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
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