administration of the system became distributed to a number of organisations, including the National Science Foundation (NSF). This shift of responsibility began the transformation of the science oriented Arpanet into the commercially minded and funded internet, which is used by millions today.

7.2 Internet ArchitectureInternet has a set architecture which is the basis of its functioning. We need to understand some basic concepts, and terminologies to understand internet better.

7.2.1 ProtocolArchitecture is based in the very specification of the standard TCP/IP protocol, designed to connect any two networks which may be very different in internal hardware, software, and technical design. Once two networks are interconnected, communication with TCP/IP is enabled end-to-end, so that any node on the internet has the ability to communicate with any node irrespective of their location. TCP/IP protocol has been discussed in detail in the earlier chapter.

7.2.2 IP Address Every computer on the internet has a unique numerical address, called an Internet Protocol (IP) address, used to route packets across the Internet. Just as a postal address enables the postal system to send mail to the desired destination from anywhere around the world, the computer's IP address gives the internet routing protocols the unique information they need to route packets of information to the computer from anywhere across the Internet. If a machine needs to contact another by a domain name, it first looks up for the corresponding IP address with the domain name service. The IP address is the geographical descriptor of the virtual world, and the addresses of both source and destination systems are stored in the header of every packet that flows across the Internet.

7.2.3 Domain Name ServiceThe Domain Name System (DNS), as a whole, consists of a network of servers that map internet domain names to a local IP addresses. The DNS enables domain names to stay constant while the underlying network topology and IP addresses change. This provides stability at the application level while enabling network applications to find and communicate with each other using the IP no matter how the underlying physical network changes.

7.2.4 Packet SwitchingThe key idea of packet switching is the division of each communication into individual, equal-sized packets. These packets are then sent individually to their destination through the network, and the entire message is reassembled when all the packets arrive. There are a range of procedures for retransmission of packets that might get lost in the network. On the internet, a typical packet length is about one kilobyte, or a thousand characters. A large message may be divided into thousands of individual packets. The beginning of a packet is called the ‘header’ and it records the following information:

Source: the IP address of the computer sending the packet• Destination: the IP address of the destination computer• Length: the length of the packet in bytes• Number: total number of packets in the complete message• Sequence: the number of this packet in the whole list of packets making up this communication.•


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This data provides the information that an internet router needs to get packets and messages to their destination. For additional reliability, internet packet headers also contain an error correction code, which is a number representing a mathematical combination of the rest of the packet data. If even a single bit of the packet is changed in transmission, then recalculation of the error correction code by a router won't match the code transmitted with the message, and the packet will be discarded and a request made for retransmission.

7.2.5 Internet RoutersInternet routers are specialised computers that interconnect the network by switching communications from one line to another at cross points. When a computer communicates with another on the internet, it addresses each packet with the other computer's IP address and then sends it to the closest internet router. The router then uses a routing algorithm to send the packet across the internet to the destination computer.

7.2.6 BackbonesBackbones are typically fibre optic trunk lines. The trunk line has multiple fibre optic cables combined together to increase the capacity. Fibre optic cables are designated OC for optical carrier, such as OC-3, OC-12 or OC-48. An OC-3 line is capable of transmitting 155 Mbps while an OC-48 can transmit 2,488 Mbps (2.488 Gbps). Connecting all the hardware, protocols and technologies, we have the internet serving millions of users. But the security of the data transferred, communications using the internet is a big question which needs to be addressed.

7.3 Network SecurityA good firm may face potential threats through internet or networking and the protective measures are essential for securing modern business network and IT infrastructure. Although the knowledge of threats and protective methods will not stop all attempts at network incursion or system attack, it can empower to eliminate certain general problems, greatly reducing the potential damages, and quickly detect breaches. With the ever-increasing number and complexity of attacks, vigilant approaches to security in both large and small enterprises are a must.

7.3.1 Understanding Potential ThreatsThreats can come from both internal and external sources. They may be human based, automated or even non intentional natural phenomenon. Their consequences differ as per the type of virus, type of attack, etc. We will have a brief view of the threats and consequences.

Threats Internal/External Consequences

e-mail with virus(viruses are explained after the table)

External origination, internal use

Could infect system reading email and subsequently spread throughout entire organisation.

Network with virus External Could enter through unprotected ports, compromise whole network.

Web based virus Internal browsing to external site

Could cause compromise on system doing browsing and subsequently affect other internal systems.

Web server attack External to web servers

If web server is compromised hacker could gain access to other systems internal to network.

Denial of service attack External External services such as web, email and file transfer protocol could become unusable

If router is attacked, whole network could go down.

Network user attack Internal to anywhere Firewalls do nothing for this attack. Internal segmentation firewalls can help contain damage.

Table 7.1 Types of threats and consequences.(Source: http://www.ptsdcs.com/whitepapers/70.pdf)

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Viruses A computer virus is a self-replicating computer program that behaves like a biological virus. It spreads by • inserting copies into other executable code or documents. Similar to the biological virus, it spreads on its own by multiplying itself throughout the system. There are • different types of viruses, prominent being Trojan horses, worms, and email viruses. The Trojan horses are computer programs which pretend to do one thing but actually do damage when they • start it. The worms viruses are pieces of software that use computer networks and security flaws to create copies of • self. A copy of the worm will then scan the network for any other machine that has a specific security flaw, and then replicate itself to the new machine.With regards to email viruses, these use email messages, and usually will copy and automatically mail itself to • hundreds of people.

7.3.2 Steps towards SecurityAntivirus Software

Antivirus software scans your PC for signatures of a virus. A virus signature is the unique part of that virus. It • can be a file name, how the virus behaves or the size of the virus file itself. Good antivirus software will find viruses that haven't yet infected PC and eliminate the ones that have already • attacked. Antivirus software can only protect your computer from viruses trying to infect via email, CD-Rom, floppy • disk, Word documents or other types of computer files. Antivirus software alone will not keep computer 100% safe and use firewall software is also necessary.

FirewallsA firewall is a mechanism by which a controlled barrier is used to control network traffic into and out of an • organisational intranet. Firewalls are basically application specific routers. They run on dedicated embedded systems such as an internet • appliance or they can be software programs running on a general server platform. In most cases these systems will have two network interfaces, one for the external network such as the internet • and one for the internal intranet side. The firewall process can tightly control what is allowed to traverse from one side to the other. Firewalls can range from being fairly simple to very complex. As with most aspects of security, deciding what • type of firewall to use will depend upon factors such as traffic levels, services needing protection and the complexity of rules required. The greater the number of services that must be able to traverse the firewall the more complex the requirement becomes.The difficulty for firewalls is distinguishing between legitimate and illegitimate traffic. Even private networks are • insecure due to the increased attacks and threats to the networks such as worms, viruses and clever hackers. Securing all equipment, including physical infrastructure equipment such as UPS systems etc, is essential for • a smooth and consistent access to services.

The following list is a set of options that could be used in network security:Firewalls at all public-private network transit points• Version controlled and centrally deployed firewall rule sets• External resources placed in dual firewall, dmz protected networks• All network hosts lock down unneeded network ports and turn off unneeded services• All network hosts include centrally managed anti-virus software and utilise central security updates• Secure central authentication such as radius, windows/kerberos/active directory•


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Centrally managed user management with password policy (must change every three months and must be a • ‘secure password’)Proactive network scanning for new hosts, out of date systems• Network monitoring for suspicious behaviour• Incident response mechanisms (policies, manual, automated and so on).•

7.4 Uses of InternetIn spite of all the security issues discussed above, networks, especially internet, are one of the most essential components of routine life of individuals. This is not to exaggerate, but to underline the significance of internet and its services in today’s world.

Some of the important applications of internet are:Access to remote information• World wide web• Person-to-person communication with electronic mail, videoconference, and so on• Interactive entertainment like video-on-demand, games and so on• Online shopping, booking, trading, social networking and so on.•

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SummaryThe use of internet began in 1969 at the U.S. Department of Defence’s Advanced Research Project Agency • (ARPA) to provide immediate communication within the department in case of war.The key components of internet architecture are the protocol, IP address, domain name service, packet switching, • internet routers, and backbone.Securing the modern business network and IT infrastructure demands an end-to-end approach for firms in grasp of • possible security threats and should be associated with protective measures. Threats can come from both internal and external sources. They may be human based, automated or even non intentional natural phenomenon.A computer virus is a self-replicating computer program that behaves like a biological virus. There are different • types of viruses like Trojan horses, worms, and email viruses.Securing all equipment, including physical infrastructure equipment is essential. Antivirus software, firewalls, • etc. can be used as measures for secure network usage.Internet has enhanced and eased access to remote information and communication, with some of its services • like the World Wide Web.

ReferencesOppliger, R., 2001. • Internet and Intranet security, 2nd ed. Artech House.Kizza, M. J., 2005.• Computer Network Security, Springer.Dr. James H. Yu & Mr. Tom K. Le, • Internet and Network Security [Pdf] Available at: <http://www.nait.org/jit/Articles/yu101800.pdf> [Accessed 28 May 2013].Network Security: History, Importance, and Future• [Pdf] Available at: <http://web.mit.edu/~bdaya/www/Network%20Security.pdf> [Accessed 28 May 2013].Prof. Ghosh, S., • Lecture - 38 Security [Video online] Available at: <http://www.youtube.com/watch?v=3JblSrRT8XE> [Accessed 28 May 2013].Prof. Sengupta, I., 2008. • Lecture - 31 Intranet, Extranet, Firewall [Video online] Available at: <http://www.youtube.com/watch?v=vS0khTah3zU> [Accessed 28 May 2013]

Recommended Reading McNab, C., 2009. • Network Security Assessment: Know Your Network, 2nd ed. O'Reilly Media, Inc.Joshi, J., 2008. • Network Security: Know It All: Know It All, Morgan Kaufmann.Maximum Security• , 4th ed. Sams Publishing


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Self AssessmentSince all smaller networks are linked together into one giant network called the internet, it is also known as 1. ____________.

internet networksa. network of networksb. large networkc. linked networkd.

Internet began under which U.S. department?2. National Defence Agencya. National Science Foundationb. Advanced Research Project Agencyc. Advanced Defence Project.d.

Two networks which may be very different in internal hardware, software, and technical design are connected 3. with the help of?

TCP/IP protocola. Cablesb. Connectorsc. Communicatorsd.

An Internet Protocol (IP) address is used to ____________across the internet. 4. packet switchinga. route switchingb. address locationc. route packetsd.

The key idea of packet switching is the division of each communication into individual ____________.5. large packetsa. small packetsb. equal-sized packetsc. uneven packetsd.

Which of the following information is not recorded by the packet header?6. Destinationa. Dateb. Lengthc. Sequenced.

Router uses ____________ to send the packet across the internet to the destination computer.7. route switchinga. routing messageb. packet switchingc. routing algorithmd.

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The ____________ has multiple fibre optic cables.8. trunk linea. hardwareb. connectorsc. switchesd.

Trojan horse is a type of:9. Computer soft warea. Computer virusb. Computer hard warec. Security systemd.

Firewalls are basically application specific____________.10. systemsa. hurdlesb. routersc. protocolsd.


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Chapter VIII

World Wide Web

Aim


explain the workflow of WWW•

elucidate the ways to use web effectively•

explicate advanced application of WWW•

Objectives


explain the history of WWW•

enlist the importance of web page, URL, HTML and HTTP•

explain the role of web browsers, search engines•

Learning outcome


identify and list key elements important for functioning of web•

understand the essential factors of WWW•

descrine the uses of search engines and directories•

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8.1 IntroductionIn 1989, Tim Berners-Lee, a physicist at CERN (European Organisation for Nuclear Research), wrote a proposal for information management showing how information could be transferred easily over the internet by using hypertext, the now familiar point-and-click system of navigating through information. He was later joined by Robert Cailliau in the project.

The idea was to connect hypertext with the internet and personal computers, thereby having a single information network to help CERN physicists share all the computer-stored information at the laboratory. Hypertext would enable users to browse easily between texts on web pages using links. The first examples were developed on NeXT computers.

Berners-Lee created a browser-editor with the goal of developing a tool to make the web a creative space to share and edit information and build a common hypertext. They thought of various names like: “The Mine of Information”, “The Information Mesh” for the browser. They settled on a name in May 1990 and it was the World Wide Web (WWW), now simply referred as “web.”

People often use the terms internet and WWW interchangeably, which is incorrect. The internet and the web work together, but they are not the same thing. The Internet provides the underlying structure, and the web utilises that structure to offer content, documents, multimedia, etc.

8.2 Functioning of the WWWSimply put, it is the documents referring to each other by links. For its likeness to a spider’s construction, this • world is called the web. This is known as the hypertext paradigm. The reader sees a document on the screen with sensitive parts of text • representing the links. A link is followed by mere pointing and clicking.Hypertext alone is not practical when dealing with large sets of structured information such as what is contained • in data bases: adding a search to the hypertext model gives W3 its full power. Indexes are special documents which, rather than being read, may be searched. To search an index, a reader • gives keywords (or other search criteria). The result of a search is another document containing links to the documents found.

Figure below will help to understand the explanation more clearly.

document

anchorlink

A

B

C

XY

Z

Phone Book

Search

You can link to the resultof a search.

IndexServer

Bloggs

Bloggs,Joe:4657

Synthesizedhypertext

telephoneindex

Fig. 8.1 Basic hypertext enhanced by searches(Source: http://www.freehep.org/chep92www.pdf)


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We will now discuss the key elements of the web, and understand its functioning.

8.2.1 Web Page

From the user's point of view, the page is the basic unit of the web. Web pages are written in the HTML language • and sent to web browsers via web server using the HTTP protocol. A web page has a similar page format as of a book or magazine, with text and graphics displayed in a layout, • and it is displayed in a normal computer application window. Collection of related web pages, images, videos or other digital assets that are addressed relative to a common • Uniform Resource Locator (URL) is called as a website. A web site is hosted on at least one web server.

8.2.2 URL

Web addresses are recorded in a URL, a logical address of a web page that can always be used to dynamically • retrieve the current physical copy over the internet. The key advantage of URL is its universality, since the address is same no matter where in the world it is • used.

8.2.3 Web Server Every web site is managed by a web server. The web server handles all the network communication with individual user browsers. The server accepts HTTP requests for web pages, and sends the requested pages to browsers over the internet. Different web servers have different scalability, robustness, security, transportability, and related features. A web server may be dedicated for one domain name, or maintain web sites for several domains.

8.2.4 HTTPThe Hypertext Transfer Protocol (HTTP) is used by web servers to communicate web pages to web browsers. HTTP is used when a browser connects to a web server, requests a web page from the server, and downloads the page. It is the common standard that enables any browser to connect to any server, anywhere in the world. The HTTP protocol is designed to permit intermediate network elements to improve or enable communications between clients and servers.

8.2.5 HTMLHyper Text Mark up Language (HTML) is the publishing language of the World Wide Web. It is a simple and powerful language used to describe web pages, and is still used as the main interface language to the web. Each command consists of an opening tag in angle brackets, like <tag>, and a closing tag with an added slash, like </tag>.

To understand how it exactly helps, we can analyze it step by step.We can “move” around the web using “hypertext” — by clicking on special text called hyperlinks which take • us to the next page. “Hyper” just means it is not linear — i.e. one can go to any place on the internet whenever they want by clicking • on links — there is no set order to do things in.Mark up is what HTML tags do to the text inside them. They mark it as a certain type of text (italicized text, • for example).HTML is a language and has code-words and syntax like any other language.•

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8.3 Using the WWWUsing the web requires some kind of interface for convenient access to the resources made available. Web browser is such an interface. Optimum browsing results can be achieved by efficient search methods.

8.3.1 Web BrowserA web browser or internet browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to related resources. Although browsers are primarily intended to access the World Wide Web, they can also be used to access information provided by web servers in private networks or files in file systems. Some browsers can also be used to save information resources to file systems. Examples of popular browsers used are, Internet Explorer, Mozilla Firefox and so on.

8.3.2 Searching for Information There are two broad ways to adapt for effective search results. Using a directory site or a search engine helps in simplifying and filtering search results and save extra time and efforts.

Directory sitesDirectory sites place each web site in their database in one or more predefined subject categories following • review by a moderator. A web site is included in a directory site's database only after it has been judged for its usefulness, information, • or otherwise worthwhile. Typical reasons a site might not be included in the database are because it isn't unique enough, it isn't guaranteed • to remain around for long, or it doesn't meet some other guideline or criteria. Examples of some popular directories are Google directory, Yahoo directory, Internet Public Library and so • on.

Search enginesSimply put, a search engine enables to search the internet for information of interest. Search engines work by • storing information about many web pages, which they retrieve from the HTML itself. These pages are retrieved by web crawler (sometimes also known as a spider) — an automated web browser which follows every link on the site.The contents of each page are then analyzed to determine how it should be indexed (for example, words are • extracted from the titles, headings, or special fields called Meta tags).Data about web pages are stored in an index database for use in later queries. A query can be a single word. The • purpose of an index is to allow information to be found as quickly as possible. Some search engines, such as Google, store all or part of the source page (referred to as a cache) as well as information about the web pages, whereas others, such as AltaVista, store every word of every page they find.When a user enters a query into a search engine (typically by using key words), the engine examines its index and • provides a listing of best-matching web pages according to its criteria, usually with a short summary containing the document's title and sometimes parts of the text. The index is built from the information stored with the data and the method by which the information is indexed.

8.3.3 Search TechniquesMost search engines support the use of the Boolean operators AND, OR and NOT to further specify the search query. Boolean operators are for literal searches that allow the user to refine and extend the terms of the search. The engine looks for the words or phrases exactly as entered. Some search engines provide an advanced feature called proximity search which allows users to define the distance between keywords. There is also concept-based searching where the research involves using statistical analysis on pages containing the words or phrases searched for. As well, natural language queries allow the user to type a question in the same form one would ask it to a human. Example of such site would be Ask.com.


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8.4 Advanced Application: Emergence of Web 2.0A revolutionary change that swept the web and allowed users to interact with the data available is the emergence of Web 2.0. The term Web 2.0 is commonly associated with web applications that facilitate interactive information sharing, interoperability, user-cantered design, and collaboration on the World Wide Web.

A Web 2.0 site gives its users the free choice to interact or collaborate with each other in a social media dialogue as creators of user-generated content in a virtual community, in contrast to websites where users are limited to the passive viewing of content that was created for them.

Examples of Web 2.0 include social-networking sites, blogs, wikis, video-sharing sites, hosted services, web applications, mashups and folksonomies.

BlogsIt is short form for “Web log” - an online diary that keeps a running chronology of entries. Readers can comment on posts and can connect to other blogs through blog rolls or trackbacks.

AdvantagesShare ideas easily• Advertise • Obtain feedback• Reverse chronology• Mobilise a community • Comment threads• Persistence• Search ability• Tags• Trackbacks•

WikisIt is a web site that anyone can edit directly within the browser. They are huge information resources on wide variety of topics.

AdvantagesCollaborate on common tasks • To create a common knowledge base • A complete revision history is maintained with the ability to roll back changes and revert to earlier versions • All changes are attributed• Automatic notification of updates• Search ability• Tags• Monitoring•

Electronic Social NetworkOnline community that allows users to establish a personal profile, link to other profiles (i.e., friends), share content, and communicate with members via messaging, posts. Examples of social networking sites are Facebook, LinkedIn, Orkut and so on.

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AdvantagesDiscover and reinforce affiliations• Identify experts• Message individuals or groups• Virtually share media• Detailed personal profiles using multimedia• Affiliations with groups and individuals• Messaging and public discussions• Media sharing• “Feeds” of recent activity among members•

Micro BloggingIt is a short, asynchronous messaging system. Here, users post messages in general or to specific followers which are displayed on the user’s page. Popular example of micro blogging site is Twitter.

AdvantagesDistribute time-sensitive information• Share opinions• Virtually spread ideas• Run contests and promotions• Solicit feedback• Provide customer support• Track commentary on firms/products/issues• Organise protests•

RSSIt is an acronym that stands for both “really simple syndication” and “rich site summary”. It enables busy users to scan the headlines of newly available content and click on an item’s title to view items of interest, thus sparing them from having to continually visit sites to find out what’s new.

Web 3.0The difference between web 2.0 and web 3.0 is not very evident and it is considered to be an extension of web 2.0.

The web (web 1.0) before web 2.0 was more about finding and reading available data. Web 2.0 is more interactive, with users participating in information generation and exchange. Web 3.0 is more about meaning of data, the semantic web, personalisation and intelligent search.

By the end of this chapter, we can say that the World Wide Web and its constant up gradation and evolution provide us with the greatest way of creating, accessing and interacting with information around the world.


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SummaryThe Internet and the Web work together, but they are not the same thing. Internet provides the underlying • structure, and the web utilises that structure to offer content, documents, multimedia and so on.Web works by the documents referring to each other by links. For its likeness to a spider’s construction, this • world is called the web. Web page is the basic unit of the web. It is written using HTML and sent to the web server using the HTTP protocol.The Hypertext Transfer Protocol (HTTP) is used by web servers to communicate web pages to web browsers, • while Hyper Text Mark up Language (HTML) is the publishing language of the World Wide Web. It is a simple and powerful language used to create web pages.Using the web requires some kind of interface for convenient access to the resources. Web browser is such an • interface. A web browser or internet browser is a software application for retrieving, presenting, and traversing information resources on the WWW.There are two broad ways to adapt for effective search results. Directory sites place each web site in their • database in one or more predefined subject categories following review by a moderator. A search engine enables to search the internet for information of interest. Search engines work by storing information about many web pages, which they retrieve from the HTML itself.Web 2.0 is very interactive, with users participating in information generation and exchange. Web 3.0 is more • about meaning of data, the semantic web, personalisation and intelligent search. We can say that the World Wide Web and its constant up gradation and evolution provide us with the greatest way of creating, accessing and interacting with information.

ReferencesMorville, P. & Rosenfeld, L., 2008.• Information Architecture for the World Wide Web: Designing Large-Scale Web Sites, 3rd ed. O'Reilly Media, Inc.Burnett, R. & Marshall, D. P., 2003. • Web Theory: An Introduction, Routledge.World-Wide Web = WWW• [Pdf] Available at: <http://www.vub.ac.be/BIBLIO/nieuwenhuysen/courses/chapters/www.pdf> [Accessed 28 May 2013].AN INTRODUCTION TO THE WORLD WIDE WEB• [Pdf] Available at: <http://www.eolss.net/Sample-Chapters/C15/E6-200-03.pdf> [Accessed 28 May 2013].Prof. Sengupta, I., 2008. • Lecture -11 World Wide Web Part-I [Video online] Available at: <http://www.youtube.com/watch?v=-2hpoIjNSb4> [Accessed 28 May 2013].History of the Internet• [Video online] Available at: <http://www.youtube.com/watch?v=-2hpoIjNSb4> [Accessed 28 May 2013]

Recommended ReadingYeager, N., 1996. • Web Server Technology: The Advanced Guide for World Wide Web Information Providers, Morgan Kaufmann.Sebesta, 2008. • Programming With World Wide Web, 4/E, Pearson Education India.Hawisher, E. G. & Selfe, L. C., 2000. • Global Literacies and the World-Wide Web, Routledge

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Self AssessmentThe ____________and the Web work together.1.

intraneta. internetb. LANc. WANd.

Documents referring to each other by hyperlinks is known as:2. Hyper text paradigma. Hyperlink networkb. Networkc. Internetd.

What gives the web its full power?3. Connectivitya. Communicationb. Searchingc. Linkingd.

What does the user normally use to search an index?4. Linksa. Internetb. WWW c. Keywordsd.

A web site is hosted on ____________.5. WWWa. web serverb. internetc. WANd.

A logical address of a web page that can always be used to dynamically retrieve the current physical copy over 6. the Internet, is known as:

HTMLa. HTTPb. URLc. Web sited.

The web server handles all of the____________with individual user browsers.7. network communicationsa. communicationsb. web sitesc. web pagesd.


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____________ place each web site in their database in one or more predefined subject categories following 8. review by a human being.

Search enginesa. Directory sitesb. Keywordsc. Web serversd.

To specify the search query, most search engines support the use of AND, OR and NOT, which are known as 9. ____________.

Proximity searcha. Keywordsb. Boolean operatorsc. Concept searchd.

Blogs, wikis, video-sharing sites, hosted services, web applications, mashups and folksonomies are all examples 10. of ____________

Web sitesa. Web gamesb. Internet sitesc. Web 2.0 servicesd.

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Application I

Computers in Airline Reservations

A computer reservation system or CRS is a computerised system that is used for reservation purpose in airlines, railways and buses. This computerised system is used to store and retrieve information; and conduct transactions related to the transport. This was originally designed and operated by airlines.

Thus, computer technology has made the airline reservation system quite effective and less time consuming. It is observed that reservation system in airlines is almost error free and provide various facilities.

A typical airline system includes following information:Flight details: This includes the information like starting destination and end destination, along with the stops • in between, and the number of seats booked/available.Customer description: This section includes customer’s name, code, address, phone number, and seat number • allotted. This information is useful for keeping the records of customers for any emergency.Reservation description: This includes information like customer’s code number, flight number, date of booking, • and date of travelling.

The computerised reservation system has made the reservation procedure of airlines easier and less time-consuming. The airlines are able to meet their ticket sales target and maintain their tickets selling ratio. It also reduces confusion from the point of view of customers. Thus, computer technology has transformed the reservation system in the airline industry and relieved the customers from a tedious and prolonged reservation procedure.

QuestionsHow is the computer technology useful in the airline reservation?1. AnswerThe computerised reservation system or CRS is used in the airline reservation. This form of computer technology is used to store and retrieve information; and conduct transactions related to the transport.

What are the advantages of computerised reservation system for the airline industry?2. AnswerThe advantages of the computerised reservation system for the airline industry are as follows:

The computerised reservation system has made the airline reservation system quit effective and less time-• consuming.It is observed that reservation system in airlines is almost error free and provide various facilities. • Due to CSR, the airlines are able to meet their ticket sales target and maintain their tickets selling ratio. • It has also reduced confusion from the point of view of customers and have made travelling a lot more • easier.

What information is available on a typical airline system?3. AnswerA typical Airline System includes following information:

Flight details: It includes the information like starting destination and end destination, along with the stops • in between, and the number of seats booked/available.Customer description: This section includes customer’s name, code, address, phone number, and seat number • allotted. This information is useful for keeping the records of customers for any emergency.Reservation description: It includes information like customer’s code number, flight number, date of booking, • and date of travelling.


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How is the computerised reservation system beneficial from the point of view of customers?4. AnswerThe computerised reservation system has made the reservation procedure of airlines easier and less time-consuming. It has reduced the confusion from the point of view of customers. Thus, it has relieved the customers from a tedious and prolonged reservation procedure. It has eased the payment procedure and has made travelling a simple procedure.

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Application II

Computers in Education and Training

Computers have transformed the traditional form of teaching and training. The advent of computers has made a remarkable change in children’s life. It has enhanced their knowledge and has given a wider scope to search information they need.

Computers serve as a tool in education and training field. It can be used as different type of tool for different purposes:Communications Tool

e-mail• cell phones•

Publishing Toolpresentation software• drawing software• internet publication• reports•

Research Toolinternet access• library card catalogue• periodical listing• reference software•

Teaching Tooldrill and practice• interactive instruction• modelling• programming• tutorials•

Advantages of Computers in EducationComputers help the school children to be in control of their experience, set their own pace, and to select the • level of challenge which they feel comfortable. To extract the information, the children make use of all their senses and there is no spoon feeding from their • mentors. Thus, children gain information in less time. Computers fascinate the kids and draw their attention, making them more attentive and help in concentrating.• Computers also help in enhancing creative skills like painting, making up stories, solving puzzles and so • forth.Good educational software can make the learning to be a cheerful experience and full of activities for the children. • This reduces the work of teachers and gives them better opportunities in developing the teaching skills.Good educational software enables children to develop and practice many skills like letters, numbers, shapes, • colours, rhythm and the likes.


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Thus, computers have made a remarkable change in education field by implementing good educational soft wares. This makes teaching easier for the teachers and facilitates quick learning for children.

QuestionsExplain the role of computers as a teaching tool?1. How has the training and education transformed after the introduction of computers?2. What are the advantages of computers in educating school children?3. How can good educational software reduce the work of teachers?4.

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Application III

Computers in Banking

Today’s computer technology has transformed the traditional banking system with the online banking concept. The online banking is one of the forms that have helped the banks and the customers in various ways. The online banking is less time –consuming, and has reduced the work of the people. Thus, it has reduced the work of the banks and made the transaction of money easier.

Origin of Online BankingThe introduction of internet and the popularity of personal computers, both gave an opportunity and challenge for the banking industry. The concept of online banking slowly began to spread in most of the banks as it reduced a lot of burden of work of both the bank and the customer. After the online banking concept was established, many banks faced problems in initial stages of setting the online system. However, slowly, online banking became popular and was powerful “value added tool” to attract and retain customers. It also helped to eliminate the lengthy banking transaction procedures, costly paper handling and teller interactions, and made banks to stand firm in competitive banking environment. Since people are now aware of the online banking concept and are familiar in handling it, banks have developed stable online banking and offer variety of services online.

The computer technology has helped banking sector to set up different types of banking facilities like:PC banking• home banking• electronic banking• internet banking.•

AdvantagesThe advantages of online banking are as follows:

Convenience: Online banking facilities are available 24 hours, seven days a week, unlike the normal banks. Thus, • online banking is quite convenient. It can be accessed even if a customer is in other country or other state. Transaction speed: Online banking sites execute the transactions quicker than the ATM processing.• Efficiency: Online banking is secured and one can easily access and manage the bank accounts, which include • IRA’s, CD’s and so on.Effectiveness: Most of the online banking sites offer different tools like account aggregation, stock quotes, • rate alerts and portfolio managing programs, transfers and so on that are beneficial in managing all assets effectively.

DisadvantagesThere are also some disadvantages of online banking. These are as follows:

Longer Start-up phase: In order to register with the online banking, the bank should provide ID and this may • take time. The bank sites may take longer time while trying to register for the first time. Learning curve: Banking sites may be confusing to some people and they may end up processing incorrect • transactions. Bank site changes: Most of the banks may incorporate changes in the bank sites or upgrade the sites and this • may create problems for the customers.Lack of Trust: Most of the people find it difficult to trust the bank sites. Old people may find it difficult to trust • the security of the transactions online and prefer the banking transaction to be carried out personally. Also, people fear the incidents of online account hacking.


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Most of the people find online banking as a flexible mode of money transaction, and they can view their accounts at a click. Thus, computer technologies have changed the life of customers and also have transformed the way banking sector used to work.

QuestionsHow has computer technology transformed the traditional banking concept?1. What are the advantages and disadvantages of online banking?2. Which are the different ways in which computer technology is used in banking sector?3. How is online banking convenient than the traditional form of banking?4.

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Kesidis, G., 2007. • An Introduction to Communication Network Analysis, John Wiley & Sons.Kifer, M. & Smolka, S., 2007. • Introduction to Operating System Design and Implementation: The OSP 2 Approach, Springer.Kizza, M. J., 2005. • Computer Network Security, Springer.Kumar, V. & Kumar, D., • LESSON 1 INTRODUCTION TO DATA PROCESSING [Pdf] Available at: <http://www.ddegjust.ac.in/studymaterial/pgdca/ms-09.pdf> [Accessed 24 May 2013].Learn Introduction to O S from the Fundamentals of Operating Systems• [Video online] Available at: <http://www.youtube.com/watch?v=cP-OPjwag4E> [Accessed 22 May 2013]Lecture - 3 Introduction To System : Hardware• [Video online] Available at: <http://www.youtube.com/watch?v=FOyuMclwymw> [Accessed 28 May 2013].Micallef, A. B., 1971. • An introduction to data processing, Cummings Pub. Co.Morville, P. & Rosenfeld, L., 2008. • Information Architecture for the World Wide Web: Designing Large-Scale Web Sites, 3rd ed. O’Reilly Media, Inc.Murphy, M., 2011. • Introduction to Operating Systems [Video online] Available at: <http://www.youtube.com/watch?v=MzVGL44eq9w> [Accessed 22 May 2013].Network Security: History, Importance, and Future• [Pdf] Available at: <http://web.mit.edu/~bdaya/www/Network%20Security.pdf> [Accessed 28 May 2013].Oppliger, R., 2001. • Internet and Intranet security, 2nd ed. Artech House.Prof. Ghosh, S., • Lecture - 38 Security [Video online] Available at: <http://www.youtube.com/watch?v=3JblSrRT8XE> [Accessed 28 May 2013].Prof. Ghosh, S., • Lecture -1 Emergence of Networks & Reference Models [Video online] Available at: <http://www.youtube.com/watch?v=3DZLItfbqtQ&list=PLD6F332057F76C54C> [Accessed 28 May 2013].Prof. Kumar, A., 208. • Lecture -1 Introduction to Computer Architecture [Video online] Available at: <http://www.youtube.com/watch?v=4TzMyXmzL8M> [Accessed 28 May 2013].Prof. Sengupta, I., 2008. • Lecture - 31 Intranet, Extranet, Firewall [Video online] Available at: <http://www.youtube.com/watch?v=vS0khTah3zU> [Accessed 28 May 2013].Prof. Sengupta, I., 2008. • Lecture -11 World Wide Web Part-I [Video online] Available at: <http://www.youtube.com/watch?v=-2hpoIjNSb4> [Accessed 28 May 2013].Protocols and Computer Networks part 1• [Video online] Available at: <http://www.youtube.com/watch?v=Q3SsVO0eSOU> [Accessed 28 May 2013].Saskatchewan Learning, 2002. • Information Processing 10, 20, 30 Curriculum Guidelines [Pdf] Available at: <http://www.edcentre.ca/resources/info10/currmain.pdf> [Accessed 28 May 2013].Shelly, B. G. & Vermaat, E. M., 2009. • Discovering Computers: Living in a Digital World : Fundamentals, 6th ed. Cengage Learning.Shelly, B. G., Freund, M. S. & Vermaat, M., 2010. • Introduction to Computers, 8th ed. Cengage Learning.Shim, K. J., 2002. • Information Systems and Technology for the Noninformation Systems Executive: An Integrated Resource Management Guide for the 21st Century, CRC Press.Stallings, W., 2007. • Data And Computer Communications, 8/E, 8th ed. Pearson Education India.Thierauf, J. B. & Niehaus, F. J., 1980. • An introduction to data processing for business, Wiley.World-Wide Web = WWW• [Pdf] Available at: <http://www.vub.ac.be/BIBLIO/nieuwenhuysen/courses/chapters/www.pdf> [Accessed 28 May 2013].

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Self Assessment Answers

Chapter Ib1. a2. c3. a4. d5. c6. b7. c8. d9. b10.

Chapter IIb1. a2. c3. d4. b5. c6. d7. a8. c9. b10.

Chapter IIIb1. a2. c3. d4. b5. a6. d7. a8. b9. c10.

Chapter IVc1. b2. a3. d4. a5. b6. c7. d8. b9. a10.

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Chapter Vb1. a2. c3. a4. c5. d6. b7. d8. a9. c10.

Chapter VIa1. b2. d3. b4. c5. b6. c7. d8. c9. 10. a

Chapter VIIb1. c2. a3. d4. c5. b1. d2. a3. b4. c5.

Chapter VIIIb1. a2. c3. d4. b5. c6. a7. b8. c9. d10.