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Published by abhishek54yt, 2021-10-27 05:25:26



Fundamental Knowledge of Computer System


A computer is a programmable device that accepts, processes and
stores the data. A computer is an electronic machine used to perform the various
mathematical and logical calculations based on the instructions provided by the
user. It takes the data and instructions as input, processes them, produces the
output and stores the results.

The word computer is derived from the Greek word ‘computare’, which
means calculate. Actually, a computer is a collection of hardware and
software components that help us to complete many different tasks at
enormous speed.
Advantages of computer:
v Computer is fast and accurate machine.
v Computer is a versatile machine.
v It can feature high storage capacity.
v It is a diligent and reliable machine.

Disadvantages of computer:
v It is expensive system.
v It requires electricity to operate.
v Its extensive use is creating unemployment problem.
v It enables people to commit crime virtually.

v It is non-intelligent device.

Working Principle of the Computer system:

A computer system is the combination of different hardware and software
components that basically solves the problem of the user which works on the
principle input-process-output.

fig:- IPO cycle

Inputs are the data and instructions entered to the computer using
different input devices like keyboard, microphone, mouse, scanner etc. Input cycle
involves data capturing, data collection and data checking and converting it into
machine readable form.

After the input is given to the computer, its starts to process the data

to derive output which will be displayed by the various output devices in the
human understandable manner. The Central Processing Unit (CPU) is
responsible for doing the job of data processing.

After the data processing, the meaningful output is delivered to the

computer user via different output units like monitor, speaker, printer etc.

Characteristics of computer

1. Speed:

The time taken by the computer to execute instructions given and to

perform any operation is called the processing speed. Computer works at an
amazing speed taking just few seconds to execute billions of instructions. The
computer’s speed to perform a single task assigned can be measured in terms of
millisecond, microsecond, nanosecond, picosecond and femtosecond.

Data processing speed is one of the factor that makes computer a
powerful machine.

Computer needs just fraction of second to perform simple to complex calculations.
The fraction of second are given below:

Unit of time Part of second
Millisecond (Ms) 1 / 1000 of a second
Microsecond (µs) 1 / 1 million of a second
Nanosecond (Ns)
Picosecond (Ps) 1 / 1 billion of a second
Femtosecond (Fs) 1 / 1 trillion of a second
Altosecond (As) 1 / 1 zillion of a second
1 / 1018 of a second

2. Electronic:

A computer is an electronic device which can perform calculations
and control operations. Most of the computer parts are electronic devices which

are made of semiconductor chips.

3. Storage

A computer features the storage capacity according to the
requirement of the user. It can store a large volume of data permanently. User

can store any kind of data like audio, video, pictures, textual files and
documents easily. You can quickly and efficiently organize the information
which can be easily and instantly retrieved when needed.

Computer memory is measured in terms of bytes, KB, MB, GB, TB

Following chart defines each terms. 1 Bit
0 or 1
1 Nibble
4 Bits 1 Byte
8 Bits or 2 Nibble 1 Kilo Byte (KB)
1024 Bytes 1 Mega Byte (MB)
1024 KB
1 Giga Byte (GB)
1024 MB 1 Tera Byte (TB)
1024 GB 1 Peta Byte (PB)
1024 TB 1 Exa Byte (EB)
1024 PB

4. Accuracy

Accuracy means to provide results without any error or mistakes.
Computers can process large amount of data and generate almost 100% error free

But sometimes we get the false result due to faults in the data,
instructions or program which is known as Garbage in Garbage out(GIGO).

5. Versatility
A computer is a versatile machine as it can perform various tasks with

the same ease and efficiency and also at the same time. It can be used for various
purposes such as accounting, generating pay slip, playing games, listening music,
watching movies, typing and printing the documents, sending email etc.

6. Diligence
Unlike humans, a computer never feels tired and bored and to do a

task repeatedly for a long time. It can perform same task with the same speed
and accuracy even for hours and days if it is provided with the suitable
environment and correct program.

7. Non-intelligent
Although the computers are faster, accurate and powerful than the

humans, it does not have common sense and can’t think and decide itself to do
any task.

8. Automation
Computers can be programmed to perform a series of complex tasks

9. Word Length
The power of the computer depends upon the word length. It refers to

the number of bits that the CPU can process in parallel at a time. Usually
computers have 8,16, 32 or 64 bit word length.

Basic computer terminologies:


Data are collection of raw facts and figures which doesnot bear any specific
meaning. Data are unprocessed pieces of information.


Information are the sequence of data and instructions presented in a systematic
way. It can be understood as meaningful result.


Commands are the instructions or order given to the computer to perform any
specific task.


It is the huge collection of instructions arranged together in a specific order to
solve the problems and make computer functional.


A software is a set of programs and all the necessary files and documentation that
tells the computer what to do and how to do. Software are the abstract part of the
computer system that utilizes the hardware parts.
Eg :-Windows, VLC media player, MS-word etc.


The physical parts of the computer system which performs various actions as
instructed by the software are known as computer hardware. Eg :- monitor,
microprocessor, speaker, keyboard, joystick etc.


Computer memory are the hardware parts which stores the data, information,
programs and software temporarily or permanently.
Eg:- RAM, ROM, Hard disk, pen-drive ,SSD etc.

Societal Impacts of Computers

Computer system has become the integral part of our day to day life.
Computer have made such an immense impact on our society. It has shaped the
way of living, thinking and working. Computers can be used in almost all the
sectors of society to enhance the existing process.

Computers can be used in the various fields like in banks, medicine,
education, ticketing, defense, multimedia, desktop publishing, communication,
data processing, weather forecasting etc.
A broad classification of how it can be used in various fields are explained below:

• Computers in Education

Computers and information technology has literally changed the
teaching and learning process. It has made the learning process effective and
interesting. A student can use ICT tools to do research, make presentation,
prepare and submit assignments, consult with teachers and discuss with friends
on any topic. They can take online classes, search course learning materials, fill
up form online etc. using internet. Use of computers in the classroom will explore
the creativity and imaginations in students’ mind. Drawing tools, spreadsheets,
audio-video lectures, PowerPoint presentations etc. are very beneficial for
students to learn more deeply and accurately. Internet has become the huge
source of knowledge for everybody.

• Computers at Home

The use of computers at home depends on the user. Some people use
computer for the entertainment purposes like watching movies, listening to
music, connect with friends and family. Some are using it to learn new skills and
hobbies. We can use computers to calculate the monthly expenses using MS-excel.
We can document our daily interesting events with MS-word. We can edit, restore
and manipulate our family photographs. We can do online business, take online
classes and online shopping. Its’ uses and possibilities at home are endless.

• Computers at Banks

The use of computers in banking sector is saving the productive time
of the customers and providing them the better service. Banks are using
computers software to record all the financial transactions. Banks use computers
to provide the services like online banking, ATM cards, electronic payments,
mobile banking, etc. which allows them to provide 24 hrs service with less effort.
Also whenever we deposit or transfer fund we get the notification messages. We
can see and print our statements without visiting banks. We can also gather the
knowledge about various banking schemes related to loan, interest rates, fixed
deposit, investments etc. just sitting at home. More over use of computers in
banks has changed the way we use and manage our funds.

• Computers in Business and Industry

Computers in business are used to store information, generate plans,
scheduling appointment and deadlines etc. In the past few years, computer has
been the primary tool to run a successful business. It can be used for
manufacturing products, advertisements, recording sales and supply, be in touch
with customers, provide pre & post sales service etc. Companies can conduct staff
training, run virtual meeting and share important information and reports using
computers and internet. In short computer can help business industry a lot
increase the productivity & profit and limit the operational cost. E-commerce does
exist just because of computers.

In industries, computers are used to control and automate huge
number of machines to create, assemble and test their products. Many industries
use Computer Aided Design (CAD) to design products and Computer Aided
Manufacturing (CAM) to produce them.

• Computers in Medicine

The use of computers in medicine fields can play very important role
in improving the health care for individuals and communities. It also provides the
capacity to prevent medical errors. It provides benefits for both doctors and
patients. Hospitals can use computer to create the database of the patient with
their treatment records and medical history. Computerized systems in hospitals
helps to do the research on disease, blood test, urine test, brain testing and body
scanning etc. They are also used to monitor vital data during surgery in operation

• Computers in Law and Order

Computers plays serious and vital role in managing the peace in our
society. Law enforcement agencies like police department uses computer to keep
and search the information about criminals and suspects. Use of CCTV camera,
dash cam and body cam helps to capture the crime scene which can be used to
extract the evidence and trace the culprits. Fingerprint and facial recognition
software helps the police department to detect and investigate the criminals.

Lawyers also use computer to prepare case files, do research and
present the evidences in the court.

• Computers in Government

Government works and official works used to be very time consuming
in the past. Use of computers in governmental bodies has now made the process
hassle free. Now citizens are given better service with the concept of e-governance.
Number of unnecessary staff members are also cut with use of computer in
government offices which is cutting the extra expenses.

• Computers in Entertainment

Entertainment industry heavily relies on the computer and its
products. Computers are used in the movie industry create special effects in the
audio and video as well as edit it. They are used in composing, reproducing and
recording music. Computer also allows user to play video games which are quite
interesting and entertain the user to the fullest.

Multimedia components of computer enhances the experience of
movies, pictures and games.

Positive Impacts of Computer

v It facilitates business process making it simple and less time consuming.
v It provides greater access to information.
v It can be used for communication system.
v It can be used in education, banking, defense and various other fields.
v We can prepare and store documents in computer securely.
v It gives error free result.
v It helps to share ideas, opinions, news and views in faster and reliable way.
v It offers significant potential in improving personal skills.

Negative Impacts of Computer

v It gives rises to the security concerns.
v It can be used to commit cyber-crimes.
v It may not be accessible in the remote areas.
v It helps spread false and fake news sometimes.
v Social disconnect.
v Decreases productivity.

A Look Inside the Computer

A computer system is a combination of inter-related and
interdependent components that interact regularly to perform a task. It uses
various units for accepting the input, processing it, displaying the results and
storing them as required. A computer system functions effectively when all these
components perform their assigned job. The failure of any one component of the
system leads to the failure of the whole system. Information is communicated
between these separate units by the system bus. The system bus connects the
CPU to the other components that reside on the motherboard.

Major parts of a computer system:

• Hardware: Hardware are the tangible parts of the computer

system which can be physically handled. For computers, hardware

means the Central Processing Units (CPU) and all the peripherals.

• Software: A software is the set of instructions which tells the

computer what to do, how to do and when to do it. These are the logical

components which that make physical components work.

• Data and Information: Data are the unorganized and

unprocessed facts. Information are the meaningful result derived from

the data processing.

Data Information
v Data are unprocessed facts.
v Data are used as the input. v Information is processed data.

v Data do not hold specific v Information is the output of
meaning. data.

v Data are raw material. v Information carry a logical

v Information is the product.

• Humanware: The computer users are the humanwares. A computer
system holds no purpose and meaning if there are no users to instruct

it and make it functional.

Block diagram of Computer System

Data Flow
Control Flow

The Processor
Control Unit

Issues commands to all elements of
It makes a sequence of control flow
and data flow

INPUT Arithmetic & Logic Unit OUTPUT

Data and It performs mathematical and Information
Instructions logical calculations.
(Audible & Visible)
Main Memory

Holds data, instructions and
results of processing

Auxiliary / Storage Memory

To supplement the
main storage

Computer Hardware

Computer hardware are the physical parts which makes the entire
computer system. Hardware equipment can be magnetic, electronic, mechanical
and electrical devices. These hardware parts work together with the software and
programs to read the raw data, manipulate it, store and finally display the output.
The different hardware units are:

a. Input Devices
b. Central Processing Unit
c. Output Devices
d. Storage Devices

v Input Units: Input means to feed or put data into the computer system.
Inputs can be any data, program, commands or user responses. Input
devices are used to collect or capture data, check data and convert it into
binary form which can be understood by the CPU. Some common input
devices are keyboard, mouse, scanner, magnetic disk reader, joystick,
touchpad etc.

There are three types of keyboard as:

i. Standard Keyboard (84 keys)
ii. Extra Technology Keyboard (101 keys)
iii. Advanced Technology Keyboard (103 Keys)

There are three types of keyboard as:

i. Mechanical Mouse
ii. Opto-mechanical Mouse
iii. Optical Mouse

v Central Processing Unit: Processing hardware CPU is responsible to
process all the activities from data entry stage to output stage. It handles
all the actions of the computer system and makes the computer functional
that is why a CPU is known as the brain of the computer. Nowadays, the
CPU is built on a single chip is called microprocessor. It is usually mounted
on the motherboard and connected to various peripheral devices using bus
(Printer Wires).
The processing capability of CPU is measured in terms of MHz
or GHz. Clock speed determines how many instructions per second the
processor can execute.
For example: 3.2 GHz means the CPU can execute 3.2 billion cycles per
Bandwidth of CPU means number of bits processed in single instruction.

Pic : Motherboard

Major components of CPU

i. Control Unit
ii. Arithmetic and Logic Unit
iii. Primary Memory

i. Control Unit: The CPU is called the brain of the computer system. In fact,
control unit is the brain inside the brain. It controls the overall operations
such as I/O operations, processing operations and memory managements. It
directs the movement of data flow and control flow in computer system.

Functions of Control Unit
a. It gives command to transfer data from input devices to memory
units to ALU.
b. It also transfers results from ALU to memory and then to output
c. It stores program in the memory.
d. It analyzes each instructions and decodes what operation is to be
e. It manages the control flow and data flow.

ii. Arithmetic and Logic Unit: It is the main processing unit within the

microprocessor that’s why it is known as the fundamental building block of

CPU. It performs the mathematical and logical operations using the data

and instructions. It contains registers, capacitors and accumulators.

Fig: The Fetch-Execute cycle

iii. Primary memory: The only memory unit that has direct connection with
the computer’s processor.

Computer Memory

Registers Cache RAM ROM Magnetic Magnetic Optical Flash
Memory Tape Disk Disk Memory
L1 DRAM EPROM Floppy CD Pen drive
Blue Ray
Disk Disk

The computer memory is a data storing device. It enables a computer
system to store the data and programs either temporarily or permanently. A
memory system can be logically divided into two categories as:

i. Primary memory
ii. Secondary memory

i. Primary memory: Primary memory is the fast and less capacity memory

of the computer system. They are mainly used to store the data during the
time of processing. It holds the data and instructions which can be accessed
by the microprocessor quickly.

RAM, ROM, Cache memory and Registers are the examples of primary

v RAM: Random Access Memory is a form of computer data storage

which stores data and allows the processor to access it in any order (random)

required. RAM is called volatile memory because its contents are lost as soon

as the computer is turned off.

Actually RAM are also built on a semi-conductor chip using
transistors and capacitors.

Types of RAM are: SRAM & DRAM

Static Random Access Memory Dynamic Random Access Memory
• It does not need periodic • It needs periodic refreshing.

refreshing. • It consumes high electrical
• It consumes less electrical power. power.

• It is faster than DRAM. • It is slower than SRAM.
• It is expensive. • It is cheaper than SRAM.
• Mostly it is formed using • Mostly it is formed using

transistors. capacitors.

v ROM: Read Only Memory is a class of memory device which is non-
volatile in nature as data stored in ROM are retained even after the power
is cut off. Data stored in ROM cannot be modified, or can be modified slowly
or with difficulty, so it is mainly used to distribute firmware.

Types of ROM are:

Ø PROM (Programmable Read Only Memory)
Ø EPROM (Erasable Programmable Read Only Memory)
Ø EEPROM (Electronically Erasable Programmable Read Only



Random Access Memory Read Only Memory

• Its contents will be erased when • Its contents won’t be erased when
power is off. (volatile) power is off. (non-volatile)

• It has higher storage space than • It has less memory space than

• It is faster than ROM. • It is slower than RAM.

• It is cheaper. • It is expensive.

• Types: SRAM & DRAM • Types: PROM, EPROM &

v Cache Memory: It is an extremely fast memory built into a computer’s

CPU or located next to it on a separate chip. The CPU uses cache memory

to store instructions that are repeatedly required to run a program which

results in performance improvements.

ii. Secondary Memory: Auxiliary memory devices are the slower and

cheaper memory units which provides the permanent data storage facilities.
CPU does not access its contents directly. The content in it must be loaded
into the RAM and to processor for processing. Some examples of secondary
memory devices are hard drives, CDs, DVDs, pen drive etc.


Primary Memory Secondary Memory
• It is not directly connected to the
• It is directly connected to the
processor. processor.
• It is less expensive than primary
• It is expensive than secondary
memory. memory.
• It is optical or magnetic memory.
• It is semi-conductor memory. • It is slower.

• It is faster than secondary • It has high storage capacity.

• It has low storage capacity.

Output Units

Output device is any peripheral device that receives and displays the
result obtained from the primary memory. Output can be any audible or visible
data and information. The output produced by the monitor and speaker are
softcopy output whereas the output printed on a paper is known as hardcopy
Functions of output units:

a. It accepts the results produced by computer in binary coded form.
b. It converts the results from machine code to human

understandable form.

Some examples: Monitor, Printer, Plotter, Speaker etc.


It is a collection of computer programs, procedures and documentation
that performs different task on a computer system. Software is defined as
instructions and associated data, stored in electronic format, that directs a
computer to accomplish a task.

Software is the means which, by which, computer systems speak with
computer users. It gives soul to the computer system.

Computer software can be classified into two types as:

1. System Software
2. Application Software

Programs Software
• It is the set of instructions to
• It is collection of instructions,
perform specific job. program and data that can
perform multiple tasks.
• It is component of software.
• It is a logical unit which drives
• It defines process in the the computer system.
• It defines both process and data.
• Eg: a program to calculate SI,
area of circle etc. • Eg: MS Word, Adobe Photosoph

Random Access memory
Read Only Memory

Types of Computer

Computers are classified on the basis of their working principle, size, brand and

On the basis of On the basis of
size brand

•Super •IBM Computers
•Mainframe •IBM Compatible
•Mini •Apple Macintosh


On the basis of On the basis of
function model

•Analog •XT (Extra Technology)
•Digital •AT (Advnaced " )
•Hybrid •PS/2

1st 2nd 3rd 4th 5th
Time Period Generation Generation Generation Generation Generation
Technology 1940-1956 1956-1963 1964-1971
1971-Till date Present and
Vacuum tubes Transistors IC beyond

Microprocessor AI , Bio-chips

Speed Milliseconds Microsecond Nanosecond Picosecond Femtosecond

Storage Magnetic Magnetic Magnetic disk Magnetic disk Same
tapes / drums tapes / disks & optical disk
I/O devices Keyboards & Keboards & Advance
Punched cards Punched cards Monitors Monitors Peripherals
Size, Cost, Power High Very Low Very Low
consumption, Very high High
Heat Natural
Programming MLL ALL & HLL HLL(3GL) HLL(4GL) language
language IBM 700, IBM 1401, ICL Robotics
Examples: ENIAC etc. 2950/10 etc. CDC 7600, IBM PC, Apple
IBM 370 series etc.


1. On the Basis of Working Principle

• Analog Computer:

The computer which is based on the continuous data is known as
Analog computer. Analog computer can only measure the physical or
natural quantities such as water flow, pressure, speed, current and
voltage etc. These computers are specific purpose computers specially
used in the field of physics and engineering. The accuracy of this
computer is very poor. It features no or less storage capacity. These
computers are cheaper in cost compared to digital computers. The
continuous signals passed to the computer is in the form of wave or
curve lines. Some examples of analog devices are: speedometer,
thermometer etc.

• Digital Computer:

Digital computer stores the data in terms of binary digits and proceeds
in discrete steps from one state to the next. It works with digits 0 and
1 to represent numerals, letters or other symbols. Digital computer
process information based on the presence and absence of electrical
charge. This computer works with discrete data. Digital computer is
used for general purpose. The accuracy of the digital computer is very
high. This computer features high storage capacity and are expensive
than the analog computers. Examples: IBM PC, IBM compatibles,
Apple Macintosh etc.

• Hybrid Computer:

The computers which have the capabilities of both digital and analog
computers are called hybrid computers. It can process both analog and
digital signals. It has the measuring feature of analog computers and
counting feature of digital computer. It accepts a continuously varying
input and which then are converted into a set of discrete values for
digital processing.
Examples: ECG machines, Devices used in the petrol pump etc.

Features of hybrid computer are
v It is very reliable and provides accurate results.
v These computers are very fast.
v It is mainly used in the robotics.
v These are special purpose computers.

2. On the Basis of Size

• Super Computers:

Super computers are the fastest digital computers which has the
immense processing power, huge storage capacity and very fast
input/output capability. It contains thousands of individual processors
which function simultaneously and variety of other technological
tricks to offer tremendous calculating power. It offers 128 bits
addressing capability.

Super computers are very expensive and are employed for
specialized applications. These computers are used by large
organizations for research and exploration purpose.
Examples: CRAY-XMP, CRAY-1, PARAM, Roger CRAY(1976) etc.

Uses of super computers

Space Exploration, Earthquake Studies, Weather Forecasting,
Nuclear Weapon testing etc.

Super computer

• Mainframe Computers:

Mainframe computers are giant computers after super computers
which can process millions of instructions per second and are capable
of accessing and manipulating billions of data. These computers are
used by large scale organizations for bulk data processing, commercial
data processing such as bank transaction processing. It is a general
purpose computer which can be used by thousands of users at once. It
offers 64 bits addressing capability

The main difference between super computer and mainframe
computer is that a super computer puts all its powers to execute a few
programs to get result as fast as possible whereas mainframe uses its
power to execute many programs concurrently.
Examples: CDC 6600, IBM 7090, IBM 1401, ICL 2950/10 etc.

• Mini Computers:

These are the midsized computers that are somewhere between
mainframe and micro-computers. It is a medium scale computer built to
perform complex computations. These computers are used by small business
organizations which are smaller, less expensive and less powerful than
super and mainframe computers. It is a general purpose computer with
multi-processing system that can support 4 to 200 users simultaneously.

Use: University, Scientific Research, Industries etc.
Eg: VAX-8800, MV-1500, PDP-8, HP 3000 etc.

• Micro Computers:

According to size, they are the smallest computers. It is a small digital
computer whose CPU consists of microprocessor, a single semi-
conductor integrated circuit chip. The desktop, laptop, mobile phones,
iPad etc. are the example of microcomputers.
Use: Entertainment, College and school, Business etc.
Eg: MITS Altair 8800, IMSAI 8080 etc.

3. On the Basis of Brand

• IBM Computers:

These are the computers manufactured by the IBM company which
was established by Herman Hollerith in 1923 AD. It is the largest
manufacturing company in the world which produces the most reliable,
durable and fast computers. All the parts in it are developed by IBM on its
own. Generally, they are expensive than other computers. IBM company is
leading company to manufacture super, mainframe and personal computer.

• IBM Compatible Computers:

The word compatible means ‘able to co-exist and work successfully’. So
in IBM compatible, the components are manufactured by different
companies and finally they are assembled to make a computer system. They
are cheaper than IBM computers.

• Apple / Macintosh:

Apple is the first trillion-dollar company which manufactures very
smart, durable, reliable and user-friendly computing machines. Its internal
architecture is totally different than IBM PC. The software used in Apple
computers can’t be used in IBM PC or vice-versa. Eg: iPhone, iPad, MacBook

4. On the Basis of Model

• XT (Extra Technology)
These are the old technology computers that uses character user

interface software. They don’t have high speed processor and enough storage
capacity. It can’t do complex calculations and large data processing.

• AT (Advanced Technology)
These are the modern day computers which uses both CUI and GUI

based software. Their I/O devices are interactive and faster. It features high
speed processor and larger storage capacity.

• PS/2 (Personal System): These are AT computers like laptop, mobile phones,
tabs etc.

Computer Hardware

Computer system is the integration of hardware and software units.
Hardware parts function in accordance to the set of instructions called program
and software. All hardware parts are controlled by the program loaded into the
computer system.

Hardware components of the computer system are the physical parts
of the computer system that are tangible such as keyboard, mouse, scanner,
microprocessor, joystick, printer, camera, memory units etc.

The functions of hardware is to accept raw data as input, manipulate
or process the data to derive valuable information, store the data and information
and finally display the required information as output.
Types of hardware:

1. Input Hardware
2. Processing Hardware
3. Output Hardware
4. Storage Hardware

1. Input Hardware

It accepts the data and instructions given by the user and converts the data
captured from man readable form to machine readable code. Input is any form of
information computer collects from the outside world.
Some of the input devices are as follows:

v Keyboard : The keyboard is the data entry platform of computer. It is

the primary input device to for entering the text and characters and also to
control the operation of the computer. Modern keyboard connects to with the
computer’s CPU by cable or by infrared transmitter. When a key on the
keyboard is pressed, a numeric code is sent to the keyboard driver software
and to the computer’s operating system software. The driver translates the
code into specialized command that CPU and application program

A keyboard contains different types of keys with various symbols such
as alphanumeric keys, navigation keys, functional keys and separate
numeric keys. All the keys in the keyboard are like switches connected to a
small keyboard microprocessor. When the user presses a key, it causes a
change in the amount of current flowing through the circuit associated
specifically with that key. The keyboard microprocessor detects this change
in current flow and determine when a key has been pressed and when it is
being released. Then the keyboard microprocessor sends the signals to the
operating system.

Types of keyboard are :

i. XT (Extended Technology Keyboard) : 85 Keys
ii. AT (Advanced Technology keyboard) : 101 Keys
iii. ET (Enhanced Technology Keyboard) : 103 or more keys

Pointing Devices

Pointing device is an input device used to move the mouse pointer and feed
instructions to the computers system. It is used to select items on a display screen,
to choose the options given and to draw images as desired by the users.
Some of the pointing devices are as follows:

v Mouse : A mouse is the point and click device which is used to input

instruction signals to the computer system by moving around and selecting

items in a graphical user interface. Generally, the mouse has two buttons

and a wheel with specific functions. The left one is used to select objects and

text. The right one is used to access menus. The wheel is used with specific

programs for scrolling upward and downward.

The cursor in the screen indicates where your control is
currently and it moves in the direction of the mouse’s movement.

Types of mouse :

i. Mechanical Mouse
ii. Opto-Mechanical Mouse
iii. Optical Mouse

v Trackball : A trackball is a stationary pointing device that contains a

movable ball rotated with finger or palm. It is the alternative to the mouse.

It also has one more buttons to initiate other actions. The major advantage
of track ball against mouse is that it takes little desktop surface and we don’t
have to move the whole unit, only the ball nestled on the cradle(base) will

v Joystick : It is the most popular input device for playing computer

games and Computer Aided Designing(CAD) & Computer Aided

Manufacturing(CAM). It is also used as flight control tool in cockpit of

aircrafts, cranes, trucks, surveillance cctv system etc.

It contains a vertical stick/stem placed on a rectangular

base. The stick has a spherical ball at its lower end as well as its upper end.
The lower ball moves in a socket. The joystick can be moved omni-
directionally. The movements are sensed by the potentiometer.

v Touchpad : Touchpad is a stationary pointing device that uses pressure

sensors to track the position of a device on its surface. The movement of
finger across a small touch surface is translated into pointer movement on

the computer screen. The touch sensitive surface may be only 1.5 or 2 inches
square. One drawback of touchpad is that it must be kept clean and static
free. Dust and oils from user’s finger may reduce the sensitivity and thus

v Digitizer : A digitizer is an input device used for tracing or copy a

drawing or photograph. It is also known as graphics tablet which enables a

user to hand-draw images, animations and graphics with a pen like stylus,

similar to the way a person draws images with a pencil and paper. It is

mostly used by the designers, architects and engineers.

v Touch Screen : Touch screen is a computer display screen sensitive

to human touch, allowing a user to interact with computer and navigate it

by touching pictures, program icons or words on the screen. It is suitable for

accessing information with minimum effort. This advanced technology is

applied in all sorts of smart computing devices these days. The same screen

which displays the output also takes the input in this technology. When the

screen is touched, computer sense where you have pressed and accordingly

it generates the input signals triggering various actions.

v Light Pen : A light pen is an special input device used to point to

displayed objects and highlight it and to draw images/text on the CRT
monitor screen with greater positional accuracy than touchscreen. It
consists of a photocell and an optical system placed in a small tube. When
the tip of the pen is moved over the monitor screen and the pen button is

pressed, its photocell (light sensor) detects the screen location and sends the
corresponding signal to the CPU. It can sense the sudden change in the
brightness of a point on the screen and accurately note the X, Y position of
the pen reach while scanning.

Optical Devices

Optical devices use light as source of input for detecting and recognizing different
objects such as characters and images. The examples of optical devices include
scanner, Optical Character Reader (OCR), Optical Mark Reader (OMR), Magnetic
Ink Character Recognition (MICR) etc.

v Optical Character Reader : OCR is an input device used to

recognize pattern in the image scanned to read the numeric and alphabetic

symbols. By using the reflection of light it scans the text character by

character and analyses it by matching the pattern of the scanned character

against stored information and then generates the corresponding ASCII

code of that character and writes it onto the memory as data. It is widely

used in image scanners to digitize the image and documents.

v Optical Mark Reader : OMR is an input device used to detect the

presence of intended marked responses. It is used to scan the forms to read

the answer sheet of multiple choice questions, survey form, voting

application etc. In this technology, the paper forms are placed under the

light source, and the resultant reflection of light in the other side of paper is

analyzed as a mark always registers significantly less light than other area

in the paper. The presence of dark ink is transformed into the electric

signals which are transmitted to the computer.

v Scanner : Image scanner is a light sensing device that translates

images and other printed / hand written information into the digital form so

they can be stored and manipulated by the computer. It works by shining

the light on the paper being scanned and measuring the light that is

reflected back with the help of optical sensors. If the image being scanned is

page of text, then special optical character reading software is used. If page

contains pictures then special image editing software is used. Its types are

flatbed scanner, drum scanner and handheld scanner. Drum scanners are

expensive and gives the best performance. Handheld scanners are the least

expensive and perform the worst. Flatbed are the most popular ones.

v Barcode Reader : A barcode is a group of vertical bars randomly

generated by computer software with different thickness and spacing. It
consists of twelve digits, first six digits represents the product information
and second six represents manufacturer details. A barcode reader is a
photoelectric scanner that reads the barcodes printed on product wrappers.
It consists of a light source and light sensors translating optical impulses

into electrical pulses. These signals are used to extract the relevant
information from the database of computer to which the device is attached
to. This technology is widely used in super markets, warehouses, retails
stores and in libraries.

v Magnetic Character Recognition : MICR is a character

recognition system which uses a magnetic ink reader to recognize the

characters printed with specialized magnetic ink called toner. This

technology is used primarily by the banks to verify the legitimacy of the

cheques while transaction processing. MICR characters are printed on

documents are printed using a magnetic ink containing iron oxide. When

these characters are passed over the reader’s head, same specific pattern

will be formed in the reader’s head because of the magnetic field caused by

magnetic ink.

While OCR technology captures the image and recognizes the

characters, the MICR technology picks up the magnetic toner to draw the

pattern from document and recognize it.

A MICR device can operate at the speed of reading 2400 characters per

Audio Input Devices

Audio devices are the input peripherals used in the modern computer
system to capture sound and voice. It is mainly used for voice mail, video chat,
telephones, tape recorder etc. It enables the computer system to accept music,
speech or sound effects for recording and editing.

Microphone is the most widely used audio input device which captures the
sound as input for computer by converting the mechanical energy/waves of sound
into electrical energy. As we produce sound near microphone, sound card (ADC +
DAC), using its ADC will do the conversion.

Video Input Devices

Video input devices are input units used to capture the video (on-going
motion pictures) from the outside world along with the sound. The video card is
used to convert the analog video signals to digital form to store it in the computer
and vice versa.

v Digital Camera : A digital camera is a hand held portable device that

takes video or still photographs, or both, digitally by recording images via

electronic image sensors.

v Webcam : A web cam is a digital camera capable of downloading

images to a computer for transmission over the Internet or other network.

They are widely used for video conferencing. They are also used as security

cameras for CCTV systems.

Output Devices

An output device helps to give the final result from the CPU to the monitor,
speaker or printer. Generally, output device is classified into two types as
hardcopy output devices such as printer, plotter and softcopy output device such
as monitor, projector, speaker etc.

v Monitor : A monitor is a television like video display unit connected to the
computer system which produces the visible information in the form of text,
icons, pictures, videos and animation. Monitor screen is measured
diagonally in inches across the screen to find its size.

Types of monitors :
i. CRT (Cathode Ray Tube)
ii. LCD (Liquid Crystal Display)

iii. LED (Light Emitting Diode)

CRT Monitor :

A CRT monitor contains millions of tiny red, green and blue phosphor dots
(a synthetic shiny substance) that glow when struck by an electron beam. In the
electron gun, when cathode is heated, it produces stream of electrons. Electrons
are negative in charge. The anode in the electron gun is positive, so it attracts the
electrons pouring off the cathode. The screen is coated with phosphor dots that
glows making images when hit by the electron beam. By blending the red, green
and blue colored phosphor dots different images are generated by the CRT

Pixel : Picture elements are the tiny dots arranged together in rows and
columns to generate image.

Resolution : The number of pixel presented on the screen plotted
horizontally and vertically is called resolution.

For eg :
Ø Screen resolution 1024 x 768 means 1024 pixels across the screen

horizontally and 768 pixels down the screen vertically.
Ø Screen resolution 1080 p is 1920 x 1080 p
Ø 4K means 4 x 1080 p
Ø 720 p means 1280 x 720

v Speaker (Voice output devices) : It is a softcopy output device that

produces and amplifies the sound. It is connected to the sound card present

in the motherboard which converts the digital data into the analog (sound


v Printer : A printer is a hardcopy output device that produces text

and graphics on paper. The quality of printer depends on the following

factors such as color it produces, resolution, speed, memory etc. There are

two types of printers as :

a) Impact Printers
b) Non-impact Printers

Impact Printers : It is a printer that uses mechanical hammering device to
produce each character. Each hammer head is embossed with the shape of an
alphanumeric characters and symbols. The print head can move back and forth.
When any character is to be printed, the corresponding print head moves forward

and hits the ink soaked ribbon pushing it onto the paper leaving an image. The
most popular impact printers are drum printers and dot-matrix printers.

Non-Impact Printers : Non-impact printers forms the characters and images

without direct physical contact between printing mechanism and the paper. The

printing is done by spraying ink droplets, using thermal technology and using

laser beam. The most popular kinds of impact printers are ink jet printer and

laser printer.

Difference :

Impact Printer Non-impact Printer

• It prints characters by striking • It prints the characters and
print hammer against the inked images without striking the

ribbon. paper.

• It generates noise during • It does not generate noise during
printing. printing.

• It uses inked ribbon for printing. • It uses toner or cartridge for

• It normally uses continuous • It normally uses individual paper
paper sheet. sheet.

• It is comparatively slower and • It is comparatively fast and
cheaper. expensive.

• Its printing quality is low. • Its printing quality is high.

Types of Impact Printers :

v Drum Printers : A drum printer consist of a cylindrical drum on which

characters are embossed and print hammers which pushes the paper onto

the inked ribbon against the embossed characters. The drum rotates at the

very high speed and a character is printed by activating the appropriate

hammer. Drum printers can only print pre defined characters and it cannot

print images. They are also very noisy as it uses hammering technology. It

is capable of printing at a very high speed ranging from 125 to 3000 lines

per minute.

v Dot- Matrix Printers : It is an impact printer that produces text when

tiny pins on the print head strike the ink ribbon. It prints characters as per

the combination of dots. They have a matrix of pins on the print head which

forms the character. The print head moves back and forth on the paper.

There is an inked ribbon between the pins and the paper. When the pins

forming a particular pattern hits the inked ribbon onto the paper, with dots

characters are printed. Dot matrix printer can create 30 to 40 characters per


Types of Non-impact Printers :

v Ink Jet Printers : These printers print characters by spraying patterns
of ink on the paper out of cartridge or ink tank. The ink comes out from
nozzles having fine holes, from which a specially made ink is pumped out to
create various letters and shapes/images.

Software instructs the printer where to spray the ink, which
color and what quantity to use. Electric pulses are sent to the resistors
behind each nozzle. Vapor bubbles of ink are formed by the resistors when
heated and the ink is forced to the paper through nozzles.

v Laser Printers :

It is a type of printer that utilizes a laser beam to produce an image on
a drum. The light of laser alters the electrical charge on the drum wherever it
hits. The drum is then rolled through the container of toner, which is picked up
by the charged portions of the drum. Finally, the toner is transferred to the paper
through a combination of heat and pressure using rollers by fusing the toner
during the printing process.

v Plotter :
A plotter is a special printer that interprets the
commands from a computer to make high quality
drawings, maps, charts and other forms of
graphics using one or more automated pen. By
using point-to-point connection of lines and curves
different shapes are drawn by a plotter. It uses
vector graphics files to get drawing help. Plotter is
generally used by the engineers, architects and
graphics desingers.

Secondary Memory Devices

The secondary memory devices are the data storage units that supplements
the primary memory. It facilitates the storage of large volume of data on a more
permanent basis for future reference. Information may be erased from the
secondary media, but unlike primary media, the information does not disappear
when the power supply to the machine is terminated.

Ultimately all data stored on a computer is stored as a sequence of binary digits
i.e. strings of ones and zeros. Physically these zeros and ones are implemented
using wires with two different voltages, magnetic particles with two different
alignments and spots on an optical disk having two different optical properties.

Three main types of auxiliary storage media are :
1. Magnetic Tape
2. Magnetic Disk
3. Optical Disk
4. Flash Memory

1. Magnetic Tape :

Magnetic tapes are the sequential memory
devices which uses thin, magnetizable plastic film
usually of 50 to 2400 feet long. The magnetic tape
drive system is used to read and write data. When the
read/write head of the drive passes over the tape
ribbon, data can be read from or written to the tape.
It has very slow data access time as it is sequential,
which means to get to a particular point, all the
preceding points must be intervened.


The first magnetic tape was invented for recording sound by Fritz Pfleumer in
1928 in Germany.

2. Magnetic Disk :

A magnetic disk uses magnetization process
to write, re-write and access data. Magnetic
memory devices have storage surface coated with
magnetic material such as iron oxide which can be
magnetized using the magnetic field. The
orientation of magnetic field is used to represent
data. To store data on the magnetic disk the
read/write head passes over the surface of the
storage device generating the magnetic field which
will magnetise the magnetic molecules and arrange
the polarity as per the requirement and hence
stores data.

Data stored on a magnetic disk can be directly accessed, regardless of the
order in which the data was originally recorded. Because magnetic spots can be
read randomly, data retrieval is very quick.

The basic types of magnetic disks are hard disk, floppy disk, zip disk and super

Ø Hard Disk : Fixed hard disk is the “data center” of the PC. It is a non
volatile random access device for digital data. It features rotating rigid
platters on a motor-driven spindle within a protective enclosure. The
platters made up of aluminum are mounted on a stack on a common spindle.
On both sides of platter iron oxide is coated to make it magnetizable. Data
is magnetically read and written with the faster pace and greater capacity.

Ø Floppy Disk : Floppy disks are small,
removable, media storage devices that are
mostly used for transferring software
between computers. They record the data
onto a thin, circular magnetic film encased
in a flat, square plastic jacket. It was
originally created by IBM in 1967. Floppy
disk comes with three different sizes as 720
KB, 1.44 MB and 2.88 MB.

Floppy disks have largely been replaced with CD’s, DVD’s and flash drives.

Ø Zip Drive : Zip drive is a removable floppy

disk storage system capable of holding moderate

amount of computer information. This disk

comes with the built in program that could lock

the files for security.

3. Optical Disk : An optical disk is an electronic data storage device that can

be written to and read using a low powered laser beam. It can provide
tremendous storage capacities at a relatively cheaper cost. Data in the
optical disks is relatively unaffected by most environmental threats such as
power surges or magnetic disturbances. Hence, it provides high data

Ø CD-ROM and DVD-ROM : These are the read only memory which

means cannot be written over and can only be read. The data is stored as a

series of pits (equivalent to a binary value 1) and lands (equivalent to 0) in

the metallic optical layer. The pits are formed by a high-powered laser beam

etching the surface at the manufacturing stage. The pits and lands are read

by a low-powered laser beam. They are used to store music files, software,

computer games and reference software (such as encyclopedia).

Ø CD-R and DVD-R : The letter ‘R’ means the disk is recordable only once.

These disks use a thin layer of organic dye as the recording media. A laser
beam produces the heated spots and unheated spots. Reading these two
types of spots data is interpreted as 1s and 0s.

Ø CD-RW and DVD-RW : The ‘RW’ means that these disks are re-writable
media and can be written over several times. The recording layer uses a
special phase-changing metal alloy. The alloy can be changed between

crystalline and amorphous (non-crystalline) phases, thus changing its
reflectivity to light depending on laser beam power.

Ø Blu-ray Disk : Blu-ray Disk is a high density optical disk format for the
storage of digital media, including high definition video. The name Blu-ray
Disk is derived from the blue-violet laser used to read and write this type of
disk. Its each side can store 25 GB of digital content.

4. Flash Memory : Flash memory is non-volatile data storage and thus

capable of retaining it’s data even when it’s power source has been turned

off. Flash memory is small, lightweight, noiseless and very reliable.

Ø Pen drive : It is portable USB (Universal Serial Bus) flash memory

device that can be used to transfer audio, video and data files from one

computer to another computer. It consists of a small printed circuit board

encased in plastic or metal casing. The USB port is usually covered by a
removable cap. These flash drive vary in storage capacity (64 MB to 32 GB)
and are rewritable.

Ø SSD (Memory Card) : Memory card is an electronic flash memory data

storage device used for storing digital information such as text, pictures,

audio etc. for small, portable and remote computing devices like mobile

phones, digital cameras, video game consoles etc. They are called solid state

drive because they have no moving parts and therefore, are unlikely to suffer

mechanical difficulties.

System Unit Components

The system unit, also known as “tower” or “chassis” is the main part of a
desktop computer. The system unit includes the case that houses the internal
components of the computer system like motherboard, microprocessor, memory
units, expansion ports etc.

Ø Motherboard : Motherboard is the backbone of the computer system that
connects all parts of a computer together and allows them to communicate
with each other. It connects the CPU, memory units, video card, sound card
and other ports directly or via cables. It is large flat circuit board covered
with sockets, and other electronic parts, including a variety of chips.

Ø Microprocessor : Microprocessor is the power source of a modern

digital computer system. It is the computer processor on a microchip. It is a

very complex integrated circuit, containing millions of miniaturized

electronic components. A microprocessor consists of several different

sections : The ALU performs calculations and makes logical decisions; the

registers are special memory locations for holding temporary information;

the control unit directs and co-ordinates the activities of the entire

computer, buses carry digital information through out the chip and the

computer; and local memory supports on-chip computation. More complex

microprocessors often contain cache memory to speed up access to external

data storage devices.

Ø Primary Memory : Primary memory is a computer memory that is
directly accessible to the CPU of a computer system. It holds the data and
programs before processing, between processing steps, and after processing;
prior to releasing data as output. There are two types of memory chips as
RAM and ROM.

RAM is a high speed memory that holds a copy of the operating system,
currently executing programs and other information being processed.

ROM is a semiconductor based memory that contains a set of start-up
instructions, checks for hardware devices and checks for an operating
system on the computer’s disk drives.

Ø Expansion Port : Expansion port is any connector that passes data in

and out of a computer or peripheral device. All the peripheral devices are

attached to the computer system to enhance its capabilities using expansion

ports and slots. Different ports in computer providing interface are serial

port, parallel port, AGP, PCI slots, USB ports and FireWire ports.

Serial ports are used to connect a mouse, keyboard, modem, and many

other devices to the system unit. Parallel ports are used to connect external
devices such as printers and some external storage devices. Accelerated Graphics
Ports (AGP) are used to connect monitors. USB ports are faster and one USB port
can connect up to 127 different devices with a single connector. FireWire or IEEE
ports are used to connect high speed printers and even video cameras to the
system unit.

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