computer basics

Basics of Computers

Prof. K.Adisesha, BE, MSc., M.Tech, Net

Definition of Computer?

The term computer is derived from the word compute. The word compute means to calculate. A computer is an electronic machine that accepts data from the user, processes the data by performing

calculations and operations on it, and generates the desired output results. Computer performs both simple and complex operations, with speed and accuracy.

Computers Simplified

For beginning computer users, the computer aisles at an electronics store can be quite a mystery, not to

mention overwhelming. However, computers really aren't that mysterious. All types of computers consist of two basic parts:

Hardware is any part of your computer that has a physical structure, such as the computer monitor or keyboard.

Software is any set of instructions that tells the hardware what to do. It is what guides the hardware and tells it how to accomplish each task. Some examples of software are web

browsers, games, and word processors such as Microsoft Word.

Classification of Computers

Digital and analog computers

A digital computer uses distinct values to represent the data internally. All information are

represented using the digits 0s and 1s. The computers that we use at our homes and offices are digital computers.

Analog computer is another kind of a computer that represents data as variable across a continuous range of values. The earliest computers were analog computers. Analog computers are used for

measuring of parameters that vary continuously in real time, such as temperature, pressure and voltage. Analog computers may be more flexible but generally less precise than digital computers. Slide rule is an example of an analog computer.

Characteristics of computer—

Speed, Accuracy

Diligence storage capability versatility

A brief overview of these characteristics is—

Speed The computer can process data very fast, at the rate of millions of instructions per second. Some calculations that would have taken hours and days to complete otherwise, can be completed in a few seconds using the computer. For example, calculation and generation of salary slips of

thousands of employees of an organization, weather forecasting that requires analysis of a large amount of data related to temperature, pressure and humidity of various places, etc.

Accuracy Computer provides a high degree of accuracy. For example, the computer can accurately give the result of division of any two numbers up to 10 decimal places.

Basics of Computers


Diligence When used for a longer period of time, the computer does not get tired or fatigued. It can perform long and complex calculations with the same speed and accuracy from the start till the end.

Storage Capability Large volumes of data and information can be stored in the computer and also retrieved whenever required. A limited amount of data can be stored, temporarily, in the primary

memory. Secondary storage devices like floppy disk and compact disk can store a large amount of data permanently.

Versatility Computer is versatile in nature. It can perform different types of tasks with the same ease. At one moment you can use the computer to prepare a letter document and in the next moment

you may play music or print a document.

Computers have several limitations too. Computer can only perform tasks that it has been programmed

to do. Computer cannot do any work without instructions from the user. It executes instructions as specified by the user and does not take its own decisions.

History of computer

Calculating machines, Napier‘s bones, slide rule, Pascal‘s adding and subtraction machine, Leibniz‘s multiplication and dividing machine, punch card system, Babbage‘s analytical engine, Hollerith‘s punched card tabulating machine

The key developments that took place till the first computer was developed are as follows—

Calculating Machines ABACUS was the first mechanical calculating device for counting of large numbers. The word ABACUS means calculating board. It consists of bars in horizontal positions

on which sets of beads are inserted. The horizontal bars have 10 beads each, representing units, tens, hundreds, etc.

Napier’s Bones was a mechanical device built for the purpose of multiplication in 1617 AD. by an English mathematician John Napier.

Slide Rule was developed by an English mathematician Edmund Gunter in the 16th century. Using

the slide rule, one could perform operations like addition, subtraction, multiplication and division. It was used extensively till late 1970s.

Pascal’s Adding and Subtraction Machine was developed by Blaise Pascal. It could add and subtract. The machine consisted of wheels, gears and cylinders.

Leibniz’s Multiplication and Dividing Machine was a mechanical device that could both multiply and divide. The German philosopher and mathematician Gottfried Leibniz built it around 1673.

Punch Card System was developed by Jacquard to control the power loom in 1801. He invented the punched card reader that could recognize the presence of hole in the punched card as binary

one and the absence of the hole as binary zero. The 0s and 1s are the basis of the modern digital computer.

Babbage’s Analytical Engine An English man Charles Babbage built a mechanical machine to do

complex mathematical calculations, in the year 1823. The machine was called as difference engine. Later, Charles Babbage and Lady Ada Lovelace developed a general-purpose calculating

machine, the analytical engine. Charles Babbage is also called the father of computer.

Hollerith’s Punched Card Tabulating Machine was invented by Herman Hollerith. The machine

could read the information from a punched card and process it electronically.

Basics of Computers


The developments discussed above and several others not discussed here, resulted in the development of the first computer in the 1940s.

Generations of computer

o First generation (1940 to 1956): Using vacuum tubes o Second generation (1956 to 1963): Using transistors

o Third generation (1964 to 1971): Using integrated circuits o Fourth generation (1971 to present): Using microprocessors o Fifth generation (present and next): Using artificial intelligence

The computer has evolved from a large-sized simple calculating machine to a smaller but much more powerful machine. The evolution of computer to the current state is defined in terms of the generations of computer. Each generation of computer is designed based on a new technological development,

resulting in better, cheaper and smaller computers that are more powerful, faster and efficient than their predecessors. Currently, there are five generations of computer. In the following subsections, we will

discuss the generations of computer in terms of—

i. The technology used by them (hardware and software), ii. Computing characteristics (speed, i.e., number of instructions executed per second), iii. Physical appearance, and

iv. Their applications.

First Generation (1940 to 1956): Using Vacuum Tubes

Hardware Technology The first generation of computers used vacuum tubes for circuitry and magnetic drums for memory. The input to the computer was through punched cards and paper

tapes. The output was displayed as printouts. Software Technology The instructions were written in machine language. Machine language

uses 0s and 1s for coding of the instructions. The first generation computers could solve one

problem at a time. Computing Characteristics The computation time was in milliseconds.

Physical Appearance These computers were enormous in size and required a large room for installation.

Application They were used for scientific applications as they were the fastest computing

device of their time. Examples UNIVersal Automatic Computer (UNIVAC), Electronic Numerical Integrator And

Calculator (ENIAC), and Electronic Discrete Variable Automatic Computer (EDVAC).

The first generation computers used a large number of vacuum tubes and thus generated a lot of heat. They consumed a great deal of electricity and were expensive to operate. The machines were prone to

frequent malfunctioning and required constant maintenance. Since first generation computers used machine language, they were difficult to program.

Second Generation (1956 to 1963): Using Transistors

Hardware Technology: Transistors replaced the vacuum tubes of the first generation of computers. Transistors allowed computers to become smaller, faster, cheaper, energy efficient

Basics of Computers


and reliable. The second generation computers used magnetic core technology for primary memory. They used magnetic tapes and magnetic disks for secondary storage. The input was

still through punched cards and the output using printouts. They used the concept of a stored program, where instructions were stored in the memory of computer.

Software Technology: the instructions were written using the assembly language. Assembly language uses mnemonics like ADD for addition and SUB for subtraction for coding of the instructions. It is easier to write instructions in assembly language, as compared to writing

instructions in machine language. High-level programming languages, such as early versions of COBOL and FORTRAN were also developed during this period.

Computing Characteristics: The computation time was in microseconds. Physical Appearance: Transistors are smaller in size compared to vacuum tubes, thus, the size

of the computer was also reduced.

Application: The cost of commercial production of these computers was very high, though less than the first generation computers. The transistors had to be assembled manually in second

generation computers. Examples PDP-8, IBM 1401 and CDC 1604.

Second generation computers generated a lot of heat but much less than the first generation computers. They required less maintenance than the first generation computers.

Third Generation (1964 to 1971): Using Integrated Circuits

Hardware Technology: The third generation computers used the Integrated Circuit (IC) chips. In an IC chip, multiple transistors are placed on a silicon chip. Silicon is a type of semiconductor. The use of IC chip increased the speed and the efficiency of computer,

manifold. The keyboard and monitor were used to interact with the third generation computer, instead of the punched card and printouts.

Software Technology: The keyboard and the monitor were interfaced through the operating system. Operating system allowed different applications to run at the same time. High-level languages were used extensively for programming, instead of machine language and assembly

language. Computing Characteristics: The computation time was in nanoseconds.

Physical Appearance: The size of these computers was quite small compared to the second generation computers.

Application: Computers became accessible to mass audience. Computers were produced

commercially, and were smaller and cheaper than their predecessors. Examples: IBM 370, PDP 11.

The third generation computers used less power and generated less heat than the second generation

computers. The cost of the computer reduced significantly, as individual components of the computer were not required to be assembled manually. The maintenance cost of the computers was also less compared to their predecessors.

Fourth Generation (1971 to present): Using Microprocessors

Hardware Technology They use the Large Scale Integration (LSI) and the Very Large Scale Integration (VLSI) technology. Thousands of transistors are integrated on a small silicon chip

Basics of Computers


using LSI technology. VLSI allows hundreds of thousands of components to be integrated in a small chip. This era is marked by the development of microprocessor. Microprocessor is a chip

containing millions of transistors and components, and, designed using LSI and VLSI technology. This generation of computers gave rise to Personal Computer (PC). Semiconductor

memory replaced the earlier magnetic core memory, resulting in fast random access to memory. Secondary storage device like magnetic disks became smaller in physical size and larger in capacity. The linking of computers is another key development of this era. The computers were

linked to form networks that led to the emergence of the Internet. This generation also saw the development of pointing devices like mouse, and handheld devices.

Software Technology Several new operating systems like the MS-DOS and MS-Windows developed during this time. This generation of computers supported Graphical User Interface (GUI). GUI is a user-friendly interface that allows user to interact with the computer via menus

and icons. High-level programming languages are used for the writing of programs. Computing Characteristics The computation time is in picoseconds.

Physical Appearance They are smaller than the computers of the previous generation. Some can even fit into the palm of the hand.

Application They became widely available for commercial purposes. Personal computers

became available to the home user. Examples The Intel 4004 chip was the first microprocessor. The components of the computer

like Central Processing Unit (CPU) and memory were located on a single chip. In 1981, IBM introduced the first computer for home use. In 1984, Apple introduced the Macintosh.

The microprocessor has resulted in the fourth generation computers being smaller and cheaper than their predecessors. The fourth generation computers are also portable and more reliable. They generate

much lesser heat and require less maintenance compared to their predecessors. GUI and pointing devices facilitate easy use and learning on the computer. Networking has resulted in resource sharing

and communication among different computers.

Fifth Generation (Present and Next): Using Artificial Intelligence

The goal of fifth generation computing is to develop computers that are capable of learning and self-organization. The fifth generation computers use Super Large Scale Integrated (SLSI) chips that are

able to store millions of components on a single chip. These computers have large memory requirements.

This generation of computers uses parallel processing that allows several instructions to be executed in parallel, instead of serial execution. Parallel processing results in faster processing speed. The Intel

dual-core microprocessor uses parallel processing.

The fifth generation computers are based on Artificial Intelligence (AI). They try to simulate the human way of thinking and reasoning. Artificial Intelligence includes areas like Expert System (ES), Natural

Language Processing (NLP), speech recognition, voice recognition, robotics, etc.

Classification of computer—

Basics of Computers


Microcomputers (desktop computer or Personal Computer (PC), notebook computers or laptop, netbook, tablet computer, handheld computer or Personal Digital Assistant (PDA), smart phones),

minicomputers, mainframe computers, supercomputers

The digital computers that are available nowadays vary in their sizes and types. The computers are broadly classified into four categories (Figure 1.8) based on their size and type—(1) Microcomputers, (2) Minicomputers, (3) Mainframe computers, and (4) Supercomputer.

Classification of computers based on size and type

Microcomputers

Microcomputers are small, low-cost and single-user digital computer. They consist of CPU, input unit, output unit, storage unit and the software. Although microcomputers are stand-alone machines,

they can be connected together to create a network of computers that can serve more than one user. IBM PC based on Pentium microprocessor and Apple Macintosh are some examples of

microcomputers. Microcomputers include desktop computers, notebook computers or laptop, tablet computer, handheld computer, smart phones and netbook.

Minicomputers

Minicomputers are digital computers, generally used in multi-user systems. They have high processing speed and high storage capacity than the microcomputers. Minicomputers can support 4–200 users simultaneously. The users can access the minicomputer through their PCs or terminal.

They are used for real-time applications in industries, research centers, etc. PDP 11, IBM (8000 series) are some of the widely used minicomputers.

Mainframe Computers

Mainframe computers are multi-user, multi-programming and high performance computers. They operate at a very high speed, have very large storage capacity and can handle the workload of many

users. Mainframe computers are large and powerful systems generally used in centralized databases. The user accesses the mainframe computer via a terminal that may be a dumb terminal, an intelligent terminal or a PC. A dumb terminal cannot store data or do processing of its own. It

has the input and output device only. An intelligent terminal has the input and output device, can do processing, but, cannot store data of its own. The dumb and the intelligent terminal use the

processing power and the storage facility of the mainframe computer. Mainframe computers are

Basics of Computers


used in organizations like banks or companies, where many people require frequent access to the same data. Some examples of mainframes are CDC 6600 and IBM ES000 series.

Supercomputers

Supercomputers are the fastest and the most expensive machines. They have high processing speed compared to other computers. The speed of a supercomputer is generally measured in FLOPS

(Floating point Operations Per Second). Some of the faster supercomputers can perform trillions of calculations per second. Supercomputers are built by interconnecting thousands of processors that

can work in parallel.

Supercomputers are used for highly calculation-intensive tasks, such as, weather forecasting,

climate research (global warming), molecular research, biological research, nuclear research and aircraft design. They are also used in major universities, military agencies and scientific research

laboratories. Some examples of supercomputers are IBM Roadrunner, IBM Blue gene and Intel ASCI red. PARAM is a series of supercomputer assembled in India by C-DAC (Center for Development of Advanced Computing), in Pune. PARAM Padma is the latest machine in this

series. The peak computing power of PARAM Padma is 1 Tera FLOP (TFLOP).

The Computer System

Computer is an electronic device that accepts data as input, processes the input data by performing

mathematical and logical operations on it, and gives the desired output. The computer system consists of four parts—(1) Hardware, (2) Software, (3) Data, and (4) Users.

Hardware consists of the mechanical parts that make up the computer as a machine. The hardware consists of physical devices of the computer. The devices are required for input, output, storage and

processing of the data. Keyboard, monitor, hard disk drive, floppy disk drive, printer, processor and motherboard are some of the hardware devices.

Software is a set of instructions that tells the computer about the tasks to be performed and how these tasks are to be performed. Program is a set of instructions, written in a language understood by the computer, to perform a specific task. A set of programs and documents are collectively

called software. The hardware of the computer system cannot perform any task on its own. The hardware needs to be instructed about the task to be performed. Software instructs the computer

about the task to be performed. The hardware carries out these tasks. Different software can be loaded on the same hardware to perform different kinds of tasks.

Data are isolated values or raw facts, which by themselves have no much significance. For example, the data like 29, January, and 1994 just represent values. The data is provided as input to

the computer, which is processed to generate some meaningful information. For example, 29, January and 1994 are processed by the computer to give the date of birth of a person.

Users are people who write computer programs or interact with the computer. They are also known as skinware, liveware, humanware or peopleware. Programmers, data entry operators, system analyst and computer hardware engineers fall into this category.

The Input-Process-Output Concept

Basics of Computers


A computer is an electronic device that (1) accepts data, (2) processes data, (3) generates output, and (4) stores data. The concept of generating output information from the input data is also

referred to as input-process-output concept.

The input-process-output concept of the computer is explained as follows—

Input The computer accepts input data from the user via an input device like keyboard. The

input data can be characters, word, text, sound, images, document, etc.

Process The computer processes the input data. For this, it performs some actions on the data

by using the instructions or program given by the user of the data. The action could be an arithmetic or logic calculation, editing, modifying a document, etc. During processing, the data,

instructions and the output are stored temporarily in the computer‘s main memory.

Output The output is the result generated after the processing of data. The output may be in the

form of text, sound, image, document, etc. The computer may display the output on a monitor, send output to the printer for printing, play the output, etc.

Storage The input data, instructions and output are stored permanently in the secondary storage devices like disk or tape. The stored data can be retrieved later, whenever needed.

Components of Computer Hardware

The computer system hardware comprises of three main components —

1. Input/output (I/O) Unit,

2. Central Processing Unit (CPU), and 3. Memory Unit.

The I/O unit consists of the input unit and the output unit. CPU performs calculations and processing on the input data, to generate the output. The memory unit is used to store the data, the instructions and the output information. Figure illustrates the typical interaction among the

different components of the computer.

The computer system interaction

Basics of Computers


Input/Output Unit The user interacts with the computer via the I/O unit. The Input unit accepts data from the user and the Output unit provides the processed data i.e. the information to the

user. The Input unit converts the data that it accepts from the user, into a form that is understandable by the computer. Similarly, the Output unit provides the output in a form that is

understandable by the user. The input is provided to the computer using input devices like keyboard, trackball and mouse. Some of the commonly used output devices are monitor and printer.

Central Processing Unit CPU controls, coordinates and supervises the operations of the

computer. It is responsible for processing of the input data. CPU consists of Arithmetic Logic Unit (ALU) and Control Unit (CU).

o ALU performs all the arithmetic and logic operations on the input data. o CU controls the overall operations of the computer i.e. it checks the sequence of

execution of instructions, and, controls and coordinates the overall functioning of the

units of computer. Additionally, CPU also has a set of registers for temporary storage of data, instructions, addresses

and intermediate results of calculation.

Memory Unit Memory unit stores the data, instructions, intermediate results and output,

temporarily, during the processing of data. This memory is also called the main memory or primary memory of the computer. The input data that is to be processed is brought into the main

memory before processing. The instructions required for processing of data and any intermediate results are also stored in the main memory. The output is stored in memory before being transferred to the output device. CPU can work with the information stored in the main

memory. Another kind of storage unit is also referred to as the secondary memory of the computer. The data, the programs and the output are stored permanently in the storage unit of

the computer. Magnetic disks, optical disks and magnetic tapes are examples of secondary memory.

Application of Computers

Application of computers—Education, entertainment, sports, advertising, medicine, science and

engineering, government, home

Computers have proliferated into various areas of our lives. For a user, computer is a tool that provides the desired information, whenever needed. You may use computer to get information about the reservation of tickets (railways, airplanes and cinema halls), books in a library, medical history of a

person, a place in a map, or the dictionary meaning of a word. The information may be presented to you in the form of text, images, video clips, etc.

Storage Devices

Primary Storage Devices

Different types of primary storage devices are:

RAM

ROM

Basics of Computers


Random Access Memory (RAM) is the best known form of Computer Memory. The Read and write (R/W) memory of a computer is called RAM. The User can write information to it and read information

from it.With RAM any location can be reached in a fixed ( and short) amount of time after specifying its address.

The RAM is a Volatile memory, it means information written to it can be accessed as long as power is on. As soon as the power is off, it cannot be accessed. so this mean RAM computer memory essentially

empty. RAM holds data and processing instructions temporarily until the CPU needs it.

RAM is considered ―random access‖ because you can access any memory cell directly if you know the

row and column that intersect at that cell. RAM is made in electronic chips made of so called semiconductor material, just like processors and many other types of chips. In RAM, transistors make

up the individual storage cells which can each ―remember‖ an amount of data, for example, 1 or 4 bits – as long as the PC is switched on. Physically, RAM consists of small electronic chips which are mounted in modules (small printed circuit boards). The modules are installed in the PC‘s motherboard

using sockets – there are typically 2, 3 or 4 of these.

There are two basic types of RAM :

(i) Dynamic Ram

(ii) Static RAM

Dynamic RAM: loses its stored information in a very short time (for milli sec.) even when power supply is on. D-RAM‘s are cheaper & lower.

Similar to a microprocessor chip is an Integrated Circuit (IC) made of millions of transistors and capacitors.

In the most common form of computer memory, Dynamic Memory Cell, represents a single bit of data. The capacitor holds the bit of information – a 0 or a 1. The transistor acts as a switch that lets the

control circuitry on the memory chip read the capacitor or change its state. A capacitor is like a small bucket that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons.

To store a 0, it is emptied. The problem with the capacitor‘s bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the

CPU or the Memory Controller has to come along and recharge all of the capacitors holding it before they discharge. To do this, the memory controller reads the memory and then writes it right back. This

refresh operation happens automatically thousands of times per second.

This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically

refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory.

Static RAM uses a completely different technology. S-RAM retains stored information only as long as the power supply is on. Static RAM‘s are costlier and consume more power. They have higher speed

than D-RAMs. They store information in Hip-Hope.

In static RAM, a form of flipflop holds each bit of memory. A flip-flop for a memory cell takes four or

six transistors along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic RAM. However, because it has more parts, a static memory cell takes

Basics of Computers


up a lot more space on a chip than a dynamic memory cell. Therefore, you get less memory per chip, and that makes static RAM a lot more expensive. Static RAM is fast and expensive, and dynamic RAM

is less expensive and slower. Static RAM is used to create the CPU‘s speedsensitive cache, while dynamic RAM forms the larger system RAM space.

Some other RAMS are :

(a) EDO (Extended Data Output) RAM : In an EDO RAMs, any memory location can be accessed. Stores 256 bytes of data information into latches. The latches hold next 256 bytes of information so that in most programs, which are sequentially executed, the data are available without wait states.

(b) SDRAM (Synchronous DRAMS), SGRAMs (Synchronous Graphic RAMs) These RAM chips use

the same clock rate as CPUuses. They transfer data when the CPU expects them to be ready.

(c) DDR-SDRAM (Double Data Rate – SDRAM) : This RAM transfers data on both edges of the

clock. Therefore the transfer rate of the data becomes doubles.

ROM : Read only memory: Its non-volatile memory, ie, the information stored in it, is not lost even if

the power supply goes off. It‘s used for the permanent storage of information. It also posses random access property. Information cannot be written into a ROM by the users/programmers. In other words

the contents of ROMs are decided by the manufactures.

The following types of ROMs an listed below:

(i) PROM : It‘s programmable ROM. Its contents are decided by the user. The user can store

permanent programs, data etc in a PROM. The data is fed into it using a PROM programs.

(ii) EPROM : An EPROM is an erasable PROM. The stored data in EPROM‘s can be erased by

exposing it to UV light for about 20 min. It‘s not easy to erase it because the EPROM IC has to be removed from the computer and exposed to UV light. The entire data is erased and not selected portions by the user. EPROM‘s are cheap and reliable.

(iii) EEPROM (Electrically Erasable PROM) : The chip can be erased & reprogrammed on the board

easily byte by byte. It can be erased within a few milliseconds. There is a limit on the number of times the EEPROM‘s can be reprogrammed, i.e.; usually around 10,000 times.

Flash Memory: It is an electrically erasable & programmable permanent type memory. It uses one transistor memory all resulting in high packing density, low power consumption, lower cost & higher reliability. It is used in all power, digital cameras, MP3 players etc.

Secondary Storage Devices

Secondary storage devices are also called backup storage because it is used to store data. Volume of data on permanent basis which can be partially transferred to the primary storage, when required for

data processing. Afterwards these devices are comparatively cheap and provide greater space to store the data /instructions are stored on secondary storage devices in the same binary codes as in primary

storage. Needs of Secondary Storage Device

Basics of Computers


The storage capacity of the primary storage of today‘s computer is not sufficient. To store a large volume of data as a result additional memory called secondary storage is needed with most of the

computer system.

These devices also provide the fast communication than I/O devices. The internal memory of a computer is a volatile memory. Therefore, we cannot save the data permanently. In that case we require secondary storage device which provide the facility to store the data for future use.

Floppy Disk

A floppy disk, also called simply a diskette or disk, is a small flexible Mylar disk coated with iron oxide on which data are stored. The floppy disk has been around since early 1970s, today it is available

in three 3½ inch, 5¼ inch and 8 inch sizes. The 5¼ and 8 inch diskettes are covered by stiff protective jacket with different holes. The central big hole called hub ring which is used to hold by disk drive

during rotation. The elongated read write window is used to read and write data through read/write head. The small hole next to the hub ring is called index hole which is used to locating data through computer. The cut out on the side of the floppy disk is called write protect notch. If we cover this

opening with a piece of paper then we can‘t write data on to disk.

In small diskette a hard plastic cover and protective metal is used to protect disk. Before using a disk

we have to format a disk in which disk is divided into tracks and sectors for storing the data. Diskettes may be double sided and single sided while the storage capacity become less or more.

Floppy diskettes are more convenient to use with microcomputers. A floppy disk which is a random access device can access data fast than magnetic tape.

Magnetic Tape

Magnetic tape is a sequential access device about one half or one fourth inch in size and made of Mylar (a plastic material) coated with a thin layer of iron oxide. Data can be read and write through a device which is called tape drive. The read/write head of tape drive which is an electromagnetic component

read, write and erase data from magnetic tape. Magnetic tape is divided into nine separate strips or tracks in which eight tracks are used to store data and ninth track is used for error checking bit.

Magnetic tape can store large quantities of data therefore they are erasable, usable and durable secondary storage device. But it can use with large computers.

Disk Drive

Disk drive is a peripheral device that reads or write the disks (hard disks, floppy disks, etc) that store information. Disk drives are called ―Storage Device‖ because they store information or portabel or permanent disks. The drive contains a motor to rotate the disk at a constant rate and one or more

read/write heads, which are positioned over the desired track.

CD-Writer

A CD writer is a device connected to your computer which can write on CD-WR and CD-R discs. CD-

WR discs may be written, erased and rewritten, while CD-R discs may be written only once. CD writer performances is measured in X unit, where IX =150 kilobytes/sec. This allows user to master a CD-

ROM or audio CD for publishing CD-R devices can also read CD-ROMs and play audio CDs. The CD writer is also called a CD-R drive (short for Compact Disc – Recordable Drive)

Basics of Computers


Computer Input and Output Devices

INPUT DEVICES

Input devices are used to provide data or information to the computer. The computer follows the instructions given to it by and input device. A variety of input devices are used with the computer depending on the type and purpose of input information. For example, a keyboard is commonly used to

transfer data or information from human readable form to machine readable form. Other examples of input devices are: mouse, joystick, trackball, light pens, digitizers, scanners, optical character reader

(OCR), touch window, etc.

Mouse

The mouse is an input device that usually contains one or two buttons. As a user moves the mouse on a

flat surface, the mouse controls the cursor movement on the screen. When the user presses one of the buttons, the mouse either marks a place on the screen or makes selection from data or menu on the screen. A mouse has a sphere on its underside. This rotates as the mouse is moved along a flat surface.

The mouse translates the direction and speed of rotation into a digital signals that identifies the position or control, the cursor on the computer.

A mouse can be used for many applications, ranging from games to drawing and designing products with computer graphics. It provides an alternative for people who are uncomfortable with a keyboard

but it also can be used in combination with a keyboard to input data.

Trackball

A Trackball is a pointing device almost like a mouse turned upside down. The user controls the cursor

on the screen by rolling a plastic ball with a fingertip or wrist. To execute commands with a Trackball, one or more buttons are pressed, much in the same way as is done with a mouse. The cursor can be

moved around on the screen by rolling the ball with a thumb or finger.

Trackball is popular among users of laptop computers when space is limited and may be mounted on

either side of the keyboard. For handicapped people who may have difficulty pressing keys on a standard keyboard or using a mouse, the trackball may be the answer since it edoes not require to moves the entire arm to use it.

Scanner

Scanner is an input device. It is also called Optical Reader or Digital Scanner. It scans or reads text and picture printed on a paper and enters them directly into the computer memory.

The advantage of a scanner is that the user needs not type the input data in. This is a lust and accurate

method for entering data into the computer. The scanner takes electronic images, of text or pictures from the paper it breaks each image into light and dark dots and stores them into the computer memory in machine codes. Scanned text can be edited by OCR software. Optical Character Recognition (OCR)

software translates the scanned document into text that can be edited.

The image scanner is useful because it translates printed images into an electronic format than can be stored in computer‘s memory. The stored image can be transferred into a paint program or directly into a word processor. You can use software to organize and manipulate the electronic image.

Basics of Computers


Keyboard

A keyboard is the most commonly used input device which helps us in simply keying in required information in a computer. This information is subsequently stored in the computer‘s memory. A

keyboard can be used effectively to communicate with the computer but considered to be relatively slow as compared to other input devices. The keyboard is divided into following divisions:

o Alphabetic Keypad

These keys are similar to a standard typewriter and is used to type general information.

o Numeric Keypad

These keys are used to input numeric data only. These are very useful in case of large numeric data input because all numeric keys can be accessed by one hand only. These keys can also be used as an

alternative to the screen navigation and editing keys.

o Function Keys

These are keys marked as F1 – F12, located normally at the top of the keyboard. These are special keys

provided to a programmer which allow him to attach special functions to each key. Each of these function keys are also given some special function in different packages.

OUTPUT DEVICES

An output device is used to display the data or information that we receive from the computer. An output device can be used to display or print the intermediate or final results performed by computer. A variety of output devices are used with computer. The use of these devices depends on the type and

purpose of output. Some examples of output devices are: Monitors, Printer, Plotters, Visual display unit (VDU), liquid crystal display (LCD), etc.

MONITOR To display result or output from computer, a T.V like device is used which is called monitor. The

monitors are also referred as C.R.T (Cathode Ray Tube), V.D.U (Visual Display Unit). The monitor assist during input from the keyboard, this display is called a soft copy. The monitor can be of various kinds, depending on the type of application. Monitors are categorized into two groups:

1. Monochrome monitors

2. Colour monitors 1. Monochrome Monitors

Monochrome monitors are used specially for text editing purpose. These monitors can display only one colour. Normally amber, green or paper white.

2. Colour Monitors Colour monitors serves a wide range of selection according to the application. Such as red, green, blue,

Enhance Graphic Array (EGA), Colour Graphic Array (CGA), Video Graphics Array (VGA), Super Video Graphics Array (SVGA).

There are two types of colour monitors: i. CRT Monitor

Basics of Computers


ii. LCD Monitor

i. CRT Monitor

The CRT monitors are a lot like television set, using the same CRT or Cathorde Ray Tube technology. The CRT monitor has two major parts; the screen and the cathode ray tube (CRT). The screen is the front of the monitor and CRT is fitted inside the monitor.

ii. LCD or Flat Panel Monitor

Another monitor type is LCD or Liquid Crystal Display. LCD monitors are a lot like CRT monitors without the bulkiness but they do not have CRT. LCD monitors use a flat lightweight surface filled

with millions of tiny glass bubbles, each having a phosphoric covering. These phosphoric coverings glow to create an image. LCD screens provide clarity and flicker-free viewing.

PLOTTER Plotter is a special output device, which is used to produce high quality, perfectly proportional hard

copy output. Plotters are designed to produce large drawings or images such as construction plans for buildings or blue prints for mechanical devices. Plotters have been used in automotive and aircraft design, topological surveys, architectural layouts and other similar complex drafting jobs.

A plotter is composed of a pen, a move-able carriage, a drum and a holder for chart paper. Both the pen and the paper can move up and down and back and forth. This permits very detailed drawings. Some

plotter having coloured pens can make coloured drawings also.

There are two types of plotters, which are as follows:

1. Drum Plotter 2. Flatbed Plotter

1. Drum Plotter

On the drum plotter, the pens, and the drum move concurrently in different axes to produce the image. Drum plotters are used to produce continuous output, such as plotting earthquake activity, or for long graphic output, such as structural view of a skyscraper.

2. Flatbed Plotter

On some flatbed plotters, the pen moves in both axes while the paper remains stationary. However, on most desktop plotters, both paper and pen move concurrently in much the same way as on drum

plotters.

PRINTER

A computer peripheral that puts text or a computer generated image on paper or on another medium, such as a transparency. Printer can be categorized in several ways the most common distinction is

IMPACT and NON-IMPACT.

o Impact Printing

Is the method used by the conventional type writers. In some type of impact printing a metal ―hammer‖ embossed with a character strikes a print ribbon, which presses the characters image into paper. In other

Basics of Computers


types the hammer strikes the paper and presses it into the ribbon characters created through impact printing can be formed by either a solid font or dot matrix printing mechanism.

o Non – Impact Printing

Does not depend on the impact of metal on paper. In fact no physical contact at all occurs between the printing mechanism and the paper. The most popular non-impact methods today utilize thermal

transfer, ink-jet.

TYPES OF PRINTERS

1. Dot Matrix Printer

Any printer that produces character made up of dots using a wire pin printed head. The quality of output from a dot matrix printer depends largely on the number of dots in the matrix, which might be

low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot matrix printers are often categorized by the number of pins in the printer head typically, 9 or 24.

2. Line Printers

Any printer that prints one line at one time, as opposed to one character at a time or one page at a time. Line printer typically produces the 11 by 17 inch ―computer‖ printout. They are high speed devices and

are often used with mainframes, minicomputers, or networked machines rather than with single user system. Types of line printers include chain printers and band printer.

3. Laser Printers

An electrophotographic printer that is based on the technology used by photocopiers. A focused laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum. This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A

piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper. Finally, the electrified

charge is removed from the drum and the excess toner is collected. By omitting the final step and repeating only the toner application and paper handling steps, the printer can make multiple copies.

4. Daisy Wheel Printer

Daisy wheel printer are sometimes called letter quality printer because they are often used to produce

attractive correspondence. The D.W.P is a flat circular device made of metal with character embossed on it. As this wheel spins at a very high speed the hammer hits the specific character against the ribbon

which presses against the paper.

5. Thermal Transfer Printer

It is a kind of non-impact printer. In electrothermal printing, characters are burned on to a special paper by heated rods on a print heat. They transfer ink from a wax-based ribbon onto plain paper. This printer

can support high quality graphic.

6. Ink – Jet Printer

Basics of Computers


Voice Recognition

A voice recognition system compares a person‘s live speech to their stored voice pattern. Larger organizations sometimes use voice verification systems as time attendance devices. Many companies

also use this technology for access to sensitive files and networks. Some financial services use voice verification systems to secure telephone banking transactions. These systems use speaker dependent voice recognition software. This type of software requires the computer to make a profile of your voice,

that is, you train the computer to recognize your inflection patterns.

PERIPHERAL DEVICE

A computer device, such as a CD-ROM drive or printer, which is not part of the essential computer,

i.e., the memory and microprocessor. Peripheral devices can be external -- such as a mouse, keyboard, printer, monitor, external Zip drive or scanner -- or internal, such as a CD-ROM drive, CD-R drive or

internal modem. Internal peripheral devices are often referred to as integrated peripherals. Linkage between the CPU and the users is provided by Peripheral devices.

Network Interface Card (NIC)

Any computer that is to be connected to a network, needs to have a network interface card (NIC).

Most modern computers have these devices built into the motherboard, but in some computers you

have to add an extra expansion card (small circuit board)

Some computers, such as laptops, have two NICs: one for wired connections, and one for wireless

connections (which uses radio signals instead of wires)

In a laptop, the wireless radio antenna is usually built in to the side of the screen, so you don't need to have a long bit of plastic sticking out the side of your computer!

Network Cable

To connect together different devices to make up a network, you need cables.

Cables are still used in most networks, rather than using only wireless, because they can carry much

more data per second, and are more secure (less open to hacking).

Basics of Computers


The most common type of network cable cable in use today looks like the one shown above, with plastic plugs on the ends that snap into sockets on the network devices.

Inside the cable are several copper wires (some used for sending data in one direction, and some for the other direction).

Hub

A hub is a device that connects a number of computers together to make a LAN. The typical use of a hub is at the centre of a star network (or as part of a hybrid network) - the hub has

cables plugged into it from each computer.

A hub is a ‗dumb‘ device: if it receives a message, it sends it to every computer on the network. This

means that hub-based networks are not very secure - everyone can listen in to communications.

Hubs are pretty much obsolete now (you can't buy them any more), having been superseded by cheap switches.

Switch

A switch, like a hub, is a device that connects a number of computers together to make a LAN. The typical use of a switch is at the centre of a star network (or as part of a hybrid network) - the switch has cables plugged into it from each computer.

A switch is a more ‗intelligent‘ device than a hub: if it receives a message, it checks who it is addressed to, and only sends it to that specific computer. Because of this, networks that use switches are more

secure than those that use hubs, but also a little more expensive.

Router

A router is a network device that connects together two or more networks. A common use of a router is to join a home or business network (LAN) to the Internet (WAN).

The router will typically have the Internet cable plugged into it, as well as a cable, or cables to computers on the LAN.

Basics of Computers


Alternatively, the LAN connection might be wireless (WiFi), making the device a wireless router. (A wireless router is actually a router and wireless switch combined)

Routers are the devices that join together the various different networks that together make up the Internet.

These routers are much more complex than the one you might have in your home

Modem

Before the days of broadband Internet connections, most computers connected to the Internet via telephone lines (dial-up connections).

The problem with using telephone lines is that they are designed to carry voices, which are analogue signals. They are not designed for digital data.

The solution was to use a special device to join the digital computer to the analogue telephone line. This device is known as a modem.

A modem contains a DAC and an ADC.

The DAC in the modem is required so that the digital computer can send data down the analogue telephone line (it converts digital data into noises which is exactly what the telephone line is designed to carry.)

The ADC in the modem is required so that the analogue signals (noises) that arrive via the telephone line can be converted back into digital data.

The reason telephone lines were used is that almost every building in the world is already joined to every other via the telephone system.

Basics of Computers


Using the telephone system for connecting computers meant that people didn‘t have to install new wires to their houses and offices just for computer use.

In the last few years however, this is exactly what people have done. Special cables have been installed just for Internet access.

These special cables are designed to carry digital data, so no modem is required. The word modem is an abbreviation of MOdulator DEModulator. A modulator acts as a DAC, and a demodulator acts as an ADC.

So, simply put, a modem is required because computers are digital devices and the telephone system is

analogue. The modem converts from digital to analogue and from analogue to digital.

Types of Software

There are two categories of software:

Systems Software - These are the programs that enable the computer to work effectively and

provide an interface for the user to interact with the computer.

Applications Software - These programs all enable the user to perform a range of tasks. It is

these programs that people use computers for.

We will look closely at Systems Software to start with.

Operating Systems

The operating system (OS) is the first program that loads when your computer is switched on and the last one to be unloaded when you switch off. It controls all the hardware and enables the user to

actually use the computer. There are a number of different operating systems available for computers.

Windows - Microsoft's operating system is the most common operating system.

MacOS - The operating system for Apple Mac's.

UNIX - The operating system of many business computers & mainframes.

Linux - A free operating system developed originally by Linus Torvalds as a project and is now built upon and improved by programmers for free.

The OS provides software with a standard way of communicating with the different hardware devices. If an application needs to save a file or print, it is the operating system which deals with the task. If

there was no OS then each application would need to have its own way of communicating with the hardware. This would be a difficult task as there are many different hardware setups (different printers, hard discs etc) and the application must be able to cope with all of them. In addition it would make

transfering data between applications very difficult.

The operating system has a number of functions which are critical to the workings of a computer.

Memory Allocation

Basics of Computers


The OS manages memory (RAM). When applications are loaded they need memory to work with. The OS allocates software RAM to work in. It needs to make sure that the RAM allocated is not used by

another application. This task is becoming more critical as computers are often multitasking (ie doing more than one task at once).

The OS also manages virtual memory. In this way the computer can run more applications than it has RAM for. For example if a computer was running a word processor and the user wanted to load a

spreadsheet application at the same time, it would be a simple task if the computer had adequate RAM to have both apps in memory at once. If there was not enough RAM then the OS would use the hard

disc as virtual RAM. It would take some or all of the wordprocessor from RAM (including any documents that were been editted) and store then on the hard disc before loading the spreadsheet app. When the user switched back to the word processor, then the spreadsheet program would be saved to

the hard disc while the while the word processor would be loaded, documents as well, carrying on from where the user left off.

Interupt Handling

When the various hardware components such as mouse, keyboard or modem need to communicate with the processor (when a mouse is clicked or when a key is pressed) an interupt signal is generated. This interrupt needs to be dealt with immediately, so the OS needs to handle both the interrupt and whatever

processes which were currently being done.

Storage

It is the OS which organises the storage and retrieval of data to hard and floppy discs. It is the OS

which determines what is an acceptable file or directory name. The OS must be able to swiftly locate files and uses a directory to do this. When an application needs to save a file it is passed onto the OS which deals with the transfer to disc.

Communication with Hardware Devices

The operating system needs to communicate with the various hardware components which make up the computer. Special programs called drivers enable the OS to communicate with these hardware devices.

Drivers are needed as the hardware which makes up a PC may be vastly different to that of another PC with the same OS installed. As the components are often made by different companies the internal workings will be different to each other. Drivers are translation programs which convert the messages

from the OS into messages that the hardware device can understand.

Other Systems Software

There are other pieces of software which come under the category of Systems Software.

Utility Software

Scan Disc - Hard discs and floppy discs can develop errors, both in their filing systems and the physical disc itself. Scan disc software checks the discs for errors. If there are file system errors

it trys to fix them. If there is an error with the disc itself the file system is updated so that so that files are not saved to that part of the disc.

Defragment - When files are deleted and new files created, the OS just saves them where it can. Sometimes the OS will begin saving a file in a part of the hard disc which is free, without

Basics of Computers


checking first if there is enough space. So the OS has to split the file, and save the rest in another part of the disc. This can slow the retrieval of the file from disc at a later date.

Defragment puts all the parts of files together and puts all the empty sectors of the disc in one place. Frequently used files are often placed at the start of the disc to improve performance.

Virus Checkers - Computers can become infected with computer viruses, small malicious programs which duplicate themselves causing havoc with files and programs. Virus checkers

scan discs and incoming files from the Internet to for viruses. When one if found the virus checker may try to disinfect the file, removing the virus, or simply delete the file, virus and all.

New viruses are released all the time so this software needs constant updating to enable the latest viruses to be caught.

Compilers & Interpreters

When computer programs are written they need to be converted into machine code. This binary code is

the language which the computer understands. A Compiler converts the program code into machine code and saves the machine code into a file which can be executed. This program can be transfered to

other PCs and used without the need for a compiler. An Interpreter works in a similar manner in that program code is converted into machine code, but is executed straight away without being stored. To run the program it needs to be interpreted every time. Most applications such as word processors are

created when program code is compiled into machine code. Macros, mini programs which can record & playback keystrokes and mouse clicks in applications like word processors or spreadsheets, are

interpreted each time they are run and so need an Interpreted.

File management software

Software can be used to manage files, compressing them or creating a partition which divides up the hard disc to create sections which the OS will recognise as two seperate drives.

Security Software

Security Software is needed to make files secure especially when dealing with a network. These utility programs control logins and file access and permissions.

Applications Software

Applications are the programs we use computers for. Programs like word processors, spreadsheets and databases are examples of applications but all applications can be grouped into one of the following

categories based on their applications.

Applications are software programs that perform specific tasks for us. You have probably used many

different types of applications. Here are some common ones:

• Activity management programs like calendars and address books

• Word processing applications for creating documents that are attractively formatted • Spreadsheet applications for creating documents to manage and organize numerical data

• Presentation applications for making slide shows • Graphics applications for creating pictures • Database applications for developing databases that can organize and retrieve large amounts of

information

Basics of Computers


• Communications programs like e-mail and faxing software for sending and receiving messages • Multimedia applications for creating video and music

• Utilities for performing a variety of tasks that maintain or enhance the computer‘s operating system. computer Network

A network is any collection of independent computers that communicate with one another over a shared network medium. A computer network is a collection of two or more connected computers.

When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected

using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct video conferences in real time with other remote users.

When a network becomes open sourced it can be managed properly with online collaboration software. As companies rely on applications like electronic mail and database management for core business operations, computer networking becomes increasingly more important.

Every network includes:

At least two computers Server or Client workstation.

Networking Interface Card's (NIC)

A connection medium, usually a wire or cable, although wireless communication between

networked computers and peripherals is also possible.

Network Operating system software, such as Microsoft Windows NT or 2000, Novell NetWare, Unix and Linux.

Types of Networks:

LANs (Local Area Networks)

A network is any collection of independent computers that communicate with one another over a shared network medium. LANs are networks usually confined to a geographic area, such as a single building or a college campus.

LANs can be small, linking as few as three computers, but often link hundreds of computers used by

thousands of people. The development of standard networking protocols and media has resulted in worldwide proliferation of LANs throughout business and educational organizations.

WANs (Wide Area Networks)

Wide area networking combines multiple LANs that are geographically separate. This is accomplished

by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services. Wide area

networking can be as simple as a modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances.

Other Types of Area Networks

While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:

Basics of Computers


Wireless Local Area Network - a LAN based on WiFi wireless network technology

Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity

such as a government body or large corporation.

Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as

on a university or local business campus.

Storage Area Network - connects servers to data storage devices through a technology like

Fiber Channel.

System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.

Internet

The Internet is a system of linked networks that are worldwide in scope and facilitate data

communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups.

http://compnetworking.about.com/cs/wireless80211/g/bldef_wifi.htm

http://compnetworking.about.com/cs/fibrechannel/g/bldef_fibrechan.htm