comps ys book

8/13/2019 Comps Ys Book

1/63

1

CONTENTS

UNIT - 1 COMPUTER CONCEPTS1.0Introduction

1.1 Objectives

1.2 Need for Computer Literacy

1.3 Computer Capabilities

1.4 Computer Concepts

1.5 A Typical PC Characteristics

1.6 Question/ Answer Key

UNIT 2 COMPUTER SYSTEM ORGANIZATION

2.0 Introduction

2.1 The System Concept

2.2 Organization of Computer System

2.2.1 Input Devices

2.2.2 Central Processing Unit (CPU)

2.2.3 Output Devices

2.3 Computer Limitation

2.4 Classification of Computers


UNIT 3 SOFTWARE

3.0 Introduction

3.1 Software.

3.1.1 System Software

3.1.2 Application Software

3.2 Machine Language

3.3 Assembly Language

3.4 High Level Language



2/63

2

Chapter 1

COURSE INTRODUCTIONComputers are used in many application, like banking, military, medical instruments.

In this course we are going to discuss the fundamental concept of computers, its working,

how computer are useful for a society and its capability. How computers are classified,

what is the relationship between software and hardware and what is the use of storage

device and their capabilities are discussed.

Peripheral devices are responsible for carrying out input and output operations. The

input devices include keyboard, mouse, light pen etc.. The output devices are printers,

plotters and the monitors to name a few. Computer is an information process device,

Hence devices for storing information are needed. Main memory holds programs and

data. Main memory is volatile and limited in size. Secondary storage devices are non-

volatile and have sizes which are orders of magnitude more than the size of the main

memory. Example of secondary storage are hard disk, floppy disk, CD ROM computers

store information in the digital form. In order to make a computer communicate with the

analog world, a device called MODEM( Modulator Demodulator ) is used. Modem

converts the digital information to analog information for messages going out of acomputer and vice-versa for incoming messages. Different computers might be

equipped with different resources. For example a computer might have a printer attached

and another. Computer might have useful programs. Sharing of resource will logically

see that every computer will be able to use all the resources ( whether available locally or

not). Resource sharing becomes possible of the computer are connected together. LAN (

Local Area Network ) provide for resource sharing.

In a network of computers programs are distributed on the different computers. A

computer may have a program providing a certain service ( say printing ) running on it.

It is useful to make the service available for requests coming from else where.

Client/Server technology provides for service to be extended to request client request

origination from any point of the network.

Multimedia technology add multimedia capabilities ( audio, video) to a computer.

A multimedia kit normally has a sound card, CD-ROM or DVD Drive and speakers.


3/63

3

UNIT - 1 COMPUTER CONCEPTS

STRUCTURE

1.0Introduction1.1 Objectives1.2 Need for Computer Literacy

1.3 Computer Capabilities

1.4 Computer Concepts

1.5 A Typical PC Characteristics1.6 Question/ Answer Key

1.0 INTRODUCTION

No other technology has made such a rapid growth and change in science and

technology in a short duration of time as the computer technology. Computers have a

become a part and parcel of every human beings life. One can imagine the power and

position of computers by looking into the statements " By the year 2099, there will be no

clear distinction between humans and machines, we will have merged". Within the next

20 years, computers will be powerful like our human brain.

Though computers by themselves have no intelligence and do not have the ability to

learn, they have created situations that make us feel as if computers are better than human

beings. In some ways, computers are fast, store large volumes of data and are more

efficient than human beings. Computers are largely self-directing i.e. they have the

ability to follow the set of instructions given to them ( of course, by human

beings!)without human interaction.

With limited intelligence, limited language capability (understands only

programming languages) computers continue to dominate in the field of science and

technology.

The computers have emerged as a result of countless ideas inventions and

developments made by different people throughout this century.

1.1 OBJECTIVES

After studying this unit you should be able understand computer capabilities,

functional blocks of a computer the difference between data and information, speed and

accuracy capabilities. How data is manipulated.


4/63

4

1.2 NEED FOR COMPUTER LITERACY

A few decades ago, a few computers in existence were very huge and expensive,

they were usually used for scientific purposes and thus had little impact on the lives of

common people; only a few people had the knowledge of computer capabilities and

limitations.

But over the period the scenario has changed. Millions of computers ranging from

small micro-sized units to super-computers are found in offices, factories, schools,

homes, hospitals, banks, retail stores and almost every where.

Let us take a few examples and look at the use of computers

a) Travel arrangements for a trip:

An efficient computer controlled airline reservations system keeps track of

available seats and quickly records the reservation.

b) You went to a hospital for physical checkup:

If the exam is for insurance purposes, your medical history and the doctors

finding will be forwarded to the insurance company where they are stored in a

large computer data bank.

c) Visit to a supermarket:

When you go to a supermarket you can find several computers, which read the

codes (like bar code) on the products and prepares the cash bills within a few

minutes. There is no need for the customer to wait for a long time to get his

bill.

By looking at the typical sample examples listed above, the presence of computers in

your daily life cannot be ignored or under estimated.

Computers can have both good and bad effects on the individuals.

Computer applications will expand greatly in the years to come. There will be vast

potential for widespread benefits as well as undesirable side effects. Educated citizensshould not rely solely on computer specialists to prevent the possible dangers and bring

about the positive potential. Rather, citizens should learn about computers so that they

can reap the benefits and they can insist the designers of ill-conceived computer systems

to assume the responsibility for effects these systems have on people.


5/63

5

The following are the areas of knowledge required for computer literacy:

1. Computers themselves: You should understand the organization,

capabilities and limitations of the various machines or hardware that make

up a modern computer system.

2. What computers do: You should be familiar with some of the most

common applications of computers in today's society.

3. How computers are put to work: You need to know the analysis, design

and program preparation procedures that must be carried out in order to

produce software. Basic knowledge of hardware is also very essential.

4. The social impact of computers at work: Finally you should know how

individuals and organizations may be affected by present and future

computer applications.

1.3 COMPUTER CAPABILITIES

Most people are aware that a computer is a machine that can perform arithmetic

operations, but it is much more than just an arithmetic number crunching device. It is

also a machine that can choose, copy, move compare and perform various non-arithmetic

operations on many alphabetic, numeric and other symbols that humans use to represent

things. The computer manipulates these symbols in the desired way through a sequence

of instructions, called a program.

A program is a detailed set of human instructions that directs the computer to

function in a specific way to produce a desired result. Electrical or electromechanical

components are known as hardware.

a. Speed and accu racy capabil i t ies:

A computer works one step at a time. It can add, subtract, compare digits and,

letters, move and copy numbers and letters. There's nothing profound in these

operations. What's significant is the computer speed. This speed is measured asmilliseconds, microseconds, nanoseconds and pico seconds (Recent study says computer

speed is being doubled every six months).

The speed required for computers to execute a basic operation like addition varies

from a few microseconds for the smallest machines to 80 nano seconds or less for the

larger ones.


6/63

6

Thus, the slowest computers can perform hundreds of thousands of additions in a

second while the largest systems can compute several million additions in the same

period.

In addition to being very fast, computers are also very accurate. It is estimated that

you or I would make one error in every 500 to 1,000 operations with a calculator. But the

circuits in a computer require no human interaction between processing operations and

have no mechanical parts to wear out and malfunction. Thus these circuits can perform

hundreds of thousands (or millions) or operations every second and can run errorless for

hours and days together at a time.

Beyond this, computers also have built-in self-checking capabilities that permit them

to monitor the accuracy of their internal operations.

If the input data are correct and relevant, and if the program of processing the

instructions is reliable, then the computer can generally be expected to produce accurate

output. The phrase " Garbage in, Garbage-out" or GIGO is used often by people who

work with computers to illustrate the importance of input data and correct instruction.

b. Data manipulat ing c apabi l ity :

The first computers were built to manipulate numbers in order to solve arithmetic

problems. Along with numbers we also use alphabets and different symbols in our daily

life. Luckily, early computer experts made the important discovery that a machine that

can accept, store and process numbers can also manipulate non-numeric symbols.

Manipulating these familiar symbols is possible if an identifying code number is assigned

to the symbol to be stored and processed. Thus, the letter A can be represented by a

code, as can the letter B, the addition symbol and so on. Of course, one must give the

computer instructions for it to manipulate the coded and stored symbols in a desired way.

c. Data - versu s - inform ation:

The word " data" is the plural of datum, which means fact. Data then, are facts or

raw material of information. Data are represented by symbols.

Information is data arranged in ordered or useful form. That is information is

relevant knowledge produced as output of data processing operations and acquired by

people to enhance understanding and to achieve specific goals.

The following schematic representation shows you the processing of raw data to

provide information:


7/63

7

Data Raw data Data Information End user

decisionsCollection input processing output and

actions

d. Data Process ing activi t ies:

Data processing consists of gathering the raw data input, evaluating and bringing

order to it and placing it in proper perspective so that useful information is produced. All

data processing, whether done by hand or computer system consists or three basic

activities: capturing the input data, manipulating the data and managing the output

results.

i) Capturing the input data:

Data must be originated in some form and verified for accuracy prior to further

processing. They may initially be recorded on paper source documents and then

converted into a machine - usable form processing or they may be captured directly in

paperless machine-readable form.

ii) Manipulating the data:

One or more of the following operation may have to be performed on the data that is

collected.1. Classifying:Organizing items with like characteristics into groups or classes is

called classifying. Data taken from a materiel stores sales bill for example, may

be classified by product sold, Sales department sales person, or any other

classification useful for store management. Classifying is usually accomplished

by assigning pre-determined abbreviation codes to the items being arranged. The

three types of codes used are numeric, alphabetic and alphanumeric.

2. Sorting: Usually its easier to work with data if they are arranged in a logical

sequence. For example: include first to last, biggest to smallest oldest to newest.

Arranging classified data in such a sequence is called sorting.

3. Calculating: Arithmetic manipulations of the data is called calculating. For

example: In calculating a sales person's pay, the hours worked multiplied by the

hourly wage rate gives the total earnings. Payroll deductions such as taxes are


8/63

8

then calculated and subtracted from total earnings to arrive at the sales person's

take-home pay.

4. Summarizing: Reducing masses of data to a more concise and usable form is

called summarizing.

Example: the general manager of a retail store is interested only in a summary of

the total sales of each department. A summary report would give only total sales

information. Department managers may want more detailed information such as

the total sales of each department broken down into sales by product type and by

sales person.

e. Managing the outp ut resul ts:

Once the data have been captured and manipulated, one or more operations may beneeded.

i) Storing and retrieving: Retaining data for future reference in storing,

storage media such as paper ( in sheet, punched card or punched tape

form), microfilm, or magnatic disks and tapes are generally used.

Recovering stored data and / or information is the retrieving activity. One

slow approach is for people to search file cabinets. A much faster method

is to use electronic enquiry devices that are connected directly to a

computer and mass storage unit containing the data.

ii) Communicating and reproducing: Transferring data from one location

or operation to another for use or for further processing is data

communication a process that continues until information in a usable

form, reaches the final user. Some times of course, its necessary to copy

or duplicate data. This reproduction activity may be done by hand or by

machine.

1.4 COMPUTER CONCEPTS

There's nothing new about the data processing steps just stated above. They have

been performed down through the ages, first by hand, then by machine assisted manual

and electromechanical punched card methods and now by computers.


9/63

9

The four functions which follow are all that a computer can perform but they also

include most data processing steps:

i) Input / Output operation:A computer can accept data(input) from and

supply processed data(output) to a wide range of input/ output devices.

Such devices as keyboards and display screens make human - machine

communication possible. Multiple output documents may be reproduced

by printers.

ii) Calculation operations:The circuits in a computer are designed to permit

addition, subtraction, multiplication and division.

iii) Logic/ Comparison operation: The computer also has the ability to

perform certain logic operations. For example, when two numbers

represented by the symbols A and B are compared, there are only 3

possible outcomes:

1) A is equal to B ( A=B);

2) A is greater than B (A>B) or

3) A is less than B (A


10/63

10

This comparison ability makes it possible to classify item A is having or

not having the characteristic of B. This simple ability to compare is an

important computer property because more sophisticated questions can be

answered by using combinations of comparison decisions.

iv) Storage and retrieval operations: Both data and program instructions

are stored internally in a computer. Storing both data and instructions in

same memory is known as stored program concept or John Von

Neumann Concept. And once stored, both may be quickly called or

retrieved for use. The time required for data to be retrieved is measured

in micro-or nanoseconds.

1.6 TYPICAL PC CHARACTERISTICS

Some of the major characteristics of a typical personal computer are summarised

below. This should give a glimpse of a desktop computer and introduce you to some of

the terms used with personal computer.

FEATURE TYPICAL BRIEF DESCRIPTION

CPU type 8088, 80286, 80386, 80486,Pentium-I, II, III

The CPU determines howmuch memory the system

can address, what kind of

software it can run, and

how fast it can go

Bus type PC Bus (8-bit ISA), AT Bus(16-bit ISA), Proprietary

32-bit Micro Channel,EISA, Local or VESA bus,

PC-Card, PCI

The bus determines whatkind expansion circuit

boards will work in themachine. Most buses are

incompatible with theothers (exception: EISA

bus computers can use ISA

cards), which makes itimportant that you know

which kinds of boards

youre buying

BIOSmanufacturer

American Megatrends, Inc(AMI), IBM, Compaq,

Phoneix, Award

BIOS (Basic Input/OutputSystem) is the low-level

system software that

determines how

compatible your computeris.

CPU Speed 4.77 MHz (PC speed) upto

200 MHz

Megahertz (MHz) is a

rough measure of system


11/63

11

speed. All other thingsbeing equal, a 10 MHz

machine is faster than a 5

MHz machine. (All other

things generally arent

equal)Video board Monochrome Adapter

(MDA), Color/Graphics

Adapter (CGA), EnhancedGraphics Adapter (EGA),

Video Graphics Array

(VGA) 8514 Adapter,

Extended Graphics Array(XGA), Diamond Viper

ATI Mach 32.

The video board affects

what kind of software you

can run and how quicklydata can get on the screen.

It can be easily changed,

and the oldest PC can use

anything from amonochrome board up to a

VGA or 8514. Changing

video boards may require

updating software to usethose video boards. Video

boards vary by the numberof colors and pixels (the

dots on the screen) that

they can display. Most

important in modern videoboards, however, is

whether they hold video

data as a simple Dumb

frame buffer which

requires that the CPU mustdo all the video work, or

contain circuitry that canhelp with the grunt work

of graphical screens:

boards like that are said to

be bitblitter boards.

Parallel port Unidirectional, Bi-directional, EPP (Enhanced

Parallel Port)

The parallel port acts asthe basic interface for

printers. In its simplest

form, its unidirectional.

More modern parallelports may support bi-

directional data flow, ormay even support higher

speeds of data

transportation, known as

an Enhanced Parallel Port,usually abbreviated EPP.


12/63

12

Bi-directional parallelports are more and more

essential in order to

support newer printers,which work their best

when teamed with a bi-directional or, better, EPP

port.

Serial port UART 8250, 16450, 16550 The UART is the mainchip around which a serial

port or internal modem is

built. The 16550 UART is

the fastest of the lot, and isessential for high speed

communications and

communications in

multitasking environments.Amount of

memory

640K - whatever There are several kinds of

memory or RAM (Random

Access Memory)conventional, extended,

and expanded. They all

solve different problems.

Some software wont runwithout a particular

amount of one or more ofthese kinds of memory.

Most PCs come with 64 or128 MB of RAM.

System Clock /Calendar

Built on motherboard oradded on expansion board.

Again, not terriblyimportant. Machines with

built in clocks usually have

DIS support to directly

read from or modify thetime and date. Others

must run a separate

program.

Hard diskinterface ST506/412, ESDI, SCSI,IDE, EIDE What method does thehard disk controller (acircuit card in the system)

use to talk to the hard

disk? This affects speedand can be easily changed

in most systems. Modern

systems use IDE or SCSI;


13/63

13

SCSI is preferable for itsflexibility.

Hard disk

encoding scheme

MFM, RLL, ARLL How much data is

squeezed on to the area on

disk called a track? These

methods are used tosqueeze more data onto a

hard disk, and can easily

be changed.

Keyboard type XT-type, AT-type IBM originally put a

keyboard control chip in

the keyboard for the PC

and XT. They moved it tothe motherboard for the

AT, so youve got to know

which kind of keyboard

interface youve got. Mostclone keyboards have a

switch allowing them to

swing both ways.

Floppies

supported

5.25 inch 360 K, 1.2MB,

720K (Unusual); 3.5inch

720K, 1.44 MB, 2.88MB

What kind of floppies will

your machine support?

This can be changed fairly

easily.

Number ofexpansion slots

3-10 The more, the merrier.Many bit-name computers

only sport three expansionslots; look instead for theeight-slot models.

Configuration

method

Switches configuration

(CMOS) memory

Computers wont work

until you tell them about

themselves, or configure

them. Its done with eitherphysical switches or

software.

Number of

interrupts (IRQ

levels) supported

8 or 16 Affects the number and

type of expansion boards

in a system.Number of DMA

(Direct Memory

Access) channels

supported

4 or 8 Affects the number and

type of expansion boards

in a system.

Sound Card 8 or 16 bit FM, MIDI,and/or wavetable Audio

interface

Sound boards supportmusic and sound

reproduction on your PC,


14/63

14

but music and sound arerepresented in either an 8-

bit or a 16-bit format. 16-

bit is better, but takes morespace. The sounds are

recorded and reproducedeither with FM synthesis,

MIDI control, orwavetables. Additionally,

a sound card in

combination with a CD-

ROM can play music onyour PC, with the right

audio interface cable.

SCSI host

adapter

SCSI-I or SCSI-II single

ended or differential;

normal, fast, wide, orfast/wide

SCSI is a kind of universal

hardware interface that

allows you to put harddisks, CD-ROMs, tape

drives, optical drives, andscanners onto your

machine with a minimum

of hookup trouble. SCSI is

still an evolving standard,but with many choices

Most PCs dont have

SCSI, but most couldbenefit from adding SCSI;

all you need is the SCSIhost adapter board and

some software.

LAN board Ethernet, Token Ring andARCNet

Local area networks(LANs) allow PCs to

communicate with one

another, share data and

printers. Each PC on aLAN needs a LAN

transceiver card, and there

are three types: Ethernet,

Token Ring, and ARCNet.Ethernet is the most

common. Most businesseshave LANs, and more and

more homes are adding

LANs as they acquire PCs.

CD-ROM Drive Spin speed (internal or

external) SCSI, IDE or

support CD-ROM disks,

which can hold almost 700


15/63

15

proprietary interface MB of data. More andmore software ships solely

on CD-ROM, making this

item a necessity. Theyvary largely by whether

theyre internal or external,and how quickly they can

transfer data to a PC.Transfer speeds range

from 150K/s (single

spin), 300K/s (double

spin), 450 K/s (triplespin), to 600 K/s (quad

spin), 900 K/s (six

speed). 1200 K/s (eightspeed, 1500 K/s (ten

speed) CD-ROMinterface either by way ofIDE or a SCSI host adapter

or by way of a proprietary

adapter.

Printer Control

language

Epson codes, HPPCL

(Laser jet commands) PostScript others.

Printer control languages

tell your printer how tounderline words, put

pictures on the page, and

change typefaces.


16/63

16

1.6 QUESTION/ ANSWER KEY

1.A _____________________ is a fast and accurate electronic ( or data)

manipulating system that will accept and store input data, process them and

produce output results.

2._________________________ are facts or informational raw materials

represented by symbols

3.Arranging classified data in a predetermined sequence to facilitate processing is

called ______________________.

4.The word " data" is the plural of datum which means __________________.

Answers:1. Computer 2. Data 3. Sorting 4. Fact

Mark True or False

True False

1. Electrical or electromechanical components are known as hardware.

2. A Program is considered as hardware

3. Keyboard is considered as output device

Answers:

1. True 2. False 3. False


17/63

17

Chapter 2

COMPUTER SYSTEMORGANIZATION

STRUCTURE

2.0 Introduction

2.1 The System Concept

2.2 Organization of Computer System

2.2.1 Input Devices

2.2.2 Central Processing Unit (CPU)

2.2.3 Output Devices

2.3 Computer Limitation

1.1Classification of Computers

1.2Question/ Answer Key

2.0 INTRODUCTION

Lets take a look at our computer definition. A computer is a fast and accurate

symbol manipulating system that is organized to accept, store, process and produce

results under the direction of a stored program of instructions.

This section explains the computer is a system and how a computer system is

organized. Organization of computers input devices, Keyboard, mouse and classification

of Computers.

2.1 THE SYSTEM CONCEPT

The system is a group of integrated parts that have the common purpose of achieving

same objectives. The following characteristics are important:


18/63

18

1. A group of parts : A system has more than one element. A steel ball is not a

system but it might be part of a bearing assembly that could be combined with

other components to produce an irrigation system.

2. Integrated parts: A logical relationship must exist between the parts of a

system, mechanical and electronic systems such as washing machines and

video games have components that work together. And a personal

management system may consist of integrated procedures for recruiting

training and evaluating employees.

3. Common purpose of achieving objectives: The system is designed to

accomplish one or more objectives, all system elements should be controlled

so that the goal is achieved. Totally automated systems have highly

controlled operations, systems operated by people sometimes get out of

control.

A computer is a group of integrated parts that have the common purpose of

performing the operations called for in the program being executed it is also a

system. Any system may be comprised of smaller systems or subsystems.

A subsystem is a smaller system contained within a larger one. The

component parts found in most computer system ex: printers are systems in a

way and computers in small may be considered subsystems in larger

supersystems such as air traffic control system.

2.2 ORGANIZATION OF COMPUTER SYSTEM

Input central output

Devices processing unit devices

Fig. 1 Overview of Processing

The figure above shows the basic organization of computer system. The system

included input, processing and output devices. Let us see each component of the system

in more details.


19/63

19

2.2.1 Inpu t Devic es

Computer systems use many devices for input purposes. Some allow direct human/

machine communication. The keyboard of a workstation connected directly to or online

to a computer: Devices that read data magnetically recorded on specially coated plastic

tapes or floppy plastic disks are popular. Regardless of the type of device used, all are

components for interpretation and communication between people and computer systems.

There are few important input devices which we will learn in details.

Keyboard: Is the most friendly input device through which data programs are keyed

in and certain commands to software can be given from the keyboard.

The keyboard consists key switches there is one key switch for each letter, symbol

number etc. much like a typewriter when a key is pressed, the key switch is activated.

The keyboard has an electronic circuit to determine which key has been pressed. Thenthe 8-bit binary code is generated and sent to the computers. The binary code may

be an ASCII ( American Standard Code for Information Interchange), EBCDIC (

Extended Binary Coded - Decimal Interchange Code) or Hex code.

Fig. 2 Key Board

Keyboards are classified into two types depending on the number of keys present in

them.

a) Ordinary Keyboard: consists of 86 keys.

b) Extended Keyboards: consists of 101 keys ( Windows ready )

Computer Keyboard


20/63

20

Keyboards are of two types based on the fashion of data transfer.

a) Serial Keyboard: It sends the data, bit by bit in a serial fashion and the computer

converts the data into a parallel type.

b) Parallel Keyboard: It sends the data as a byte in parallel form, the bits are sent

simultaneously on different lines( wires).

Mouse:A mouse is a graphical input device the term mouse is used because of its

shape. The mouse has two or three buttons on its top. The function of each button is

defined by the software. The mouse also has a small rotating ball at the bottom. When

the mouse is moved on a rubber pad, the ball rolls whose movement is converted into an

electrical signal and seat to the CPU on the CPU this movement is interpreted and

displayed on the screen of the monitor (CRT) in the form of movement of the arrow mark

. This movement of arrow mark is used to highlight the graphical index on the screen.

When a desired command shown on the screen is approached by the arrow mark due to

the movement of the ball in the mouse the click button is pressed to highlight the same.

Fig. 3. Mouse

There are 2 methods by which a mouse is connected to a computer serial interface

and parallel interface.


21/63

21

2.2.2 CENTRAL PROCESSING UNIT (CPU)

The heart of any computer system is the CPU. Three main sections are generally

located within computers of all sizes.

a) The Primary Storage Section: This section is used for four purposes.

1. Data are fed into an input storage area where they are held until ready

to be processed.

2. A working storage space that holds the data being processor and the

intermediate results of such processing.

3. An output storage area holds the finished results of the processing

operations until they can be released.

4. In addition to these data-related purposes, the primary storage section,

also certains program storage area that holds the processing

instructions.

In addition to primary memory storage or main memory section most

computers also have secondary storage capabilities ( like hard disk,

floppy disk )

b) The arithmeticlogic section:

All calculations are performed and all comparisons (decisions) are made in

the arithmetic logic section of the unit are temporarily placed in a designated

working storage area until needed at a later time data may thus move from

primary storage to the secondary storage many times before the processing is

finished. Once completed, the final results are released to an output storage

section and from there to an output device.

c) Control Section :

The control section maintains order and directs the operation of the entire

system. Although it does not perform any actual processing on the data, the

control unit acts as a central nervous system for the other components of the

computer. At the beginning of processing, the first program instruction is selected

and fed into the control section from the program storage area. There it is


22/63

22

interpreted, and from their signals are sent to other components to execute the

necessary actions.

2.2.3 OUTPUT DEVICES

Output devices:- Like the input devices, output devices are instruments of

interpretation and communication between humans and the computer system. Printer is

Considered as output device.

All input/output and secondary storage units are sometimes called peripheral devices.

2.3 COMPUTER LIMITATIONS

Computers although they are very useful, they have some limitations.

i ) Programs mu st be rel iable:

As a machine, the computers does what it's programmed to do and nothing else.

This doesnt mean that it must be stupid clever programs can be written to direct the

computers to store the results of previous decisions. But a seemingly flawless program

that has operated without a problem for months can suddenly produce non-sense. A

reliable program thats supplied with incorrect data may also produce non-sense.

i i ) App l icat ion logic mu st be understood:

The computer can only process applications which can be expressed in a finite

number of steps leading to a previously defined goal. Each step must be specifically and

clearly define, if the steps in the problem solution cannot be precisely stated, the job

cannot be done. The computer may not be of much help to people in areas where

qualitative material or evaluation is important.

For example, The market decision may be of a qualitative nature because sales

volume data may rest on future social, political, technological and economical events.

However, the computer can let the manager know how the product will fare underassumed price, cost and sales volume condition.

i i i ) App l icat ions mu st be sui table:

Writing programs is a human task it can be time consuming and expensive. Thus,

non-recurring jobs are often not efficient areas for business data processing applications.


23/63

23

Rather as a general rule its most economical to prepare business programs for large-

volume, repetitive applications such as payrolls that will be used many times.

2.4 CLASSIFICATION OF COMPUTERS

Computers are classified by the type of data they are designed to process. Data may

be obtained either as a result of counting or through the use of same measuring

instrument. Data that are obtained by counting are called discrete data, examples of

discrete data are total number of students in a classroom. Data that must be obtained

through measurement are called continuous data. For example, of continuos data are the

speed of an automobile measure by speedometer or the temperature of a patient as

measured by a thermometer.

A digitalcomputer is a counting device that operates on discrete data. It operates by

directly counting members ( or digits ) that represent numerals, letters or other special

symbols. Just as digital watches directly count off the seconds and minutes in an hour,

digital processors also count discrete values to achieve the desired output results.

In contrast to digital processors, however, there are also analog machines that do not

compute directly with numbers. They deal with variables that are measured along a

continuo scale and are recorded to some predetermined degree of accuracy. Temperature

for example may be measured to the nearest tenth of a degree on the Celsius scale,

voltage may be measured to the nearest of hundredth of a volt. A service station petrol

pump may contain analog processor.

Analog computers may be accurate to within 0.1 percent of the correct value. But

digital computers can obtain whatever degree of accuracy is required simply by

calculating additional places to the right of the decimal point. For example; A pi( ) has a

value of 3.1416. Actually the true value of pi is 3.14159.... ( this number could go on for

pages)

Desirable features of analog and digital machines are sometimes combined to create

a hybrid computing system in a hospital intensive-care unit, for example analog devices

may measure a patients heart function, temperature and other vital signs. These

measurements may then be convicted into members and supplied to a digital component

in the system.

Classification of computers based on their size, cost & configuration.


24/63

24

In this category computers are classified as micro-computers, mini computers, main

frame computers, home computers and super computers.

Micro Computers:

A Micro computer is the smallest general-purpose processing system that can

execute program instructions to perform a wide variety of tasks.

The important features of micro computers are:

1. Micro computers are known as home computers, personal computers, desktop

computers and small business computers.

2. These are small, low-cost digital computer with a micro processor as its CPU,

a memory unit an input device and an output device.

3. The word length of a micro-computer lies in the range of 8-32 bits.4. CPUs are in a single chip

5. Storage capacity is small

6. Applications include general-purpose calculations, industrial control, office

automation etc.

Personal Computers (PCs):

Personal computers are micro-computers for general-purpose computations. These

are classified as PC, PC/XT, PC/AT and super AT (or super micro) based on their cost

and configuration. All these types contain a CPU,RAM,ROM,CRT display, Keyboard

and secondary memory.

Features:

1. PC is the simplest and cheapest type of computer and it uses an INTEL 8088 (

micro processor chip) as CPU, 640 KB, RAM, 8KB ROM ( ROM can be

extended upto 64 KB) and floppy disk as secondary memory; processing

speed of a PC lies in the range 1-5 MIPS ( micro-instructions per second )2. PC/XT ( Personal computer extended technology) contains hard disk, floppy

disk drives ( 360/1.2 MB), Intel 8088 CPU, 640 KB RAM and 8 KB ROM.

This is costlier than a PC because of the hard disk it contains. PC/XT is a

single user system. Processing speed of a PC lies in the range 1-5 MIPS and

hard disk capacity lies in the range 20-80 MB.


25/63

25

3. PC/AT ( Personal computer advanced technology) contains. Intel 80286 as

CPU, 640 KB RAM (expandable to 4 MB), 64 KB ROM (expandable to 128

KB), hard disk drive and floppy disk drive (360 KB/1.2 MB), its CPU is

powerful than the CPU of PC/XT and four to five terminals can be connected

to it to make it multiuser. Processing speed of PC/AT lies in the range 1-5

MIPS and hard disk capacity lies in the range 20-80 MB.

4. Super AT( or super micros) uses a 32-bit CPU, Intel 80386 & 80486. The

RAM capacity of super macros lies in the range 2-8 MB in 80386 CPU can be

extended upto 32 MB and in case of 80486 upto 64 MB. The hard disk

capacity of super macro lies in the range 200 800 MB. The processor speed

of 80386 CPU lies in the range 3-5 MIPS and that of 80486 CPU is 12 MIPS

to 25 MHz clock UNIX is used as operating system.

The processing speed of home computers and microcomputers for industrial

control is less than 1 MIPS. Home computers are used for entertainment,

basic education and home management and income tax calculation,

investment analysis etc..

Mini Computers:

The salient features are:-

1. The word length is 32 bits and their processing speed lies in the range 10-30

MIPS.

2. RAM capacity lies in the range 8 MB 96 MB ( in same it can be extended

upto 128-256 MB)

3. The hard disk capacity lies in the range 380 MB2GB ( gig bytes)

4. Most mini-computers use Motorola 68030 and 68040 CPU.

The Minicomputers which are faster and more powerful than microcomputers can

support upped 64 or even 100 terminals and some minicomputers are Uni. Processor and

some others are multi processor systems. These are used for payroll preparation and

scientific computation, multi-user and interactive applications in college universities

research organizations, industries, sophisticated real time(industrial) control, interactive

engineering design work etc..


26/63

26

Examples of mini computers are:

IBMAS/400/B60

VAX8842(VAX stands for Virtual address)

Extension - VAX computers are manufactured by Digital Data

Corporation)

WIPRO S68030V & S-6833V built around 68030 CPU

WIPRO LANDMARK 860 ( a super mini) built around Intel i860-

CPU

HP 9000 series 800 ( super mini) built around Hewlett Pacards

VLSI RISC processors

HCL magnum built around 68030 CPU and 68040 CPU.

4. Main-frame Computers:-

The mainframe computers are faster and more powerful than mini computers. These

computers are used where large amount of data are to be processed or very complex

calculations are to be made and these tasks are beyond the computing capacity of mini

computers.

The main features are :

The word length may be 48, 60 or 64 bits.

Memory capacity range is 64-256 MB and hard disk capacity is

1000 MB10 GB or more.

Processing speed lies in the range 30-100 MIPS.

The mainframe computers are used in research organizations, large industries,

business organizations, government organizations, banks and airline reservations etc..

Example: IBM 4300 series

IBM 308X series

Latest model IBM 3090 series

IBM 9000 series


27/63

27

HP 9000 series 8705/400

HP 9000 model 8705/300

5. Supercomputers:

The salient features are :

1. Their word length is 64-96 bits; memory capacity is 256 MB & more; hard

disk capacity 1000 MB and more

2. Processing speed lies in the range of 400 MIPS 10000 MIPS. In a single

machine cycle tow 64bit data can be added

Super computers are much faster and more powerful than mainframe computers.

Super computers are specially designed to maximize the number of FLOPS ( FloatingPoint Operations Per Second). Their FLOPS rating is usually more than igiga flops per

second. A super computer contains a number of CPUs which operate in parallel and

make it faster. They are used for massive data processing & solving very sophisticated

problems.

They are used for weather forecasting weapons research and development, rocket

launching, seismology, atomic, nuclear and plasnia physics.

Example:-

CRAYXMP/14, X-MP/24 & X-MP/48

CRAYMP, CRAYZ, CRAY3, CRAY Y-MPC

ETA 10 ( Developed by control data Corporation )

SX2 (Developed by Nippon Electric Corporation, Japan)

SX3R ( 25.6 GIGA FLOPS )

HITACS300 ( 32 GIGA FLOPS, HITACHI MAKE )

2.5 QUESTION / ANSWER KEYS

True False

1. Digital Computer Operates on continuous data

2. Random access memory is secondary storage memory


28/63

28

3. Classification of computers done depending on size, cost and

Configuration.

4. CRAY XMP/14 is a minicomputer

Answers :

1. False 2. False 3. True 4. False


29/63

29

Chapter 3

SOFTWARESTRUCTURE

3.0Introduction

3.1Software

3.1.1 System Software

3.1.2 Application Software

3.2Machine Language3.3Assembly Language

3.4High Level Language

3.5Question/ Answer Key

3.0 INTRODUCTION

Software is a set of instructions to perform a task. Hardware is an electrical or

electromechanical components of a computer. Software and hardware plays an important

role for a computer. This unit discusses software and types of languages used on a

computer.

3.1 SOFTWARE

Software is defined as a set of programs that activate the hardware of the computer.

A program is nothing but as sequence of instructions where each instruction is a

command given to the computer to perform a certain specified operation or given data.

Software can be classified into two parts:

1. System Software

2. Application Software

3.1.1 System Softw are

It is a collections of programs executed as needed to perform functions such as:

i) Receiving and interpreting user commands.


30/63

30

ii) Entering and editing applications programs and storing them as files in

secondary storage.

iii) Controlling I/O units to receive input information and produce output

results.

iv) Translating programs from source from entered by the user into object

from consisting of machine instructions.

v) Linking and running user written applications programs with

standard routines that exist on the system.

The system software consists of operating system, assembler, compiler, interpreter,

debugging programs, text editors etc..

3.1.2 Ap plication Softw are

An application software is the software that has been written to processor perform a

specific job.

Example: Word processing packages for processing and manipulating text,

spreadsheet packages for calculating finances and data analysis, CAD for designing and

drafting etc..

3.2 MACHINE LANGUAGE

A computer understands information composed of only zeros and ones hence it uses

binary digits for its operation. A program written in the form of 0s and 1s is called

machine language program. There is a specific binary code for each instruction. For eg:

to add the contents of register A and register B, the binary code is 10000000 for Intel

8085 microprocessors. The binary code for certain operations differs from computer to

computer.

3.3 ASSEMBLY LANGUAGE

Writing programs in machine language is very difficult, tiresome and boring job for

a programmer, it is error phone. To solve this problem and to facilitate programmer

easily understandable languages have been developed. Assembly language is one of

them. Programs can easily be written in alphanumeric symbols instead of Zeros & Ones

meaningful and easily remarkable symbols are selected for this purpose.


31/63

31

Example: ADD, for addition, SUB for subtraction CMP for comparison.

Such symbols are called mnemonics. A program written in mnemonics is called

assembly language program.

Assembler

A program which translates an assembly language program into a machine language

program is called an assembler.

Assembly languageAssemblerMachine language

(Source Program) (Object program)

Disadvantages

1. Programming is difficult and time consuming

2. The assembly language is machine oriented i.e the programmer must have theknowledge of the hardware of the computer

3. The program written in assembly language for one computer cannot be run on

another computer

3.4 HIGH LEVEL LANGUAGES

A High level language is one which is expressed in terms of simple English like

language.

The instructions written in high level language are called statements. The statements

more clearly resembles English Mathematics as compared to mnemonics.

Example:

BASIC, PASCAL, FORTRAN, COBOL, ALGOL, LISP, ADA, SNOBOL

Advantages

1. They are easier to learn as compared to assembly languages.

2. They make programs easier and faster to write

3. Provide better documentation.

4. The programmers does not have limitations to use a single type of machine.

5. Programs are portable i.e. they will run on any computer

Many high level languages have been developed, some are for general purpose and

some for special purposes.


32/63

32

Example:

PASCAL, PL/1, ADA AND C are general purpose languages.

COBOL is for business purposes

PROLOG is for logical reasoning

BASIC for new comers

SNOBOL for text processing

Source language and Object language

The language in which a programmer writes programs is called source language. It

may be high-level or assembly language. The language in which the computer works is

called object language or machine language.

Compi ler

A program which translates a high-level languages into a machine language program

is called compiler. For example, WATFOR (FORTRAN compiler ), TURBO PASCAL

compiler.

Interpreter

An interpreter is a program which translates statements of a high level language

program into machine code.

In translates one statement of the program at a time. It reads one statement of a high-

level language program translates it into machine code and executes it. Then it goes to

the next statement.

On the other hand a compiler translates the whole program into machine code-

Highlevel Compiler Machine

Language or Interpreter language

(Source (Object

Program) program)


33/63

33

3.5 QUESTION/ ANSWER KEYS

State True or False:

1. Machine language is one which is expressed in terms of 0's & 1's.

2. Assembly Language is one which is expressed in terms of mnemonics

3. Compiler is a software which converts machine language to high level

Language.

4. Fortran is a low level language.

Answers :

1. True 2. True 3. False 4. False.


34/63

34

Chapter 4

PRINTERSSTRUCTURE

4.0 Introduction

4.1 Objectives

4.2 Printers

4.3 Types of Printers

4.4 Check your progress

4.0. Introduction

This deals with computer hardware that are used for outputing data from a computer

and it also introduces various types of printers.

4.1. Objectives

The objectives of this unit are

To introduce computer hardware which forms the essential components

of a computer system.

Which provides hard copy of the output.

4.2 Printers

One of the most convenient and useful methods by which the computer can deliver a

hard copy is by means of printing. For the sake of convenience, the printer should have

the ability to print alphabetic character, decimal digits, and common punctuation marks

etc..


35/63

35

Funct ions of a Pr inter

The printer receives data characters from the computer and prints the characters on

the paper. In addition, the printer also receives control characters from the computer.

These control characters are not printable characters. They convey some sort of control

information to the printer ( bold, italic underline etc.). Some of the control characters

widely used are:

CR(Carriage Return) : Specifies that the pointer head carriage should return to the

first print column. Any subsequent data character received will be printed starting from

the first column.

LF(Line Feed): informs the printer to skip one line on the paper.

FF (Form Feed): Instructs the printer to skip the paper to the beginning of the next

page or form. In addition to these the printer has to send acknowledging signal back tothe computer indicating the status.

Basic c haracter ist ics of a pr inter :-

1. Speed: Specified as CPS ( Character Per Second ) or LPM ( Lines Per

Minute ). It indicates how fast a printer works.

2. Quality:Specified as DRAFT, NLQ ( Near Letter Quality ) or LQP ( Letter

Quality Printer). This give how good the shape of the printer character is.

3. Character Set: Indicates the total number of data characters and control

characters recognized by the printer. The normal ASCII and EBCDIC.

4. Interface: Specifying whether the printer receiving characters from the

computer in parallel form or in serial form.

5. Buffer size:Indicates how many data characters can be stacked in the printer

buffer memory before printing.

6. Print size:Specified as character size and number of characters per line.

4.3. Types of printers

There are several types of printers that are designed for different types of

mechanisms based on the approach of printing and speed; printers may be classified as:

1. Character printers


36/63

36

2. Line printers

3. Page printers

Printers are also classified as:

1. Impact printers and

2. Non-impact printers

Impact printers: The printers which use the familiar type written approach of

hammering a typeface against paper and inked ribbon are called impact printers.

Non-impact printers:The printers which do not hit or impact a ribbon to print, are

called non-impact printer such printer uses thermal, electrostatic, chemical and inkjet

technologies.

Character printers: This category of printers generally function in the same way

as a typewriter. There are many types of character printers some of them are:

Daisy-wheel printers: In daisywheel printer the raised letters are attached at the

ends of spokes of a wheel. A motor spins the wheel at a rapid rate. The wheel is rotated

until the desired letter is in position over the paper and then solenoid-driven hammer hits

the spoke against the ribbon to print the letter. The daisy-wheel printers are impact

printers. The advantages of the daisy-wheel printers are high print quality,

interchangeable fonts and print speed upto 55 characters per second. However the print

quality is not as good as that produced by the spinning golf ball.

Fig 4.1 Daisy Wheel Printer


37/63

37

1. Spinning golf ball printers: This also function in the same way as a daisy-wheel

printer. The main difference in the mechanism is that the entire character set is

present as raised type around a sphere.

The bottom of the sphere is connected to the motor drive mechanism. The ball can be

easily shifted up or down, rotated and tilted until the character to be printed can be

precisely positioned over the desired location on the paper. For printing the letter on

the paper, the spinning golf ball is hit against the ribbon. The head is moved across

the paper to print a string of characters.

The advantages of spinning golf ball printers are excellent print quality and easy

interchangeability of fonts. However, this type of printers posses some disadvantages

too, i .e it is mechanically complicated and noisy mechanism. It has low speed about

14 character per second.

2. Line printers:Are most suitable for massive data with higher speed of printing:

Fig. 4.2 Line Printer


38/63

38

Drum pr inters:-

A drum type printer consists of a rapidly spinning drum which has a complete raised

character set constructed around it for each character position across the paper.

Each band contains all the possible characters, Magnetically driven hammers are

provided in each character position to hit the paper and ribbon against the spinning drum

for printing the desired characters. An entire line of characters can be printed during each

rotation of the drum.

With the help of the drum printer upto 2000 lines/min can be printed. The quality of

printing is not good and there is also high noise pollution.

Drum printers are also called line printers.

Chain pr inters:

A rapidly moving chain called print chain is used in chain printers.

Each link of the print chain is a character's font. For printing a character, a print

hammer is located behind the paper. As the print chain rotates, the properly timed

hammers strike the paper and the ribbon together against the desired character set several

times on the chain, the speed of chain printers can be improved. Speed of chain printers

reaches upto 2500 characters per minute.

Dot-Matr ix Impact prin ters:

A dot-matrix printers each character as a pattern of dots. The print head comprises a

matrix of tiny needles having seven rows with nine needles in each row. The tiny needles

hammers out the characters in the form of patterns of tiny dots. The print needles are

Fig 4.3 Printing Cylinder of a Drum Printer


39/63

39

arranged in a vertical column so that characters are printed out one dot column at a time

as the print head is moved across the line. The quality of the print is not so good.

However the quality of printing can be improved by printing a line twice with the dots for

the second printing offset slightly from those of the first. Print speed of dot matrix impact

printers is max of 350 cps.

Page printers:The page printers are non-impact printers having speeds over 20,000

lines per minute. The technique called Electro-photographic technique is developed from

the paper copier technology. The important type of page printers are:

1. Electromagnetic printers:

The magnetic recording technique is used in this type of printers. A

magnetic image of the matter to be printed is written on a drum surface.

The surface of the drum is then passed through magnetic powder which

adheres only to the charged areas. This powdered surface is now pressed

on to the paper to obtain the hard copy of the data. Speeds of

electromagnetic printers upto 250 characters per second may be obtained.

2. Electrostatic printers:

In such printers, a paper coated with a non-conducting electric material

which holds the charges of voltages are applied with writing heads, is

used, The heads( or nibs) write dots on the paper as it passes. The paper is

now passed through a toner which contains material with particles

carrying an opposite charge to that of that of the paper written by the nibs.

The particles adhere to the magnetized areas and form printed characters.

3. Laser and xerographic printers:

The principle of laser printers and xerographic printers, is almost the

same, The image of the page to be printed in first formed on a

photosensitive drum in the printer. Powdered ink or tones is applied to the

surface of the drum. Now, the image from the drum is electrostatically

transferred to the sheet of paper. The ink image on the paper is finally

fused by heating process internally.

In case of a laser printer, the image on the photosensitive drum is

produced by a laser beam. The laser is swept backs and forth across the


40/63

40

drum to produce an image in the same way as produced on a roaster scale

CRT. The rotating mirror sweeps the laser beam across the rotating drum,

With the help of a modulator controlled by a microcomputer, the laser

beam is turned on or off to produce dots. After the image is inked and

transferred to the paper, the drum gets cleaned and gets ready for the next

page. The speeds of laser and xerographic printers are to the tune of

20,000 lines per minute. The quality of print is also good.

4.4 CHECK YOUR PROGRESS

1. Pick up the correct statements from the following:

a) Typical speeds of drum printers may be in the range of 300 to 2000 lines per

minute.

b) Typical speeds of chain printers may be in the range of 400 to 2500 characters per

minute.

c) Typical speeds of page prints may be even more than 20,000 lines per minute.

d) All the above.

2. Printers:

a) are most commonly used o/p device

b) are used to prepare permanent documents

c) are of several types

d) all the above

Fig 4.4 Laser Printer


41/63

41

3. The impact printers use:

a) Thermal technology

b) Chemical technology

c) Electrical technology

d) None of the these

4. Drum printers is a:

a) Line Printers

b) Letter Quality Printers

c) Dot-Matrix Printers

d) None- of the above

5.The primarily used computer device for obtaining the hard copy is:

a) Line Printers

b) CRT

c) Keyboard

d) None

State whether the fol low ing statements are correct :

1. The daisy wheel printers are called non-impact printers

2. Line printers are impact printers

3. A printer produces a hard copy

4. Line printers print an entire line at a time

5. A Daisy wheel printer is character printer

Answers: I

1(d) 2(d) 3(d) 4(a) 5(a)

II

1)False 2) True 3) True 4) True 5) True


42/63

42


43/63

43

Chapter 5

MEMORYSTRUCTURE

5.0 Introduction

5.1 Objectives

5.2 Types of Memory

5.3 Accessing Methods

5.4 UPS

5.5 Check Your Progress

5.0 Introduction

Memory of a computer deals with storage of information. The secondary storage

devices, which retains information in the absence of electrical power are also discuss.

5.1 Objectives

To introduce devices for storing information ( Volatile and Non-volatile )

UPS provides the back up during power failure

5.2 Types of Memory

The memory is used for storing information. It is classified into two groups

1) Primary memory and

2) Secondary memory

Primary memory: is generally termed as computers memory, the main memory.

The primary or internal storage is a most essential part of all computers. The internal

storage area is made up of several small storage areas called locations or cells. Each of

these locations can store a fined number of bits called word length of that particular


44/63

44

storage unit. Each location or word has a built in and unique number assigned to it. This

number which is used to identify the location, is called the address of the location.

The primary memory actually functions when the computer operates and is

present in the computer in two different forms RAM & ROM.

Random Access Memory (RAM): The primary storage is generally referred to as

random access memory (RAM) because one can select and use any location of this

memory to directly store and retrieve data instructions. Every location of the memory is

easily accessed and time taken in each case is same.

The facility of read/write from a RAM chip entitles it to call read/write memory.

When the power is switched off, the information stored in RAM is lost.

Read Only Memory (ROM): In this memory storage information is permanently

stored. The information contained in can only be read and not written fresh informationinto it. When power is switched off the information stored inside a ROM is not erased,

ROM memories are also known as fieldstores, permanent stores or dead stores.

Cache Memory: A very high speed memory used to increase the speed of

processing is employed between CPU and main memory whose access time is close to

the processing speed of the CPU. This type of memory is called a high-speed buffer or

cache memory. However, cache memory is not addressable by the user of the computer

system.

Cache memory makes the main memory of the computer appear to be faster and

larger than what it really is. The cache memory is normally very small due to its high

cost of construction, cache memory improves the memory transfer rate and also increases

the processor space.

5.3 Accessing Methods

The memory of a computer is not actually concentrated in one place, Storage

devices are scattered throughout the machine. For instance, the operation registers are

flip flop registers which are used in the arithmetic and control units of the computer.

The storage devices are used to introduce information to the computer from the

outside world and to store results from the computer. The procedures for locating

information may be divided into two classes:

1. Random access storage devices and


45/63

45

2. Sequential access storage devices.

A random access storage devices :is one in which any location in the device may

be selected at random access to the information stored in direct and approximately equal

access time is required for each location.

A sequential access storage device: is one in which the arrival at the location

desired may be preceded by sequencing through other locations, so that access time

varies according to location.

For example, If we try to read a word stored on a real of magnetic type and the piece of

tape on which the word is stored is near the center of the reel, it is necessary to sequence

through all the intervening tape before the word can be read.

Another way to subdivide storage devices is according to whether they are static or

dynamic

A static storage: is one in which the information does not change position example

flip flop, tape are of static storage devices.

A dynamic storage: Devices are devices in which the information stored is

continually changing position. Circulating register utilizing change coupled device (

CCD) delay lines are example of dynamic storage devices.

Sequentially Accessed Devices:

Punched paper tape: The paper tapes normally 1 inch (2.54 cms) wide are

available in rolls of different length. Data is coded on the paper tape in the form of

punched hole combinations, The length of the tape may be kept as required by the user.

The information is recorded as holes punched in rows across the width of the tape.

Each row represents one character. The maximum numbers of holes per row is

known as number of channels on the tape. An eight-channel tape is generally used in

computers.

A line of sprocket holes in the middle of the tape is provided for the purpose of

feeding the tape through the tape punching and reading device.

Disadvantages

i) Less numbers of characters can only be stored.

ii) The paper tape media gets easily torn.


46/63

46

Advantages

i) Storage capacity of paper tape is unlimited

ii) Cost per bit stored is very low

Magnetic tape:

This is most popular storage device for large data that are sequentially accessed and

processed magnetic tape is a half-inch (1.27-cm) wide plastic ribbon, which is coated on

the side with an iron oxide material which can be magnetized. The tape ribbon is housed

in a cassette. The computer tape can be erased and reused indefinitely. The stored data

on the tape gets automatically erased as and when fresh data, is recorded in the same area

of the tape.

Recording of information: Information in binary, is recorded on the tape asinvisible magnetized and non-magnetized spots on the iron oxide side of the tape. 0 of

the binary is represented by a non-magnetized spot and 1 is represented by the

magnetized spot on the tape. The tape is divided into horizontal rows called channels or

tracks and into vertical columns called frames. Each character of the information is

recorded per frame based on the code of the computer.

Data transfer rate: The product of tape density and tape speed is known as the data

transfer rate of the magnetic tape. The number of frames per inch length of the tape is

called tape density. The tape density of a magnetic tape is expressed in characters perinch (CPI) or bytes per inch. The tape speed is measured in inches per sec. Data transfer

rate of a magnetic tape may even exceed 1 million bytes per second.

Adv antages of magnet ic storage:

1. The storage capacity of a magnetic tape is unlimited.

2. It possesses high data density

3. Its cost is much less than other data storage devices

4. Its rate of data transfer is high5. It is very easy to handle magnetic tapes

6. It is very easy to transfer information from one place to another.


47/63

47

Draw-backs of magnet ic tapes:

1. As magnetic tape is a sequential access devices, the data recorded on tape can

not be addressed directly. The data item at the end of the tape will require

abnormal access time because all the characters before the data item need by

processed. This is why magnetic tape device is not found suitable in case data

is frequently required to be accessed at random.

2. It is not possible to interpret, the stored data to know the content of the

information.

3. Dust free environment is needed for magnetic tapes and the reel containers.

a) Tape Cassettes: A high quality digital cassette similar in appearance to the home

cassettes.

b) Cartridges: The large cassette which contains long strips of magnetic tape is called

cartridge. It is very convenient to mount the tape there is proper protection against

dirt and contamination.

Both cassettes and cartridges have low data transfer rate, i,e , less than 10,000

bytes/sec.

Random access devices:

Magnetic Disk: It is a thin, circular metal coated on both sides with a magnetic

material similar to a gramophone record. A number of magnetic disks mounted about

half-an-inch apart from each other on a central shaft which may rotate at speed of 2400 or

more revolutions per minute (RPM), consists a disk pack. Magnetic disk packs are the

most popular medium for direct access secondary storage.

Information is stored on both sides of the disks except the upper surface of the top

disk and lower surface of the lower disk. Each face of the disk is divided into a number

of invisible concentric circles called tracks. A set of corresponding tracks in all the

surfaces is called a cylinder. Each track is sub divided into sectors.

Information is recorded on the tracks of a disk surface in the form of minute

magnetic spots. The magnetized spot represents a 1-bit and non-magnetized spot

represents a 0-bit.

The information stored on a disk can be read a number of items and reading

operation is non-destructive. To write a new data, the previously stored data has to be


48/63

48

erased. The storage capacity of a disk pack primarily depends on the number of disks it

contains. The storage capacity also depends on the track per inch of surface and the

number of bits per inch of track.

Magnetic Drum:Magnetic drum is also a direct access storage device that can be

used for both sequential and random processing. It is basically a cylinder with a

magnetizable outer surface. A motor rotates the cylinder on its axis at a rapid speed but

constant rate. The surface of the drum is divided onto a number of tracks upon which

data is stored as magnetized spots similar to that of a disk. Data is stored on the

magnetizable surface of the cylinder as minute magnetized spots arranged in binary form

in the series of parallel circular tracks. Recording of data on the rotating drum and

reading data from the drum is achieved by a set of secondary read/write heads positioned

very near to the drum surface. Writing a new data on the drum erases the previously

stored data simultaneously at that location. Data once recorded on the drum remainsintact until it is erased.

The drum rotates at a speed of few hundred to few thousand rotations per minute

and its access times is fast. Random access is possible to select any particular track of the

drum but once this track is identified, the data is recorded or retrieved sequentially. To

reduce the access time, sometime heads are divided into two sets. Heads are positioned

diametrically opposite i.e for a drum of 20 track 40 heads are provided.

As compared to magnetic disks, data transfer rates are faster. Due to limited storage

capacity, use of magnetic drum storage is on decline.

Winchester Disk: Winchester disk are also used as a storage device. In this unit,

disks are permanently housed and hermetically sealed in contamination free containers.

The disks are coated with a special lubricant which minimizes the friction between the

read/write heads and the disk surface .Computers using these sealed housings are said to

employ Winchester technology. The Winchester technology enables greater precision of

alignment, an increase in the number of tracks on the disk surface and a higher storage

density per track.

Winchester disks are fast and highly valuable and low priced compared with

conventional hard disk drives. They are available in sizes varying form 5.25 to 14 in

diameter and there capacities are 10,12 and 20 megabytes. Dual disk drive doubles the

capacity. Winchester disks are used in large computers.

Floppy Disk: A floppy disk is a circular Mylar disk coated and magnetically

sensitive film. Since the thickness of the Mylar disk is only a few thousandth of an inch


49/63

49

it is named as floppy. The floppy diskette is coated with a magnetic material and enclosed

in a protective jacket. The floppy disks are used for backup of files and to transfer files

from one computer to another computer

Floppy diskettes can be classified as Single and double sided.

If only one side of the diskette is used to store information such a diskette is called as

a single sided disk. If both the side of the diskette is used to store information such a

diskette is called as a double-sided disk.

The diskette surface is logically divided into a fixed number of tracks (concentric

circles). Data can be read and written on the specified tracks and not in between the

tracks. Each track is divided into a number of sectors. The number of sectors in a track

depends on the size.

A read/write head contacts the disk through the head slot to read from or write to the

disk. It is designed such that it can move both forward and backward.

The outermost track is numbered as track 0. The subsequent tracks are numbered

sequentially. The Index hole is used as a reference point to indicate the beginning of a

track.

There is a facility to use a diskette only for reading previously stored information

and to prevent any attempt to write new information on it through the write protect notch.

If this notch is open writing on the diskette is permitted.

Manufacturers

Users label

Write Protect

Clamping hole

Index hole

Head slot

Fig 5.1 Floppy Disk


50/63

50

Adv antages of f loppy d isks are:

They are very cheap compared with other storage

They greatly enhance the on-line storage capacity

They are also convenient off-line storage medium

The floppy disks generally available in market are of 3, 5 or 8-inch

diameter size.

5.4 Uninterrupted Power Supply (UPS)

An Uninterrupted Power Supply is a device that sits between a power supply (e.g. a

wall outlet) and a device (e.g. a computer) to prevent undesired features of the power

source (outages, sags, surges, bad harmonics, etc.) from the supply from adverselyaffecting the performance of the device.

A UPS traditionally can perform the following functions:

Absorb relatively small power surges.

Smooth out noisy power sources.

Continue to provide power to equipment during line sags.

Provide power for some time after a blackout has occurred.

In addition, some UPS or UPS/software combinations provide the following

functions:

Automatic shutdown of equipment during long power outages.

Monitoring and logging of the status of the power supply.

Display the Voltage/Current draw of the equipment.

Restart equipment after a long power outage.

Display the voltage currently on the line.

Provide alarms on certain error conditions.

Provide short circuit protection.


51/63

51

There are two basic types of UPS in modern use. The first, known as 'Off-line',

passes through incoming mains power to the output sockets while the supply is good. It

monitors the line constantly for a major voltage drop that signifies power failure. It then

switches on it's inverter (the part that produces output alternating current from it's battery)

and supplies output power until the mains voltage has been restored and is stable for a

period of time. There is by definition a momentary power loss during switchover, but

typically of around five milliseconds, which is insignificant to most loads. According to

how much you pay for your UPS, you may get some conditioning of the mains power

that is passed through under normal conditions, and you may get a genuine sine-wave

output as opposed to the square-wave or trapezoidal wave that you will find on the

cheaper products.

The second type is known as an 'On-line' design because it's inverter is 'on-line'

permanently. In this design, all the incoming power is always converted to direct current,which both tops up the batteries and feeds the inverter. The inverter is constantly

producing fresh alternating current to supply the load. When the mains goes off, the

batteries are still holding up the incoming DC supply to the inverter, so the load continues

to be supplied with absolutely no break whatsoever. The inverter is a constant-duty

inverter, so this costs a little more. In any reputable on-line UPS, there is also a fail-safe

mechanism known as a 'Static Bypass' which on detecting failure in the inverter will

throw the load on the mercy of the mains supply, rather than letting it drop altogether.

This design inherently cleans the supply by virtue of reducing it to DC, then reconverting

it to fresh AC.

UPSs above 5KVA in size are almost universally on-line in design. It is difficult to

produce an on-line economically below around 600VA, so most UPSs below this size

are off-line.

Better UPSs of both designs will crop high incoming voltages and step-up low

incoming voltages without resorting to battery. When these are off-line units they are

called 'line-interactive' devices - they are nonetheless fundamentally off-line devices.

Almost all UPSs in their standard form will provide between five and ten minutessupply at full load. As a very rough estimate you can say that they will usually supply ten

to twenty minutes supply at half load. Some UPS have a facility for extended batteries.

Most on-line do, most off-line don't, but that's very general and you'll find both which

can support extended batteries. When considering UPS that support extra batteries, look


52/63

52

for extension battery cabinets that incorporate battery chargers, otherwise you get a small

charger that can't cope properly with a vast battery bank.

At a certain point, depending on manufacturer and size, you'll find it becomes more

cost-effective to revert to a 10-minute UPS and a generator fitted with mains-failure

autostart. This then gives you an effectively unlimited run time.

5.5 CHECK YOUR PROGRESS

1. The primary storage unit has:

a) Faster access time

b) Smaller storage capacity

c) Higher cost per bit of storage

d) All the above

2. The performance of the CPU may be increased by providing a small memory known

as:

a) speed buffer

b) cache memory

c) both and b

d) neither a and b

3. The disadvantage of magnetic tape as secondary storage device is :

a) no direct access to data

b) no direct verification of data

c) dirty atmosphere affects the tape recording errors

d) all the above

4. Pick up the hard disk from the following:

a) magnetic disk

b) magnetic tape

c) punched paper tape

d) all the above

5. Pick up the incorrect statement from the following magnetic disk is advantages

compared to magnetic tape:

a) Less vulnerable to damage from dust.

b) Higher transfer rate of data


53/63

53

c) Sequential processing is faster

d) None of the above

State whether the fol low ing statements are correct :

1. The amount of data that can be stored in the storage unit is called the storage

capacity.

2. The small storage areas in the storage are called location.

3. Primary storage is generally refereed to as RAM

4. The information stored inside a ROM gets lost when the power supply is switched off

5. In sequential access device, access time for all locations is same

6. Magnetic disk and magnetic drum are typical sequential access storage devices

7. Magnetic tape is the most suitable storage media for random access secondary storage

8. Floppy disks are popular external storage media used with small computers

9. Each character is represented on a column by a set of holes punched in various rows

10.Winchester disks are permanently housed in sealed, contamination-free containers.

Answers :

I 1(a) 2(c) 3(d) 4(a) 5(c)

II 1)True 2)True 3)True 4)False 5)False

6)False 7)False 8)True 9)True 10)True


54/63

54

Chapter 6

NETWORKS AND MULTIMEDIASTRUCTURE

6.0Introduction

6.1Objectives

6.2Local Area Network (LAN)

6.3Multimedia

6.4Client Server Paradigm6.5Modem

6.6Check your progress

6.0 Introduction

This deals with communication between different computers .Computer networking

(connecting computers) allows for sharing of resources such as data and peripheral

devices. Several topologies of computer networks is also presented.

In a networked computer system, with programs distributed a model called

client/server model provided for a convenient way for programs to interact. The client

/server paradigm of the different servers is also examined.

Communication device that permits connection of digital data to an existing

telephone line is referred to as MODEM.

6.1 Objectives

To understand how resources (data and peripherals ) can be shared by

networking

To understand how different services can be provided through client/server

approach

To show how the digital and the analog worlds can be bridged through

MODEM

How multimedia kit adds multimedia capabilities to a compute


55/63

55

6.2 LOCAL AREA NETWORK (LAN)

LAN is a group of computers and associated devices that share a common

communications line and typically show the resources of a single processor or server

within a small geographic are (for example, within an office building), Usually, the serverhas applications and data storage that are shared in common by multiple computer users.

A local area network may serve as few as two or three users ( for example, in a home

network) or many as thousands of users ( for example, in an FEEI network).

If you have two or more people that routinely need to easily share information and

resources you are a candidate to install a LAN, Although LANs add a level of

complexity to an office computer environment, the payback in productivity can make it

well worth the effort.

Simply put, a LAN allows you to share resources, Instead of attaching a printer toeach machine in your office, across a LAN you can share a single printer, Files that

everyone in the office needs to access frequently can be kept on the central disk drive,

and a backup routine can be implemented to ensure that these central files can be

retrieved in case of trouble, with the appropriate software, a single internet connection

can be shared by all machines on the LAN to gain access to email and the Web, LANs

can reduce the amount of money you spend on extra equipment and associated costs, and

can help improve the way people in your office use and share information.

Ne

comps ys book

Documents