BASIC COMPONENTS OF COMPUTER SYSTEM

 BASIC COMPONENTS OF COMPUTER SYSTEM

Here is the representation of the basic components of any computer system:

“Basic Components of a Computer System”

2.1.2 COMPUTER SYSTEM

A system is a group of related components that make up a body to perform a specific

function. Therefore, a computer system is defined as:

“The computer along with various units and software

that perform different activities in data processing

is collectively known as computer system”

2.1.3 PARTS OF COMPUTER SYSTEM

Any computer system can be divided into two basic components:

1. Hardware Components

2. Software Components

2.1.3.1 HARDWARE COMPONENTS

Computer Hardware can be defined as:

“Electronic and mechanical devices that make up the computer

are called the hardware”

Computer hardware refers to all the physical, tangible components related to computers.

We can say that the “computer hardware” is the structural study of computers. All the

physical items like Printers, Monitors, Keyboard, Mouse, Disks, Chips and Circuits etc. are

included in the computer hardware.

“The physical and permanent components

of a computer are called hardware”

So, hardware components are the physical and tangible parts of computer system without

which computer system can not be complete.

Input/Output

Devices

CPU

Memory

System

Application

Computer System

Hardware Software

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TYPES OF HARDWARE

Hardware can be divided into three basic types:

1. Input/output devices

2. Central Processing Unit (CPU)

3. Memory

2.1.3.2 SOFTWARE COMPONENTS

“A set of electronic instructions consisting of complex codes, or

programs, that makes up the computer are called the software”

Computer software refers to the instructions to operate the hardware. We can say that

“computer software” is the functional study of computers. Computer software includes

applications and programs like Word processor, Spreadsheets, Databases, Graphical

programs, Multimedia programs etc. So, softwares are the non-physical and in-tangible

parts of computer system without which computer system can not be complete.

TYPES OF SOFTWARE

Software can be divided into two basic types:

1. System Software

2. Application Software

2.2 BASIC ARCHITECTURE OF

COMPUTER SYSTEM

The basic or internal architectural design of computer differs from one system model to

another. However the basic organization remains same for all computer systems. As shown

in the following figure of “data processing cycle”, the user inputs the data through input unit;

the data goes for processing, meanwhile or after processing results stored in memory

temporarily/permanent and then the output of results (information) goes to output unit.

Figure 2.3

“Data Processing Cycle”

2.2.1 BASIC OPERATIONS BY BASIC UNITS

These three basic units correspond to the five basic operations performed by the computer

system.

1. Input Unit

Storage

Input

Processing

Unit Output

Data Information

Input Unit Output Unit

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2. Output Unit

3. Processing Unit

i. Memory Unit

ii. Arithmetic Logic Unit

iii. Control Unit

Following is a block diagram of the organization of basic computer units; in this figure the

solid lines are used to indicate the flow of instruction and data, and the dotted lines

represent the control exercised by the control unit. It displays the five major building blocks,

or functional units of a digital computer system.

Figure 2.4

“Representation of Computer Structure”

2.2.1.1 INPUT UNIT

Input unit can be defines as:

“Unit which is used to get data from

the user to computer is called the input unit”

The input unit receives the input of data which is in need of processing. For this purpose

different input devices (i.e. keyboard, mouse etc) can be used. These devices are helpful to

make connection between the outer environment and the inner environment of the

computer. The data provided by the input devices to the computer is transformed into the

binary codes which are acceptable by the computer memory.

Following are the functions performed by the input unit:

1. It accepts (or reads) the list of instructions and data from the outside world of computer.

2. It converts these instructions and data in computer acceptable form.

3. It supplies the converted instructions and data to the computer system for further

processing.

2.2.1.2 CENTRAL PROCESSING UNIT (CPU)

Central processing unit can be defined as:

OUTPUT UNIT

Retrieved data

MEMORY from CPU

UNIT

Program and

data are stored

ARITHMETIC

LOGIC UNIT

Arithmetic and

logical

operations are

performed

CONTROL

UNIT

Directs all

operations

CENTRAL PROCESING UNIT (CPU)

INPUT UNIT

Feed data to

CPU

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“The computer‟s brain which organizes and carries out

instructions from either the user or the software”

CPU resides on a circuit board called the motherboard and can be described as the

"brains" of the computer. The control unit (CU), memory unit (MU) and the arithmetic logic

unit (ALU) of a computer system are jointly known as the “central processing unit (CPU)”.

The CPU is the brain of any computer system. In a human body, all decisions are taken by

the brain and the other parts of the body function as directed by the brain. Similarly, in a

computer system, all calculations and comparisons are made by or inside the CPU and the

CPU is also responsible for activating and controlling the operations of other units of

computer system.

FUNCTIONS OF CENTRAL PROCESSING UNIT (CPU)

CPU performs the following main functions:

1. Fetch (read) data and programme instructions

2. Decode them

3. Execute them

4. Control the flow of program and date in and out of RAM

5. Place results of processing in memory

PARTS OF CENTRAL PROCESSING UNIT (CPU)

1. Arithmetic and Logic Unit (ALU)

2. Memory Unit (MU)

3. Control Unit (CU)

MEMORY UNIT (MU)

The memory unit of CPU is the place where the computer program and data are stored

during processing. It is a random access storage device consisting of thousands upon

thousands of storage locations, each of which can be directly reached by the control unit.

Each storage location is distinguished by a unique number called its Address. During a

processing procedure, different data may be stored in any given storage location, but the

address of the storage location is fixed. For example: the memory unit is often compared to

a post office. At various times different letters are placed in a postal box, but the box

number is always the same.

Following are the basic functions performed by the memory unit:

1. Having all the data to be processed and the instructions required for processing

(received from input devices).

2. Having intermediate results of processing.

3. Having final results of processing before these results are released to an output device.

ARITHMETIC LOGIC UNIT (ALU)

The arithmetic logic unit (ALU) of a computer system is the place where the actual

execution of the instructions takes place during the processing operation. All calculations

are performed and all comparisons (decisions) are made in ALU. Data stored in primary

storage before processing, transferred as and when needed to ALU where processing take

place. After processing data transferred to primary storage, so data may move from primary

storage to ALU and back again to storage many times before processing is over. After the

completion of processing, the final results which are stored in the storage unit are released

to an output unit.

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Following are the basic functions performed by the arithmetic and logic unit:

1. It performs arithmetic processing like addition, subtraction, multiplication and division.

2. It performs logical processing like less than, greater than, equal to etc.

CONTROL UNIT (CU)

It is the control unit who tell the input unit that it is time for it to feed data into the memory

unit. It also handles ALU to tell what should be done with the data when it receives it.

Control unit is also responsible to send only the final results to output device not the

intermediate results. It is the responsibility of control unit to maintain order and direct 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. It manages and coordinates the entire computer system. It obtains instructions

from the program stored in main memory (RAM), translate the instructions, and issues

signals that cause other units of the system to execute them.

Following are the basic functions performed by the control unit:

1. It controls all the units or parts of computer system directly or indirectly.

2. Directly control to ALU and MU.

3. Indirectly control to input and output units.

2.2.1.3 OUTPUT UNIT

Output unit can be defined as:

“Unit which is used to get data from

the computer to user is called the output unit”

This unit supplies information and results of computation to the outside world. Thus it links

the computer with the external environment. As the results are in the binary form, so the

conversion of these binary codes to user understandable form is the responsibility of output

devices (i.e. monitor, printer etc.)

Following are the functions performed by the output unit:

1. It accepts the results produced by the computer which are in coded form and hence

cannot be easily understood by us.

2. It converts these coded results to human acceptable(readable) form,

3. It supplies the converted results to the outside world.

2.3 TYPES OF COMPUTER HARDWARE

As we already defined and briefly explained the hardware components of any computer

system, now here we will discuss in detail about different types of computer hardware as

shown in the following figure.

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Figure 2.5

“Basic Types of Computer Hardware”

2.3.1 MOTHERBOARD

Motherboard can be defines as:

“All the physical components of computer

reside on a circuit board called the motherboard (or mainboard)”

It is the primary circuit board within a personal computer. Components connect directly or

indirectly to the motherboard. Motherboards usually contain one or more CPUs, supporting

circuitry -- usually integrated circuits (ICs) providing the interface between the CPU memory

and input/output peripheral circuits, main memory, and facilities for initial setup of the

computer immediately after being powered on. A motherboard also contains one or more

peripheral buses and physical connectors for expansion purposes. Sometimes a secondary

daughter board is connected with the motherboard to provide further expandability or to

satisfy space constraints.

2.3.2 INPUT-OUTPUT DEVICES

The input-output devices provide the means of communication between the computer and

the outer world. They are also known as Peripheral Devices because they surround the PC.

Input devices are used to enter data into the primary storage and output devices accept

results from the primary storage to supply them to the users or to store them on a

secondary storage device for future processing. There are some devices which are used

for both the input and the output functions.

Computer System

Hardware

Input/Output

Devices

CPU

Memory

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Figure 2.6

“Types of Devices”

2.3.2.1 INPUT DEVICES

We will discuss about input devices, but first to know that what is input and what is device.

INPUT

The word “input” can be defined as:

“It is a process to enter something”

DEVICE

The word “devise” can be defined as:

“Device is purely based on electronics circuits”

INPUT DEVICE

Input devices can be defined as:

“A device which is used to accept data from the user, translate it

into computer understandable form and sends to internal parts

for further processing”

The input unit receives the input of data which is in need of processing. For this purpose

different input devices (i.e. keyboard, mouse etc) can be used. These devices are helpful to

make connection between the outer environment and the inner environment of the

computer. The data provided by the input devices to the computer is transformed into the

binary codes which are acceptable by the computer memory.

Computer System

Hardware Software

System

Application

Devices

CPU

Memory

Input

Devices

Output

Devices

Input-Output

Devices

Standard

Non-Standard

Standard

Non-Standard

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Figure 2.7

“Hierarchy For Input Devices”

FUNCTIONS PERFORMED BY AN INPUT DEVICE

Following are the functions performed by the input unit:

1. It accepts (or reads) the list of instructions and data from the outside world.

2. It converts these instructions and data in computer acceptable form.

3. It supplies the converted instructions and data to the computer system for further

processing.

TYPES OF INPUT DEVICES

Mainly we can divide the input devices into two categories:

1. Standard input devices

2. Nonstandard input devices

STANDARD INPUT DEVICES

Following two devices are considered as the standard input devices because these are the

most probably found input devices with most of the computers:

1. Keyboard

2. Mouse

NON-STANDARD INPUT DEVICES

Input devices other than “Standard Input devices” are considered as the non-standard input

devices. Following are the examples of some non-standard input devices:

1. Scanner

2. Joystick

3. Light Pen

4. Digitizing Tablet

5. Hand Tracker

6. Track Ball

Computer System

Hardware

Devices

Input Devices

Standard Non-Standard

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7. Track Points

8. Track Pads

9. Speech Recognition System i.e. Microphone

10.Vision Input System i.e. Digital Camera etc.

KEYBOARD

Keyboard can be defined as:

“A Keyboard is the standard data input and operator control

device for a computer”

Most computers would be useless without keyboard. Keyboard is a main device through

which computer receives users input. It is good for entering alpha numeric data. The

computer encodes the keyboard characters using the American Standard Code for

Information Interchange (ASCII). Each key has a unique 7-bit ASCII code associated with

it, with which we can communicate with the computer. The common arrangements of

alphanumeric keys on keyboard is called QWERTY layout (first six keys on the top row of

letters). Among IBM-compatible computers, the most common layout is the IBM Enhanced

Keyboard. It has 101 keys arranged in six groups.

TYPES OF KEYBOARD

There are two types of keyboards:

1. General Function Keyboard

2. Special Function Keyboards

GENERAL FUNCTION KEYBOARDS

These are traditional input device also known as “alphanumeric keyboards”.

SPECIAL FUNCTION KEYBOARDS

These are the keyboards designed to perform input of special type of data in a special way.

Sometimes these are designed for special persons.

IBM-COMPATIBLE KEYBOARD LAYOUT

Among IBM-compatible computers, the most common layout is the “IBM Enhanced

Keyboard". It has 101 keys arranged in following six groups:

1. Alphanumeric keys

2. Modifier keys

3. Numeric keypad

4. Function keys

5. Cursor-movement keys

6. Special-purpose keys

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Figure 2.8

“IBM-Compatible Keyboard Layout”

THE ALPHANUMERIC KEYS

Along with keys that produces letters (A to Z and a to z) and numbers (0 to 9), the

alphanumeric key group includes a few additional keys, with special functions. Following

are the names and details of these keys:

Tab:

1. It moves cursor to predefined tab stops in many application programs (such as in

word processors).

2. In dialog boxes, we can press Tab to move from one option or field to another.

Caps Lock:

1. It locks the alphabet keys to so they produce only capital letters. Caps Lock does not

affect the numeric keys or the keys that produce punctuation or special characters.

Backspace:

1. It enables us to erase characters we just typed or to erase a character present at the

left of cursor.

Spacebar:

1. it jumps for the space of single character.

Enter:

1. It is also known as Return Key. It lets us finalize data entry in many types of

application programs.

2. We can use it to choose a command or option in many programs.

THE MODIFIER KEYS

These keys are used to modify the input of other keys. We press another key while holding

down a modifier key. Following are the names and details of these keys:

Shift:

1. When we press a Shift key with the combination of any alphanumeric key, it forces

the computer to output a capital letter or symbol.

2. We can use it with Cursor-Movement Keys to select text for editing.

Ctrl:

It is an abbreviation of “Control”. Produces different results depending upon the program

used. For example:

1. In many Windows-based programs, Ctrl-key combination provides shortcuts for

menus commands i.e. Ctrl+S is for saving a file.

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Alt:

It is an abbreviation of “Alternative”. Operate like Ctrl-key, except that it produces a

different set of results. For example:

1. In many Windows-based programs, Alt-key combination enables us to navigate

menus and dialog boxes without using mouse.

THE NUMERIC KEYPAD

It usually located on the right side of the keyboard. Looks like an adding machine, with its

ten digits (0 to 9) and mathematical operators (+, -, * and /). The Numeric keypad also has

a Num Lock Key.

Num Lock:

1. When Num Lock is deactivated, the numeric keypad‟s keys perform cursor

movement control and other functions.

2. When Num Lock is activated, the numeric keypad‟s keys perform their functions of

using digits and mathematical operators.

THE FUNCTION KEYS

The keys are usually arranged in a row along the top of the keyboard, these are twelve in

number from F1 to F12. Each Function key‟s purpose depends on the program we are

using. For example, F1 is the help key.

THE CURSOR-MOVEMENT KEYS

These help the users to move around the screen by changing the position of cursor. Most

keyboards include the following standard cursor-movement keys:

Arrow Keys:

These are four in number and labeled by arrow pointing in a specific direction.

1. These keys move the cursor up or down a single line, or left or right one character

space.

2. Their behavior can be modified by using Shift and/or Crtl keys, depending on the

program we are using e.g. to move a greater distance or to select text for editing.

Home/End:

Depending on the program we are using:

1. We maybe able to press Home to move the cursor to the beginning of the line and

End to move the cursor at the end of the line.

2. Used with the combination of modifier keys, Home and End may move the cursor

greater distances.

Page Up/Page Down:

They let us “flip” through a document, screen by screen like turning the pages of a book.

1. Press Page Up to jump to the previous screen. Press Page Down to jump to the next

page.

2. Their function maybe affected by modifier keys, depending on the program we are

using.

SPECIAL-PURPOSE KEYS

In addition to the five groups of keys described, IBM-compatible keyboards features six

special-purpose keys, each of which performs a special function:

Insert:

1. It may be used to switch a program:

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a) From “insert Mode” i.e. where text is inserted into the document at the cursor.

b) To “Overtype Mode” i.e. where new text is typed over existing text.

2. The function insert maybe affected by modifier keys, or depending on the program

we are using.

Delete:

It is used to delete characters from document:

1. Used alone, Delete removes a single character at a time at the cursor„s location.

2. In combination with modifier keys and depending on the program we are using,

Delete may be able to remove multiple characters of text.

Note: The Delete and Backspace keys function is opposite ways. Delete erases

characters to the right of the cursor and Backspace erases characters to the left of the

cursor.

Insert and Delete keys are also known as Editing Keys.

Esc:

Its function depends on the program or operating environment.

1. Generally it is used to “back up” one level in a multilevel environment.

Print Screen:

This key allows the user to capture whatever is shown on the screen as an image. The

image can be printed, pasted into a document, or manipulated in various ways of the

software.

Scroll Lock:

Its function depends on the program or operating environment.

1. Usually this key controls the functions of the cursor-movement keys.

2. In some programs (e.g. in MS-Excel), it causes the cursor to remain stationary on

the screen, and the document‟s contents move around it. When it is turned off, the

cursor moves normally, (this does not function at all in some programs).

Pause:

In some programs, the Pause key can be used to stop a command in progress.

Start:

It is sometimes called “Windows logo key”, as it has the Windows logo on it.

1. It opens the Start menu in Windows 95, 98, 2000 and NT operating systems, which

is same as clicking over Start button on taskbar.

2. This key can be programmed to perform other tasks.

Shortcut:

It is sometimes called “Application key”, as it can be programmed to open a specific

application instantly.

1. It has the image of a menu.

2. It opens an on-screen shortcut menu in Windows-based application programs, which

is same as right-clicking within a Windows application window.

MOUSE

It is an input device used to control the position of the cursor and moves it around the

screen. It is a “point and draw” input device.

“A Mouse is a point and draw type of

standard input device that rolls

around on a flat surface and controls

the pointer”

Figure 2.9

“A Mouse”

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The mouse is mainly used in the GUI (graphical user interface) environments. Mouse has a

right and left buttons in common. Many recent mice have a scroll wheel as the middle

button. There are new mice that don't have a ball at all. They use a laser to sense the

motion of the mouse instead.

FUNCTIONS/OPERATIONS OF MOUSE

Following are the functions of a mouse:

1. Pointing

2. Clicking

3. Double-clicking

4. Dragging

5. Dragging and Dropping

6. Right-clicking

Pointing:

When we move the cursor of the mouse to an icon and leave it over there it is called

pointing.

Clicking:

While pointing to an icon if we press and release a button of the mouse there, it is called

clicking.

Double-clicking:

If we click and release quickly for two times this is called double-clicking.

Dragging:

If we point to a graphic icon, press button over there and hold it down and move our hands

across the screen, this function is called dragging.

Dragging and Dropping:

If we drag a graphical icon across the screen to our desired position and release the

pressed button over there then this function will be called to dragging and dropping.

Right-clicking:

If we point to a graphic icon, press right mouse button, a menu related to the properties of

that icon opens, this is called the right-clicking.

SCANNER

Scanners allow information such as a photo or text to be input into a computer i.e. it is used

to convert hardcopy into softcopy. Scanners are usually either A4 size (flatbed), as shown

below or hand-held to scan a much smaller area.

Scanner uses the LASER technology, and these are equipped with the Optical Character

Recognition (OCR) ability, which is the ability to read printed information into a computer

system.

KINDS OF SCANNER

Following is the list and then brief detail of each type of scanner:

1. Flat bed scanner

2. Hand held scanner

3. Sheet fed scanner

4. Slide scanner

5. Phot scanner

6. Drum scanner

7. Bar code scanner

8. Cross hair cursor machine

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9. Magnetic ink character reader (MICR)

10.Optical mark reader (OMR)

FLAT BED SCANNERS

They have a flat bed against which the printed information or graphics are placed, which is

then encoded and sent to the computer the information is displayed on the monitor.

Example: NADRA uses such type of scanners etc.

Figure 2.10

“Flatbed Scanners”

HAND HELD SCANNERS

These are moved in the document to be scanned and they encoded data into digitized

form. These can scan a book without breaking it.

Example: These are used to read data on price tags, shopping labels and inventory part

numbers etc.

SHEET FED SCANNERS

These scanners use motor driven rollers to pull the documents or data sheets to be

scanned through these devices.

SLIDE SCANNERS

These scanners use motor driven film holder that can pull a slide, film strip etc.

Example: These are mostly used in film industry etc.

PHOT SCANNERS

These are used to scan only the photos or film strips.

Example: These are mostly used in photo studios etc.

DRUM SCANNERS

In these scanners the media or data sheets to be scanned are attached to a rotating drum,

which rotates at speed of several thousands of rounds per minute.

BAR CODE SCANNERS

A bar code is a pattern printed in lines of differing

thickness. The system gives fast and error-free entry

of information into the computer.

Example: These are used to read data on price tags,

shipping labels and inventory part numbers etc.

CROSS HAIR CURSER MACHINE

This type of scanner is used to make cartoons, maps,

designs and photo like the image of Quaid-i-Azam on currency notes etc.

MAGNETIC INK CHARACTER RECOGNITION (MICR) SCANNER

Cheques and drafts in banks are written in special ink that had magnetic

elements included in it. These scanners are used in banks to recognize the amounts written

in such inks.

Examples: This method is used to run bank cash points or to provide quick identification of

people entering buildings.

Figure 2.12

“An Infra-red

Bar Code Reader”

Figure 2.11

“A Bar Code”

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Figure 2.18

“Hand Tracker”

OPTICAL MARK READER (OMR)

The Optical Mark Reader (OMR) can read information in the form of numbers or letters and

put it into the computer.

The marks have to be precisely located as in multiple choice test papers.

Example: Normally used in university to speedy checking of papers etc.

Figure 2.13 and 2.14

“Sample Multiple Choice Answer Papers”

JOYSTICK

The joystick is just like a lever. Similar to an aircraft's control stick, it

enables us to move within the screen's environment, and is widely

used in the computer games industry.

LIGHT PEN

A Light Pen is a pointing device shaped like a

pen and is connected to a Video Display Unit

(VDU). The tip of the light pen contains a light-sensitive element

which, when placed against the screen, detects the light from the

screen enabling the computer to identify the location of the pen on the

screen.

Light pens have the advantage of 'drawing' directly onto the screen, but this can become

uncomfortable, and they are not as accurate as Digitizing

tablets.

DIGITIZING TABLET

Consists of a pen and a pressure sensitive tablet. This enable

the user to perform pen based computing. Such as drawing and

entering handwritten data to the system.

A Digitising Tablet is a pointing device that facilitates the accurate

input of drawings and designs. A drawing can be placed

directly on the tablet, and the user traces outlines or inputs

coordinate positions with a hand-held stylus.

HAND TRACKER

A glove with sensors. While moving hand, sensor detects

the motion and gets the input from that motion. As a result

system gets input and respond accordingly.

Such hand tracker are used in video games and for training

purpose as well.

Figure 2.15

“A Joystick”

Figure 2.16

“A Light Pen”

Figure 2.17

“Digitizing Tablet”

Figure 2.19

“Track Ball”

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TRACK BALL

This is a ball inserted in an external box or fixed in the keyboard. The ball is rolled with the

fingers to move the graphic cursor.

TRACK POINTS

These work like a small joy stick and are operated with the

finger of the hand. Used in the video games or very commonly

used as a “remote control” of televisions, VCRs, security

systems etc.

TRACK PADS

Have no moving parts; simply we move finger about a touch

sensitive pad to move the graphic cursor. It is normally used in

laptops.

SPEECH RECOGNITION SYSTEM/ MICROPHONE (VOICE

DATA ENTRY)

This system accepts the spoken words as input data or

commands. Human speech is very complex, involving emphasis and facial expressions, so

complete voice recognition will not be developed for some time.

However, simple commands from one user can be

used to control machines.

In this way a paralyzed person can operate a

wheelchair or control heating and lighting. Sales

personnel in the field, surgeons in the operation

theatres and workers on airports etc. use such

devices. Microphone is a good example of such devices.

VISION INPUT SYSTEM

A computer does not see and interpret an image in the way as human

beings do. Digital Stills Cameras capture an image which is stored in

memory within the camera. When the memory is full it can be erased

and further images captured.

The digital images can then be transfer from the camera to a

computer where these can be displayed, manipulated or printed.

Web-cam is another example of vision input system used for

communication over the Internet.

2.3.2.2 OUTPUT DEVICES

We will discuss about input devices, but first to know that what is input and what is device.

OUTPUT

The word “output” can be defined as:

“It is a process to get something”

OUTPUT DEVICES

Figure 2.20 “A Track Point”

Figure 2.21

“A Touch/Track Pad”

Figure 2.22

“Microphone”

Figure 2.23

“Digital Cameras”

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Output devices can be defined as:

“A device which is used to get processed data called information,

translate it into user understandable form,

and gives output”

These are the devices which are purely used to get information from the computer or these

are the devices through which computer communicates with the outside world, the output

may be in the form of display (i.e. monitor), voice (i.e. speaker) or in written (i.e. printer).

Figure 2.24

“Hierarchy For Output Devices”

FUNCTIONS PERFORMED BY AN OUTPUT DEVICE

Following are the functions performed by the output unit:

1. It accepts the results produced by the computer which are in coded form and hence

cannot be easily understood by us.

2. It converts these coded results to human acceptable (readable) form,

3. It supplies the converted results to the outside world.

KINDS OF OUTPUT DEVICES

Output devices can be classified into two ways:

1. Standard and Nonstandard output devices

2. Softcopy and Hardcopy output devices

STANDARD OUTPUT DEVICES

Following two devices are considered as the standard output devices because these are

the most probably found output devices with most of the computers:

1. Monitor

2. Printer

NON-STANDARD OUTPUT DEVICES

Computer System

Hardware

Devices

Output

Devices

Hardcopy

Softcopy

NonStandard

Standard

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Output devices other than “Standard Output devices” are considered as the non-standard

output devices. Following are the examples of some non-standard output devices.

1. Plotter

2. Speaker

3. Computer Micro File (COM)

4. PC Projector or LCD Projection panels etc.

SOFTCOPY OUTPUT DEVICES

These are the devices, which are used to produce a softcopy of the output. Softcopy can

be seen or heard i.e. it is the copy of document inside the computer. When power is

switched off this copy is vanished, so a softcopy of a document is of temporary nature.

Following is the list and brief detail of softcopy output devices;

1. Monitor

2. Speaker

3. PC Projector etc

MONITOR

Monitors can be defined as:

“It is a softcopy, standard output device,

used to graphical type output”

It is widely in use and also known as Display Unit,

Screen, Display Screen, Video Display Terminal

(VDT), Video Display Unit (VDU), Screens,

Cathode Ray Tube (CRT), Liquid Crystal Display

(LCD) etc. There is a cathode ray tube installed in

monitors. Monitors vary in their quality of output

called Resolution. The larger the number of pixels

the finer is the resolution. The high resolution

monitors give extremely clear images that look almost like a photograph. Their sizes vary

from 3 inches to 30 inches but 14”, 15”, 17”, and 21” are the standard sizes.

KINDS OF MONITORS

Monitors can be classified according to:

1. Display

2. Resolution

3. Screen size

4. Volume

KINDS OF MONITORS - ACCORDING TO DISPLAY

There are three kinds of monitors according to their display:

1. Monochrome

2. Grayscale

3. Color

MONOCHROME MONITOR

These monitors display images in a single color, usually white, green, blue, red or amber

(yellowish brown color). These monitors are becoming outdated.

GRAYSCALE MONITORS

Figure 2.25

“CRT Structure”

21

These monitors displays us the shades of gray on a white or off-white background. These

monitors are also becoming outdated.

COLOR MONITORS

Color monitor mix red, green and blue (RGB) to achieve a spectrum of colors. Four most

popular monitors are:

1. CGA or Color Graphic Adopter, which offer four colors.

2. EGA or Enhanced Graphic Adopter, which offers 16 colors.

3. VGA or Video Graphic Array, which offers 256 colors.

4. SVGA or Super Video Graphic Array, which offers up to 16 million colors.

5. XVGA or Extended Video Graphic Array, which offers up to 16.7 million colors.

KINDS OF MONITORS - ACCORDING TO RESOLUTION

There are two kinds of monitors according to their resolution:

1. High resolution

2. Low resolution

HIGH RESOLUTION

Good quality of text and graphics on the screen.

LOW RESOLUTION

Low quality of text and graphics on the screen.

KINDS OF MONITORS - ACCORDING TO SCREEN SIZE

A monitor is available in different screen sizes:

3 to 30 inch screens are available in the market. 15 and 17 inch screens are common now

a day.

KINDS OF MONITORS - ACCORDING TO VOLUME

There are two kinds of monitors according to their volume:

1. CRT (Cathode Ray Tube)

2. Flat – Panel Tube

CRT (CATHODE RAY TUBE)

Monitor of this type screen are used commonly in homes, colleges

and offices. These monitors are big and required big area to place,

power and have weight more than 10 pounds like TV. We can not

move these monitors easily.

FLAT – PANEL TUBE

These monitors are also available nowadays in market. These

monitors are normally used in Laptop computers and we can also

use these monitors in desktop computers, there are several types

of flat-panel monitors, but the most common is Liquid Crystal

Display (LCD).

All of these monitors are widely used today. VGA and SVGA, with

high resolution, with CRT and with 15” and 17” of screen size of

monitors are fine for most business and home

applications. Figure 2.27

Crystal Display (LCD)

Figure 2.26

“CRT Monitor”

22

SPEAKER

Speaker can be defined as:

“It is a softcopy, standard output device,

which is used to give the output of sound type of data”

Speakers are known as the Voice Output Devices or Voice

Response System. Like monitors, voice response systems

provide a temporary, soft copy output.

Example:

Educational applications include "Speak & Spell" trainers.

PC PROJECTOR

Portable computers are rapidly replacing old fashioned slide projectors and overhead

projectors. A PC projector plugs into computer‟s video output port and projects the video

output onto an external surface. These small devices typically weight less that 3kg and can

display over 16 million colors at resolution upto 1024 x 1024 dpi (dots per inch). Some PC

projectors can be converted from still-video (slides) mode to full-motion video mode, to

display output from a VCR or DVD player.

Figure 2.29

“PC Projector and its usage”

HARDCOPY OUTPUT DEVICES

Following is the list and brief detail of hard copy (permanent) output devices:

1. Printer

2. Plotter

3. Computer Micro File (COM) etc.

PRINTER

Printers can be defined as:

“It is a hardcopy, standard output device,

which is used to give the color or back and white

printing of any type of data”

It is also known as primary/standard output device. The output we get from printer is a hard

copy output i.e. these are used to get output over a paper. We can make black and white

and colored copies with the help of printers. The quality and price of any printer depends

upon two factors:

1. Dots per inch

2. Number of characters/words per minute

TYPES OF PRINTERS

There are many types of printers but according to working there are two types of printers:

Figure 2.28

“A Speaker”

23

1. Impact Printers

2. Non-impact Printers

IMPACT PRINTERS

When these printers work their keys strike on ribbon against the paper and leave the

impact of keys on the paper to produce the print, like typewriter. Creates an image by

using pins or hammers to press an inked ribbon against the paper

These can make carbon copies of the print also while printing.

CHARACTERISTICS OF IMPACT PRINTERS

These printers are:

1. Based on older technology

2. Give effect on paper

3. Cheaper

4. Much noisy

5. Performance is not good

6. Slow in speed

7. Do not have advanced features of printing

8. Can not print multiple pages

9. Can not print on transparencies

10.Can not support for multiple carbon copies

11. Performance is measures in terms of Characters Per Second (cps) or