Vedanta Let's Log in Computer Science Book - 9.indd

Approved by the Government of Nepal, Ministry of Education, Science and Technology, Curriculum
Development Centre, Sanothimi, Bhaktapur as an Additional Learning Material

vedanta

Computer Science

Book

Authors:

Sunil Kumar Gharti Sushil Upreti

vedanta

Vedanta Publication (P) Ltd.
jb] fGt klAns;] g k|f= ln=

Vanasthali, Kathmandu, Nepal
+977-01-4982404, 01-4962082
[email protected]
www.vedantapublication.com.np

vedanta Book

Let's Log in

Computer Science

All rights reserved. No part of this publication may be reproduced, copied or
transmitted in any way, without the prior written permission of the publisher.

Authors: Sushil Upreti
Sunil Kumar Gharti

© Vedanta Publication (P.) Ltd.

Design: Manoz Manohar
First Edition: BS 2077 (2020 AD)
Second Edition: BS 2078 (2021 AD)

Printed in Nepal

Published by:

Vedanta Publication (P) Ltd.
j]bfGt klAns];g kf| = ln=

Vanasthali, Kathmandu, Nepal
+977-01-4982404, 01-4962082
[email protected]
www.vedantapublication.com.np

Preface

This is the age of information. Information Technology
has undoubtedly invaded all walks of life to such an extent
that computer and information literacy has become the
fundamental part of our daily activities. Computer Science
is now an essential addition to the school curriculum at all
levels.

Vedanta Let's Log in (A course in Computer Science)
is a series of ten books on Computer Science for basic
and secondary level students, designed for the need of
new generation to help acquire knowledge on the theory,
application and programming aspects of computing. This
series is based on the new syllabus of Computer Science,
designed and approved as per the curriculum prescribed
by Curriculum Development Center, Ministry of Education,
Government of Nepal.

The series covers the history of computer, its accessories,
applications and programming in LOGO and QBASIC in
a step-by-step and graded manner following logical and
scienti ic approach. Concept of graphic and web design is
also illustrated with many practical examples. This series not
only assists the students and the teachers in the class but also
incorporates latest information and developments in IT with
the present need of the students in Nepal. It also provides
other enthusiasts and learners with the skill and knowledge
to cope up with the growing demand of IT skills in market
and daily life.

We earnestly hope that the students would ind the journey
through this series an enjoyable experience and gain a sound
working knowledge on the basic aspects of computing and
information technology.

As far as possible, we have sincerely put in our efforts to
make the book error free. However, there is always scope
for improvement. Constructive criticism and feedback are
always welcome.

Authors

Content

S.N. Lesson Pg. No.

1. Group A : Computer Fundamentals 5

1.1 Introduction 6

1.2 Types of Computer 17

1.3 Computer System 26

1.4 Computer Hardware 36

1.5 Computer Software 61

2. Group B : Working with Graphics 81

2.1 Different Graphics Format 83

2.2 Graphics for Web 84

2.3 Image Size, Resolution 87

2.4 Graphics Editing 89

3. Group C : Internet and Web Technology 110

3.1 Internet Technology 111

3.2 Hyper Text Markup Language (HTML) 123

3.3 Cascading Style Sheet (CSS) 161

4. Group D : Computer Programming 186

4.1 General Concept 187

4.2 Programming in QBASIC

4.2.1 : Introduction to QBASIC 202

4.2.2 : Data Types in QBASIC 212

4.2.3 : Operators, Operands, and Expressions 220

4.2.4 : Programming in QBASIC 228

4.2.5 : Program Flow and Control Structures 244

4.2.6 : Library Functions 272

4.2.7 : Array 292

Abbreviation 299

Model Question ( Theory) 301

Model Question ( Practical) 304

Vedanta Let’s Log in Computer Science | Book 9

Group

A

5 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

Unit

1.1

The word “computer” comes from the word “compute,” which means “to
calculate.” Hence, people usually consider a computer to be a calculating device
that can perform arithmetic operations at high speed.
Computer is now affecting every sphere of human activity and leading to many
changes. It has been used in almost all the fields, from home to schools, colleges,
supermarkets, hospitals, hotels, research centers, robotics, industry, government
offices, scientific research, law, entertainment, airlines, traffic control, and even in
arts like music and painting. It has brought enormous changes in the world.
The modern world of advanced technology could not have been established
without the development of the computer technology. Different types and sizes
of computers find uses throughout society in the storage and handling of data,
from secret government files to banking transactions, private household accounts.
Computers have opened up a new era in manufacturing through the techniques
of automation, and they have enhanced modern communication systems. They
are essential tools in almost every field of research and applied technology, from
constructing models of the universe to producing tomorrow’s weather forecasts,
and their use has, in itself, opened up new areas of speculation. Database services
and computer networks make available a great variety of information sources. The
same advanced techniques also make possible invasions of personal and business
privacy. Computer crime has become one of the many risks that are part of the
price of modern technology.

What is a Computer?

A computer is an electronic device, which processes raw data (unprocessed facts)
fed to it and gives out the meaningful information through its output device
after the input data is processed by its processor. A computer consists of following
components: input device through which data are fed to it, central processing
unit (CPU) where the data get processed, memory to store, at least temporarily,

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 6

Vedanta Let’s Log in Computer Science | Book 9

data and programs, the output device that lets you see what the computer has
accomplished and mass storage device which allows a computer permanently
keep large amounts of data.

Printer Monitor Webcam Central Processing Unit
(Output) (Output) (Input) (CPU Casing)

CD/DVD
Drive

Router Audio Jack
Input/Output
Speaker
(Output) Power
Button

Microphone
(Input)

Headphones Keyboard USB Drive Mouse
(Output) (Input) (Input)

Computer System

It is also a machine that can choose, copy, move, compare, and perform other non
arithmetic operations on the alphabetic, numeric, and other symbols like name,
location, gender, cell number, e-mail id, etc. The computer manipulates these
symbols in the desired way by following an “intellectual map” called a program.
It is a fast and accurate electronic symbol (or data) manipulating system that is
designed to automatically accept, raw data, process them, and produce output
results under the direction of a step-by-step stored program of instructions.

Characteristics of Computer

Computer is not just adding machines: it is capable of doing complex activities and
operations, also. The power and usefulness of this popular tool are mainly due to
its following characteristics:

7 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

a. Accuracy

Accuracy of a computer is consistently high and the degree of its accuracy
depends upon its design. The circuits in a computer have no mechanical parts
to wear and malfunction. A computer performs every calculation with the
same accuracy. In most cases, the errors appear due to the human rather than
technological weaknesses. For example, errors may occur due to imprecise
thinking by a programmer (a person who writes instructions for a computer to
solve a particular problem) or incorrect input data. We often refer to computer
errors caused due to incorrect input data or unreliable programs as garbage-in-
garbage-out (GIGO)

b. Automatic

Computers are automatic machines because once started on a job, they
carry out the job (normally without any human assistance) until it is completed.
However, computers being machines cannot start themselves: They cannot go out
and find their own problems and solutions. We need to instruct a computer using
coded instructions that specify exactly how it does a particular job.

c. Diligence

The ability of computer to perform a work repeatedly without getting tired and
bored is called diligence. Unlike human beings, a computer is free from monotony,
tiredness, and lack of concentration. It can continuously work for hours without
creating any error and without grumbling.

d. Speed

A computer is a very fast device. It can perform in a few seconds, the amount
of work that a human being can do in an entire year – if he/she worked day and
night and did nothing else. In other word, a computer can do in a few minutes what
would take a human being the entire lifetime.
While talking about the speed of a computer, we do not talk in terms of seconds
or even milliseconds (10-3) but in terms of microseconds (10-6), nanoseconds (10-
9), picoseconds (10-12), and even Femtosecond (fs). As the power of the computer
increases, the speed also increases. For example, supercomputers can operate
at speeds measured in nanoseconds and even picoseconds – one thousand to one
million times faster than microcomputers.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 8

Vedanta Let’s Log in Computer Science | Book 9

Unit of time Part of second Power Meaning

of 10

Millisecond (ms) 1/1000 10-3 One thousandth of a second
Microsecond (Ps) 1/1000000
Nanosecond (Ks) 1/1000000000 10-6 One millionth of a second
Picosecond (ps) 1/1000000000000
Femtosecond (fs) 1/1,000,000,000,000,000 10-9 One billionth of a second

10-12 One trillionth of a second

10-15 One quadrillionth of second

e. Storage (Power of Remembering)

As human beings acquire new knowledge, their brain subconsciously selects
what it feels to be important and worth retaining in memory. The brain relegates
unimportant details to back of mind or just forgets them. This is not the case with
computers. A computer can store and recall any amount of information because of
its secondary storage capability. It can retain a piece of information as long as a
user desires and the user can recall the information whenever required. Even after
several years, a user can recall exactly the same information that she had stored in
the computer several years ago. Computer forgets or loses certain information only
when a user asks it to do so. Hence, it is entirely up to the user to make a computer
retain or forget some information.

f. Versatility

Computers are very versatile machines. They can perform activities ranging
from simple calculations to performing complex CAD modelling and simulation to
navigating missiles and satellites. They are capable of performing almost any task,
if the task can be reduced to a finite series of logical steps.

g. Absence of Intelligence

A computer is not a magical device. It possesses no intelligence of its own. It
requires instruction to do certain things in sequence. Hence, only a user determines
what tasks a computer performs. A computer cannot take its own decision in this
regard.

h. Absence of Feelings

Computers are devoid of emotions. They have no feelings and no instincts
because they are machines. Although men have succeeded in building a memory
for computer, but no computer possesses the equivalent of a human heart and

9 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9
soul. Based on our feelings, taste, knowledge, and experience, we often make
certain judgements in our day-to-day life, whereas computers cannot make such
judgements on their own. They make judgements based on the instructions given
to them in the form of programs that are written by us (human beings).

Application Areas of Computer

Computers have changed the way we work, in every profession. Therefore, it is
only natural that the role of computers in society has gained a lot of importance
in recent years. Computers play a vital role in every field. They aid industrial
processes; they find application in medicine, communication and games; they are
the reason why software industries developed and flourished; and they play an
important role in education. Considering the use of computer technology in almost
every sphere of life, it is important for everyone to have at least the basic knowledge
of using computers.

a. Education

Computer technology has a deep impact on the education sector. With
the help of computer imparting education has become easier and much more
interesting than ever before. Teaching computer plays a key role in the modern
education system. Computers assist teachers in teaching their students easily and
quickly. Students can search for the concepts or things which they wish to know
by referring to relevant websites. Internet is an ocean of information and surfing
it daily increases the knowledge of
these students greatly. Such form of
receiving education is considered to
be more effective than only learning
from textbooks prescribed by the
authorities. Computers facilitate
teachers effective presentation of
information in while delivering
lectures. Computers facilitate audio-
visual representation of information,
thus making the process of learning
interactive and interesting. The Education

students can be shown charts, diagrams, and figures while teaching practic oriented
subjects. Many educational multimedia CDs like Microsoft Encarta, Encyclopedia,
Computer Based Training (CBT), Computer Aided Education (CAE), Computer
Based Learning (CBL) courses, etc. are used by students and teachers to learn and
teach different things.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 10

Vedanta Let’s Log in Computer Science | Book 9

b. Science Science

Computers have played an important role in
the field of science. Computers are used by scientists
to develop theories, analyze, classify, collect, and
test the data, and exchange information around
the world. Computers are used to generate detailed
studies of how earthquakes affect buildings or how
pollution affects weather pattern. Computers are
being used for research in space. They are also used
in the design and operation of man-made satellites,
space exploration vehicles, rockets, training of
astronauts and investigation in medical science to
find out diseases and medicines.

c. Business

Computer is known to be an effective
tool for business. All the businesses want
to use computer for a variety of reasons:
employee training, sales presentations,
educating consumers, communication
and interaction, etc. To promote the
business, new product and the type of
service your business offers, multimedia
is used for preparing effective and Business

interesting advertisements. High-quality multimedia such as a website, brochure,
video, advertising, instructional manual or animated explanation can be used in
business to provide the information of quality and price of product.

d. Banking

Computers have played a very important role in
the growth and improvement of banking and finance
sectors. They are used for various purposes such
as cheque verification, online enquiry of customer’s
balance, calculating interests, printing customer
statements, and keeping the records of employees
in the bank. Banks have installed Automated Teller
Machine (ATM) for customer services twenty-four Banking

hours of the day in order to deposit and withdraw money. Computers help to get
connected to different branches of bank through network for sharing information
and inter branch transaction within very short period of time.

11 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

e. Communication Communication

Computers have played an important
role in the field of communication. E-mail
and Internet Relay Chat (IRC) are facilities
supported by computers to send and receive
messages or instant messages from one
place to another. Internet telephony is also
important service of computer through which
people can talk from one place to another
easily. Computer communication is one of the
cheapest, reliable, and fastest communication
media.

f. Game Game

One of the most exciting applications of
computer is game. Actually the first application of
computer was in the field of entertainment and that
too was in the video game industry. The integrated
audio and video effects make various types of games
more entertaining. Multimedia technology makes
possible to keep interactive and exciting sound,
graphics or animation in the games to provide
entertainment to the player. Several developers
have used graphics, sound, and animation of
multimedia to create variety of games. Nowadays,
the live internet pay to play gaming with multiple
players has become popular.

g. Manufacturing Manufacturing

The application of computer in various
functional areas of manufacturing such
as marketing, design, and engineering,
production and distribution has tremendous
potential. Computer can also be used
as an open development framework for
manufacturing applications, especially in
Computer Aided Designing (CAD), Computer
Aided Engineering (CAE), and Computer
Aided Manufacturing (CAM) by providing
users with tools to re-engineer and integrate

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 12

Vedanta Let’s Log in Computer Science | Book 9

product and process information. In factories, computers and interactive video
have been widely used for designing and planning the production.

h. Health Care

Pay a visit to your family doctor or the local
hospital, and you’ll find yourself surrounded by
computerized equipment of all kinds. Computers,
in fact, are making health care more efficient
and accurate while helping providers bring down
costs. Many different health care procedures now
involve computers, from ultrasound and magnetic
resonance imaging, to laser eye surgery and fetal
monitoring. Surgeons now can use robotic surgical
devices to perform delicate operations, and even
to conduct surgeries remotely. New virtual-reality Health Care

technologies are being used to train new surgeons in cutting-edge techniques,
without cutting an actual patient. But not all medical computers are so high-tech.
Clinics and hospitals use standard computers to manage schedules, maintain
patient records, and perform billings. Many transactions between physicians,
insurance companies, and pharmacies are conducted through computers, saving
health care workers time to devote to more important tasks.

i. Journalism Journalism

Newspaper companies all over are also
trying to embrace the new experience by
implementing computer practices in their work.
News reporting is not limited to traditional media
outlets. Freelance journalists can make use of
different new media to produce multimedia pieces
for their news stories. It engages global audiences
and tells stories with technology, which develops
new communication techniques for both media
producers and consumers.

j. Household and Personal Use

A computer is used in home appliances like micro wave oven, refrigerator,
washing machine, vehicle, home security as well as various devices, etc.

13 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

POINTS TO REMEMBER

The word “Computer” is derived from Latin word “Compute” which means to calculate.
A computer is an electronic device that processes data, converting it into information

that is useful to people.
Data is a collection of facts that is entered as input the computer.
Information is the output that is received after the data is processed.
The speed of computer is measured in Mega Hertz (MHz), Giga Hertz (GHz).
A large amount of data stored in the secondary storage like hard disk, pen drive, CD/

DVD, etc. are used to hold data and programs permanently for future use.
Computer and its technology are used in areas of education and agriculture for their

development.
A computer is used in scanning and diagnosing various diseases by CT scans, ultra

sounds, ECG, etc.
Computer technology is playing an ever-growing role in schools, where students are

being taught computer skills at younger ages.
Computers are involved in nearly every aspect of the health care field.
The home computer can be used in learning, playing games, listening to music or

watching movies.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 14

Vedanta Let’s Log in Computer Science | Book 9

Exercise

1. Fill in the blanks.
a. The word “computer” comes from the word……….., which means, ………….
b. A computer is an ………….device.
c. Computer accepts the data from user through …….……. devices.
d. In business, ICT is often categorized into …………….of product.

2. Match the following: Group B
Group A i. Huge amount of data can be stored
ii. Takes only few seconds for calculations
a. Speed iii. Does not have emotion, taste and experience.
b. Versatile iv. Use of computer is not limited to any single task
c. Diligence v. Computers gives correct answer
d. Storage vi. Never get tired or bored of doing tasks
e. Accuracy vii. Error due to wrong input
f. No Feeling

3. Give full forms of the following abbreviations:

a. IBM b. GB c. KB d. AI e. MHz f. GIGO g. ICT

4. Write short notes on the following: b. Application of computer
a. ICT d. Computer in banking Sector
c. Scientific Research f. Speed
e. Storage

5. Answer the following questions.
a. What is computer? List any two characteristics of computer.
b. List and explain some important characteristics of computer.
c. What is garbage-in-garbage-out?

15 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

d. Write in short use of computer in education.
e. Why is computer known as versatile machine? Explain.
f. Why is computer called diligence machine?
g. Write the use of computer in education field.
h. Write any four uses of computer.
i. Define ICT. How has it made the world smaller?

Activities

1. During the course of a normal day, keep a list of your encounters with computer of
various kinds. Your list should show the place and time of the encounter, the type
of interaction you had with the technology, and the results of that interaction. Share
your list with the class.

2. Describe your experience with computers so far. Have you worked with (or played
with) computers before? If so, why? Has your past experience with computers
influenced your decision to study them?

3. Draw on chart paper “Computer and its parts” and paste in your classroom.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 16

Vedanta Let’s Log in Computer Science | Book 9

Unit

1.2

Introduction

Computers are classified into various types. This classification is based on their
different attributes. Since the application areas of computers are not limited.
Computers used in different sectors are of different types. Here we discuss them
on the basis of work.

TYPES OF COMPUTER

On the Basis of Work

Analog Computer Digital Computer Hybrid Computer

1. Analog Computer Analog-computer

Analog Computers work on continuous
signals. They are based on continuous
changing values or voltage levels. For
example, thermometer does not perform any
calculations but measures the temperature of
the body by comparing the relative expansion
of mercury. The analogue computer is a more
sophisticated electronic or hydraulic device
that is designed to handle input in terms of
voltage levels or hydraulic pressures, rather
than numerical data. They are mainly
used to control scientific equipment for
engineering purposes because they deal
with quantities that vary constantly. They
give only approximate results.

17 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

2. Digital Computer Digital Computer

Everything that a digital computer does is
based on one operation: the ability to determine
whether a switch, or “gate”, is opened or closed.
That is, the computer can recognize only two states
in any of its microscopic circuits: on or off, high
voltage or low voltage, or in the case of numbers,
0 or 1. So, the basic principle of these computers is
either present or absence of electrical pulses in the
signals. Examples of these computers are IBM PC,
or Apple Macintosh (PC you used in your LAB)

a. Microcomputers

The most familiar kind of computers are the microcomputers. These are the
smallest computer systems on the basis of the size. These computers are called
micro because microprocessor is used as a memory device and they are very
small. In the past, microcomputers have been considered to be of two types:
personal computers and workstations.

i. Personal Computers (PCs)

It is a computer specifically designed Personal Computer
for the use by one person at a time, equipped
with its own central processing unit, memory
unit, operating system, keyboard, display,
hard drive, a CD/DVD drive, as well as
other peripherals when needed. Examples
of personal computer are Acer’s, DELL,
COMPAQ, Mercantile PC, etc.

ii. Workstations

A workstation is a high-
performance computer designed to
meet computing needs for graphics
applications such as computer
aided design (CAD), computer-
aided engineering (CAE), or
scientific applications. It has
greater processing power, large Workstations

storage, and better graphics display facility than what normal PCs provide.
Workstations generally run the UNIX operating system or its variants such

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 18

Vedanta Let’s Log in Computer Science | Book 9

as AIX, Solaris, and HP-UX. Workstations generally cost from a few lakhs to
tens of lakhs of rupees depending on the configuration. Some manufactures
of workstations are Sun Microsystems, IBM, DEC
and Hewlett-Packard (HP).

b. Portable Computers

Portable computers mainly meant for use by people
who need computing resource wherever they go. These
types of computers are becoming smaller and yet more
powerful. The first portable DOS-based computers were
known as “luggables” because they were definitely not
easy to carry. Later models fall into these categories:

i. Laptops / Notebooks Portable computer

Laptops more frequently called notebook computers may be either AC-
powered, battery-powered, or both. It’s small enough to be use in an airplane
seat or on one's lap. Many models of laptops can be “docked” on a docking
station to take advantages of the big monitor,
storage space, and other peripherals such as a
printer. They are powerful enough to run major
OS and applications, including MS-Windows,
LINUX, and all popular business applications
programs. Since laptops are meant to be mobile
and used from anywhere, their design enables
them to establish wireless connectivity with other
stationary computer using WiFi and Bluetooth. Laptop / Notebook

ii. Tablet PC

A tablet PC is a miniaturized laptop. It Tablet PC
usually provides all features of a laptop with
following enhancements. Lightweight, Screen
flip, Handwriting recognition, Voice recognition,
Special design for tablet use are some of the
features available in it.
iii. Palmtop

A very small battery powered portable
computer that you can hold in one hand, often
weighing about a pound. Palmtop computers have
small screens of 8 lines by 40 characters and tiny
keyboards.

Palmtop

19 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

iv. PDA/Pocket PC

Personal Digital Assistant (PDA) was initially introduced as a Personal
Information Manager (PIM) device. Its features include contact list, calendar,
task list, e-mail, pocket dictionary, spreadsheet, word processing, PDF format,
and other applications easy to use. It fits into a pocket.

Newer PDAs also pack network capability PDA/Pocket PC
using WiFi, Bluetooth, etc. Several PDAs also
provide GSM/GPRS (Global System for Mobile
Communications/General Packet Radio Service)
service connectivity and thus can be used as cell
phone. It comes with several options of OS ranging
from Ms-Windows Mobile Edition, PalmOS,
SymbianOS, Linux, Blackberry OS, etc. An
Example of PDA is Apple’s Newton, Casio, Sony,
Sharp, Tandy, Toshiba, AT&T, etc.

3. Hybrid Computer Hybrid-computer

Hybrid means combination or cross link of
two or more types. It is a combination of both
analog and digital signals. A Hybrid-computer
system can perform the works done with analog
computers as well as with digital computers. It
can process both continuous and discrete data.
These computers are used for special purpose.
These types of computer are used in jet planes,
scientific research, etc.

4. Minicomputers

Minicomputers, also known as mid range
computers are centrally located CPU which is
connected with more than 50 terminals. It works
on Distributed Data Processing (DDP). The
processing power is decentralized or distributed
across different terminals in such computer.

Example of such computer is the Client/Server
model. In this end users can process at their own
microcomputers. They can also access and share Minicomputer

the resources of the centralized server database and use them. One of the popular
minicomputer systems is the VAX.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 20

Vedanta Let’s Log in Computer Science | Book 9

5. Mainframe

Mainframe computers can process several million-
program instructions per second. Large organizations rely
on these room-size systems to handle large programs with
lots of data. It can support more than 100 terminals.
Mainframes are mainly used by insurance companies,
banks, airline, and railway reservation systems, etc.
Examples of these computers are: IBM 1401, IBM S/390,
ICL 2950/10.

6. Supercomputer Mainframe

Supercomputers are the most Supercomputer
powerful and expensive computers
available at any given time. They
are used primarily for processing
complex scientific applications that
require enormous processing power.
Supercomputers use multiprocessing
and parallel processing technologies
to solve complex problems faster. Most
supercomputers are used by government
agencies.

Example of supercomputers applications are weather forecasting, oil exploration,
weapons research, large-scale simulation, aerodynamic designs and complex
structural engineering problems. Major vendors of supercomputers are Cray
Research Y-MP/C90, IBM, Fujitsu, Intel, Piz Daint, Tianhe-z, Titan, Seq voie, Cori,
ETA-10. Nowadays, the most powerful supercomputer is Sunway Taihulight from
National Super Computing Centre, Wuxi, China.

21 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

POINTS TO REMEMBER

Based on the operating principles, computers can be classified into Analog Computers,
Digital Computers and Hybrid Computers.

Analog Computers can measure continuously changing quantities such as voltage,
pressure, temperature length height, etc.

Digital Computers can perform many tasks according to user requirements.

Hybrid Computers are the special purpose computers that combine the best features
of both analog and digital computers.

On the basis of size, digital computers are classified into four types. They are Micro-
computer, Minicomputer, Mainframe computer, and Super computer.

The first microcomputer was IBM-PC which designed by IBM (International Business
Machine) company.

A microcomputer is a small, single-user computer based on a microprocessor.

The computers commonly used today are all digital computers.

The terms personal computer (PC) and microcomputer can be refer to any computer
meant for use by a single person.

Minicomputer is more powerful and expensive than Micro-computer.

Mainframe computers are multi-user and multi processor computers that support
more than 200 of PC.

Mainframes, minicomputers, and supercomputers are commonly used by
organizations and support the computing needs of many users.

Supercomputer is an extremely fast computer that can perform hundreds of millions
of instructions per second. They have a large main memory.

Applications of supercomputers are weather forecasting and other scientific
computing.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 22

Vedanta Let’s Log in Computer Science | Book 9

Exercise

1. Fill in the blanks.

a. Apple’s Newton is a ……………

b. ……………. has greater processing power, large storage, and better graphics display
facility then normal PC.

c. The first portable DOS-based computers were known as………….

d. Workstations generally run the …………O/S.

e. Many models of laptops can be …..on a ……….station.

f. Laptops/Notebooks establish wireless connectivity with other station using .................
and .................

g. Palmtop computers have small screens of ….......... lines by ..............… characters,
and tiny keyboards.

h. Minicomputers is connected with more than ................. terminals.

i. Supercomputers use ................. and ................. technologies.

j. VAX is a ................. computer.

2. Give full forms of the following abbreviations:

a. IBM PC b. DVD c. PDA d. PIM
h. PDF
e. CAD f. CAE g. HP i. DDP

3. Choose the best answer:

a. Cray Y-MP/C90 is a

i. Micro-computer ii. Laptop iii. Mainframe iv. Super computer

b. DDP stands for

i. Distributed Double Processing ii. Double Decimal Processing

iii. Distributed Data Programming iv. Distributed Data Processing

c. Which of the following is a portable computer?

i. Laptops ii. Tablet Pc

iii. PDAs iv. All of the above

23 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

d. IBM S/390 is a

i. Micro-computer ii. Laptop iii. Mainframe iv. Super computer

e. Personal computers are also called……….

i. mini computers ii. Micro-computers

iii. super computers iv. Maxi computers

f. Notebook PCs fall into a category of devices called …………

i. mobile computers ii. small computers

iii. handheld computers iv. Mini computers

g. Some notebook systems can be plugged into one of these devices, which give the
computer additional features.

i. port station ii. network station

iii. workstation iv. docking station

h. Which is the most powerful type of computers?

i. Micro-computer ii. Mini computer

iii. Mainframe computer iv. Super computer

4. Answer the following questions.

a. On what basis are computers classified today? What are major types of computers
there based on this classification scheme?

b. Define Hybrid Computer with its used.
c. What are differences between analogue and digital computers?
d. What are the different types of portable computers?
e. Why is a laptop personal computer?
f. Differentiate between general-purpose computers and special purpose computers.
g. What is a palmtop?
h. Notebook computers can be used even while traveling in a bus, train or airplane.

Discuss.
i. What is a personal computer? What are its main uses?
j. List the major differences between a PC and workstation.
k. Write in short about mainframe system.
l. What are the supercomputers and where are they used?

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 24

Vedanta Let’s Log in Computer Science | Book 9

Activities

1. What type of computer system do you use in your school lab? How much can you
tell about the system by looking at it? List as much information as you can about the
computer. Is it a desktop or tower mode? What brand is it?

2. Draw on chart paper “Types of computer on the basis of working principle” and
paste in your classroom.

RESEARCH AND REPORT

1. Using your own choice of resources (such as the internet, books, magazines, and
newspaper articles), research and write a short paper discussing on one of the
following topics:
The world’s smallest computer.
The use of supercomputers in mapping the human genome.

2. Prepare a presentation about the use and purpose of hybrid and supercomputer in
different sectors, and present to your class as group work.

25 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

Unit

1.3

Introduction

You might have observed that we have been referring to a computer as a system.
What can be the reason behind this? To know the answer, let us first understand
the definition of a system. A system is a group of integrated parts: when they
work together, they have a common purpose of achieving some objective(s). Since
a computer comprises of integrated components (Input unit, Output unit, Storage
unit, and CPU) that work together to perform the steps called for in a program, it
is a system.
Even though the size, shape, performance, reliability, and the cost of computers
have been changing over the years, the basic logical structure, as proposed by
John Von Neumann (concept of a stored program), has not changed. No
matter what shape and size of computer we are talking about, all computer systems
perform the following basic operations for converting raw input and data into the
useful information, presenting it to a user:
1. Inputting

Process of entering data and instructions into a computer system.
2. Storing

Saving data and instructions to make them readily available for initial or
additional processing as and when required.
3. Processing
Performing arithmetic or logical operations on data to convert them into
useful information.
4. Outputting
Process of producing useful information or results for a user, such hard copy
or soft copy.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 26

Vedanta Let’s Log in Computer Science | Book 9

5. Controlling
Directing the manner and sequence in which the above operations are
performed.
The Internal architecture of computers differs from one system model to

another. However, basic organization remains same for all computer systems.
Figure 1.1 shows a block diagram of a basic computer organization. It displays the
major building blocks (functional units) of a digital computer system. These units
correspond to the basic operations performed by all computer systems. Functions
of each of these units are described below.

Input Unit (Program or Secondary Storage (Information / Output Unit
Data) Primary Storage Results)

Control Unit Indicates flow or
Arithmetic Logic Unit instructions and data

Indicates the control
exercised by the control unit

1.1 Basic Organization of a computer system

Input Unit

The input unit that links a computer with its external environment performs
this task. This is the process of entering data and programs into the computer
system. An input device converts input data and instructions into a suitable binary
form which can be accepted by the computer. The commonly used input device is
a keyboard. A number of input devices which do not require typing for inputting
information such as mouse, lightpen, graphic tablet, joystick, track ball,

27 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9
touch screen, etc. have also been developed. In recent days voice input systems
have also been developed and microphone is used for that purpose.

Mouse Microphone Joystick Keyboard

Different Input devices

Central Processing Unit (CPU) Central Processing Unit

The Central Processing Unit (CPU)
is the brain of the computer. It includes
three major components MU, CU, and
ALU. It is the ‘compute’ in computer.
Modern CPU’s are called ‘integrated
chips’. The idea of an integrated chip is
that several processing components are
integrated into a single piece of silicon.
The CPU is composed of thousands (and
soon billions) of transistors.

A CPU usually contains an execution core with two or more pipelines, a data
and address bus, a dedicated arithmetic logic unit (ALU, also called the math
co-processor), and in some cases special high-speed memory for caching program
instructions from RAM. The speed of the CPU is measured in Hertz, Mega Hertz
(MHz), and Giga Hertz (GHz). These are also called CPU clock rate or CPU clock
speed. Nowadays, CPU speed is measured in Gigahertz (GHz).

The most advanced processors available are 64-bit processors. Intel has released,
dual core, quad core, six core, and eight core versions for home computing 64-bit
chips as has AMD. Some renounced processor manufacturers are Intel, IBM,
Cyrix and Advanced Micro Devices (AMD).

Control Unit (CU)

The control unit is the circuitry that controls the flow of information through the
processor and coordinates the activities of the other units within it. It controls the
sequence of actions by the program and input / output operations. It is the nerve

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 28

Vedanta Let’s Log in Computer Science | Book 9

center of the CPU. In a way, it is the “brain within the brain,” as it controls
what happens inside the processor, which in turn controls the rest of the PC. This
unit does a number of Supervisory functions:

It directs the flow of the INPUT from the Input Device to the primary memory.
Accordingly, it directs the flow of the raw data to the ALU to be processed.
It interprets the instructions in the program.
It then redirects the processed data from the ALU to the memory.
Finally it directs the flow of the meaningful information from the memory to
the output Device.

Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit, ALU is one of the many components within a computer
processor. The ALU performs mathematical, logical, and decision operations in a
computer. It is the last processing performed by the processor. Once the necessary
information by the ALU has been processed, it is be sent to the computer memory.
In some computer processors, the ALU is divided into two separate parts: the
AU and the LU. In this case, the AU performs the arithmetic operations and the
LU performs the logical operations. However, almost all ALUs are designed to
perform the four basic arithmetic operations (add +, subtract -, multiply *, and
divide /) and logical operations or comparisons such as, AND, OR, NOT, greater
than, less than, greater than equal to , less than equal to, not equal to, and equal
to (>, <, >= ,<= ,<> , =).

MU (Memory Unit- Register Array)

Memory unit is also a part of CPU but not the part of main memory that stores
currently executing task. It is located inside the microprocessor. It has very limited
storage. It is used to store very active data and instructions temporarily during
processing.

Memory

Memory is the workspace for computer’s processor. It is built within the computer
that stores the unprocessed and processed data as well as the program instructions.
It is immediate access memory.
We often call memory RAM i.e. Random Access Memory. The main memory is
called RAM because we can randomly and quickly access any location in the

29 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

memory. It consists of a limited capacity and temporary nature because the data
and programs remain there only as long as the computer has electrical power or is
not reset. The standard Base Memory is 640KB. It can be enhanced upto 1 GB,
2 GB, 4GB, 8GB depending on need of the software and user.

It has many small storage areas. Each
one is assigned an address – a built
–in and unique number that identifies
the location. Like a mailbox, a storage
location can hold either a data item
or an instruction, and its identifying
number remains the same regardless
of its contents. Each address holds one
alphanumeric character. Each character
is represented in a storage location by a RAM

string of adjacent binary numbers (0s and 1s) that are treated as binary digits or
bits. A group of 8 bits is called a byte.

Types of RAM

a. DRAM (Dynamic RAM)

It stands for Dynamic RAM. It is the type of memory in modern
computer. The main advantage of DRAM is that it is dense, meaning that
we can pack a lot of bits into a very small chip. Also, it is very cheaper and
affordable for large amount of memory.

b. SRAM (Static RAM)

SRAM chips require very little current to keep their storage capacities
fresh. The RAMs are relatively expensive; however, they are generally found
only in special applications such as laptop computers and pocket calculators.
ROM: Read-Only Memory, or ROM is a non-volatile memory chip in which data
is stored permanently. It cannot be altered by usual programs. Data stored in a
ROM chip can only be read and used: they cannot be changed. This is the reason
why it is called read-only memory. ROMs are used by computer manufacturers to
store micro-programs (the software that boots the system, also called “Firmware”)
so that they cannot be modified by the users. There are three types of ROM: PROM
(Programmable Read-Only Memory), EPROM (Erasable PROM), and EEPROM
(Electrically Erasable PROM).

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 30

Vedanta Let’s Log in Computer Science | Book 9

The functions of the memory unit are
It stores intermediate results of processing.
It stores all the data and the instructions required for processing.
It stores the final results of processing before the results are released to an
output device.

The secondary memory devices store processed or unprocessed data or information
for future use. Hard disk, Pen drive, CDs, DVDs, etc. are the examples of the
secondary storage memory.

Hard disk Pen drive DVDs

Cache Memory

The cache (pronounced as “cash”) memory is placed in between CPU and main
memory. It consists of static RAMs. It is an extremely fast, small memory whose
access time is closer to the processing speed of CPU. It acts as a high-speed buffer
between CPU and main memory. It is used to temporarily store very active data
and instructions during processing. It is about 100 times faster than that from high-
speed secondary storage like a disk. The modern 32-bit and 64-bit microprocessors
operate at very high speed. Their clock rates are in the range of 333MHz to
1.06GHz where the performance of the CPU depends upon the cache size. It is a
very expensive memory. For example, the Intel Pentium 3.2GHz having 4MB
cache is more expensive than the Intel Celeron with same CPU speed having
2MB cache.

Output Unit

An output unit performs the reverse operations of that of an input unit. It
supplies information obtained from data processing to outside world. Hence, it
links a computer with its external environment. As computers work with binary
code, results produced are also in binary form. Therefore, before supplying the
results to outside world, the system must convert them to acceptable (readable)

31 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

form to human beings. Units called output interfaces accomplish this task.
Output interfaces match the unique physical or electrical characteristics of output
devices (monitors, printer, speaker, etc.) to the requirements of an external
environment. An output unit performs the following functions:
i. It accepts the results produced by a computer, which are in coded form; and

hence, we cannot easily understand them.
ii. It converts these coded results to acceptable (readable) form to us.
iii. It supplies the converted results to the outside world.

Printer Speakers Monitor
Output unit

Bus

Bus is a group of wires used for flow of data and instruction. These wires
are bidirectional, in data bus where data flow in both directions between the
microprocessor, memory, and peripheral devices. The microprocessor uses the data
bus to transfer data from one location to other.

PROCESSOR Address Bus MEMORY
Data Bus

Control Bus

I/O

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 32

Vedanta Let’s Log in Computer Science | Book 9

POINTS TO REMEMBER

A combination of related units that have common purpose of achieving some
objectives is called a system.
An input unit consists of input devices like keyboard, mouse, joystick, etc.
A processing unit consists of processing devices like CPU (Central Processing Unit).
The speed of CPU is measured in hertz. Hertz is also called CPU clock rate or CPU
clock speed.
Control Unit is a part of CPU that controls and co-ordinates the activities of other
units of computer system.
Arithmetic logic unit is a part of CPU that can perform arithmetic operation as well as
logical operation.
Memory unit is also a part of CPU that stores currently executing task.
An output unit consists of output devices like monitor, printer, speaker, etc.
A storage unit consists of primary and secondary storages.
Bus is a group of wires used for flow of data and instruction.

Exercise

1. Fill in the blanks.
a. A system is a group of ............. parts that have a ............. of achieving some objective(s).
b. John Von Neumann ………………..,has not changed.
c. All computer systems perform ……….basic operations.
d. The commonly used input device is a…….…….
e. ………….is used for voice input
f. The ……….is the brain of the computer.

33 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

g. Modern CPUs are called…………..
h. The CPU is composed of thousands of…………..
i. The speed of the CUP is measured in ………..and ………….
j. Intel has released quad-core ……bit chips.
k. The standard Base Memory is …………..
l. A group of ……….is called a byte.
m. The software that boots the system, also called……………
n. There are ……..type of ROM.
o. The cache memory is placed in between……..and ……………
p. Cache memory is very ………memory.
q. …………..performs the reverse operations of that of an input unit.
r. ………….is a group of wires used for flow the data and instruction.
s. The ………uses the data bus to transfer data from…………..to other.

2. Give full forms of the following abbreviations:

a. CPU b. ALU c. GHz d. AMD e. GB f. DRAM

g. SRAM h. PROM i. EPROM j. EEPROM k. I/O

3. Choose the best answer:

i. Memory that loses its data when power is turned off is considered………….memory.

a. volatile b. static c. dynamic d. refreshed

ii. A computer’s CPU consists of millions of tiny switches called…………..

a. bits b. transistors c. registers d. address

iii. The basic components of a modern digital computer are:

a. Input device b. Output device c. Central processor d. All of this

iv. Which of the following is a part of the Central Processing Unit?

a. Printer b. Keyboard c. Mouse d. Arithmetic Logic Unit

v. The two kinds of main memory are:

a. ROM and RAM b. Primary and secondary

c. Floppy disk and hard disk d. Direct and sequential

vi. Which memory is placed in between CPU and main memory?

a. Cache b. ROM c. BUS d. RAM

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 34

Vedanta Let’s Log in Computer Science | Book 9

4. Match the following:

Group A Group B

a. The brain of the computer i. Output Unit

b. Random access memory ii. Bus

c. Read-Only Memory iii. Cache

d. Small high-speed memory. iv. CPU

e. Group of wires v. ROM

f. Converted results to outside world vi. 32 -bit and 64-bit

g. Microprocessors vii. Cyrix, AMD, Intel

h. Chips require very little current viii. DRAM

i. Memory in a modern computer ix. Input Unit

j. Add, subtract, multiply, and divide x. SRAM

k. Renounced processor manufactures xi. RAM

l. Mouse, touch screen xii. ALU

5. Answer the following questions:

a) Define computer system.
b) Mention basic components of computer system.
c) Draw the block diagram of computer system.
d) What are the different parts of CPU?
e) Define CPU with two major sections in it.
f) Differentiate between CU and MU.
g) Why is RAM called non-volatile memory?
h) What is micro-program?
i) What is cache memory? How is it different from a primary memory?
j) Explain how cache memory helps in improving the overall processing speed of a

computer system.
k) Differentiate between input unit and output unit.
l) What is bus in computer system?

Activities

1. Make a Power Point presentation and describe computer system and its main units.
2. Prepare a presentation about "CPU is also known as brain of computer system" and

present in your class as a group work.

35 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

Unit

1.4

For a computer to produce useful output its hardware and software must work
together. Nothing useful can be done with the hardware on its own, and software
cannot be utilized without supporting hardware.
The mechanical devices like disks, disk drives, display screen, keyboards,
printers, motherboards, CPU, chips, register, scanner, etc. that make up
computer are called hardware. Hardware is a tangible part of computer. Hardware
consists of interconnected electronic devices that we can use to control operation,
input, and output in computer.

Microprocessor

A microprocessor is built on to a single piece of silicon, called a wafer or chip that
is commonly no longer than 0.5 cm (0.2 in) along one side and no more than 0.05
cm (0.02 in) thick. Microprocessors are classified in terms of the number of “bits”
of information that can be transferred in parallel and held in their registers. This
number has been steadily increasing with the growth of circuit technology. Thus,
8-bit, 16-bit, and 32-bit microprocessors are now common, and 64-bit chips have
also been developed. The microprocessor is the heart of any normal computer,
whether it is a desktop machine, a server or a laptop. The first microprocessor
was the Intel 4004, introduced in 1971.

microprocessors

It is designed to perform arithmetic and logic operations that make use of small
number-holding areas called registers. Typical microprocessor operations include

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 36

Vedanta Let’s Log in Computer Science | Book 9
adding, subtracting, comparing two numbers, and fetching numbers from one area
to another.

Working of Microprocessor

a. Fetch

The user can give data and instruction which is stored in RAM. Microprocessor
receives data and instruction according to necessity and requirement which is
known as fetch. So, fetch means getting instruction from memory.

b. Decode

The main function of the microprocessor is to change fetch instruction into
decode instruction. The given instruction is separated for calculation of arithmetic
or logical data. So, decode means deciding what the instruction means.

c. Execute

Microprocessor can perform the main task in this unit. For example, ALU is
used for mathematical calculation. So, "execute" means performing the instruction.

d. Write back

Microprocessor processes the instructions and produces the result which is to
transfer data to memory for storage. This is called "write back".

The complete cycle of four units as fetch, decode, execute and write back of
microprocessor for processing the instruction is called the instruction cycle.

Motherboard Motherboard

The motherboard or printed circuit board (PCB) is a
rigid rectangular card containing the circuitry that
connects the processor to the other hardware. The
motherboard is an example of a circuit board. The
motherboard contains the connectors for attaching
many internal additional devices such as CPU,
BIOS, memory, mass storage interfaces, serial and
parallel ports, expansion slots, and all the controllers
that are required to control standard peripheral
devices, such as the display screen, keyboard, and

37 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

hard drive. Collectively, all these chips that reside on the motherboard are known
as the motherboard’s chipset. You can think of the motherboard as the master
circuit board in a computer.
These chipsets are connected to the motherboard directly or using cables. Electric
path or connections that are specially used for the communication between the
various components of the motherboard are termed as BUS. The motherboard
bus can be one of two types: internal and external. An internal bus serves as
the communication path of the motherboard. It links the different parts of the
computer to the CPU and the main memory. Its primary task is to send data and
instructions to the different parts within the motherboard, including the external
bus. The external type of motherboard bus, which is also known as the expansion
bus, serves as the interface for peripheral devices like hard disks, CD-ROM drives,
and flash drives to get connected to the CPU. The shape of each interface is unique.
This prevents plugging a device to a wrong port, which could cause damage to the
device while being connected to the CPU. All buses have a control bus, data bus,
address bus, and power bus.

Control bus

The control bus is used by the CPU to send signals to the different parts of
the computer system to keep the actions of the different parts coordinated.

Data bus

The data bus provides the path to transfer data and instructions among the
different components of computer.

Address bus

Data bus is assisted by the address bus, which provides the physical address
of data in the system memory to facilitate data transfers.

Power bus

The power bus energizes the different components of the computer system.

Memory

Memory is the workspace for the computer’s processor. It is built within computer
that stores the unprocessed and processed data as well as the program instructions.
Personal computers use several different types of memory, but the most important
are of two types:

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 38

Vedanta Let’s Log in Computer Science | Book 9

a. Primary Memory

We often call RAM (Random Access Memory) is volatile. It is limited in
capacity and temporary in nature because the data and programs remain there
only as long as the computer has electrical power or is not reset. Today’s personal
computer generally have at least 2 GB RAM or more.
Read-Only Memory or ROM is a non-volatile memory chip in which data is stored
permanently. It cannot be altered by usual programs. There are three types of ROM
that is PROM (Programmable Read-Only Memory), EPROM (Erasable PROM),
and EEPROM (Electrically Erasable PROM).

Different types of ROM

b. Secondary Memory

Device that is supplement to main memory is called secondary (Auxiliary
/ Backing) memory. The common secondary memory used in computers systems
are Tape, Zip Disk, Super Disk, Hard Disk, Optical Disk, Pen Drive, etc. They are
used for storing system programs, large data files, and other backup information.

Tape Tape

Magnetic tape is a serial access type storage
device. It is suitable for backup storage in servers
and workstations. Its main drawback is that it
stores information sequentially. A file or particular
information stored on a magnetic tape cannot be
accessed directly on random basis as it is done in
the case of hard disk or floppy disk.

A magnetic tape is made of Mylar plastic material
coated with magnetic material (iron oxide) on only
one side of the tape. Magnetic tapes are available

39 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9
in ½ inch, ¼ inch. 8mm and 3mm sizes. It is typical length is 2400 feet and have
capacities as high as 200 GB and more.

Zip Disk Zip Disk

It consists of a single hard disk platter
encased in a plastic cartridge. The disk is
commonly of 3.5 inch size having storage
capacity of about 100 MB to 750 MB made by
Iomega Corp. The storage capacity slightly
varies depending on the formatting style
used by a computer system with which it is
used. Its disk drive, called zip drive, maybe
of portable or fixed type. A zip disk can be
easily loaded/unloaded into a zip drive.

Hard Disk

A hard disk includes one or more platters mounted on a central spindle like a stack
of rigid diskettes. Each platter is covered with a magnetic coating, and the entire
unit is encased in a sealed chamber. Unlike diskettes, where the disk and drive
are separate, the hard disk and drive are a single unit. It includes the hard disk,
the motor that spins the platters, and a set of read/write heads. The hard disks
available today can store several hundred terabytes the largest store 10 TB or
even more.

Hard disks

The hard disks found in most PCs spin at a speed of 3600, 5400, 7200 or 10,000
revolutions per minute (rpm). Very-high-performance disk found in workstation
and server can spin as fast as 15,000 rpm. The speed at which the disk spins is
a major factor of its overall performance. The hard disk’s high rotational speed
allows more data to be recorded on the disk’s surface. This is because a faster-

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 40

Vedanta Let’s Log in Computer Science | Book 9

spinning disk can use smaller magnetic charges to make current flow through the
read/write head. The drive’s heads also can use a lower-intensity current to record
data on the disk.

Like diskettes, hard disks generally store 512 bytes of data in a sector, but hard
disks can have more sectors per track – 54, 63, or even more sectors per track are
not uncommon. Basic hard drive components are as follows:

a. Disk Platters
b. Read/Write Head
c. Head actuator mechanism
d. Spindle motor
e. Logic board
f. Cable and Connectors
g. Configuration items (such as jumpers or switches)

Read/Write Head
Platters

Spindle Actuator arm
Landing Zone Actuator Axis

Actuator

Internal part of hard disk

Optical Storage Disc

The most popular alternatives to magnetic storage systems are optical systems,
including CD-ROM, DVD-ROM, and their variants. These devices fall into the
category of optical storage because they store data on a reflective surface; so, it can
be read by a beam of laser light. A laser uses a concentrated, narrow beam of light,
focused and directed with lenses, prisms, and mirrors. The familiar audio compact
disc is a popular medium for storing music. In the computer world, however, the
medium is called compact disc-read-only memory (CD-ROM). CD-ROM uses the

41 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9
same technology used to produce music CDs. If your computer has a CD-ROM
drive, a sound card, and speakers, you can play audio CDs on your PC.
A CD-ROM drive reads digital data from a spinning disc by focusing a laser on the
disc’s surface. Some areas of disc reflect the laser light into a sensor, and other areas
scatter the light. A spot that reflects the laser beams into the sensor is interpreted as
a 1, and the absence of a reflection is interpreted as a 0.
Data is laid out on a CD-ROM disc (12cm diameter) in a long, continuous spiral.
Data is stored in the form of lands, which are flat areas on the metal surface,
and pits, which are depressions or hollows. A land reflects the laser light into the
sensor (indicating a data bit of 1) and pit scatters the light (indicating a data bit
of 0). A standard compact disc can store 650 MB of data or about 70 minutes of
audio. A newer generation of compact discs, however, can hold 700 MB of data or
80 minutes of audio. Compared to hard disk drives, CD-ROM drives are slow. One
reason has to do with the changing rotational speed of the disk.

The first CD-ROM drives could read data at 150Kbps (kilobytes per second) and be
known as single-speed drives. Today, the speed of CD-ROM drive is expressed as
multiple of the original drive’s speed – 2x, 4x, 8x, and so on. A 2x drive reads data
at a rate of 300KBps. The latest, fastest available CD-ROM drive is 75x: it could
read data at a rate of 11,250 KBps. The different types of CD-ROM are WORM
(Write Once Read Many) and CD/RW (CD-ReWritable). You can write data onto
special rewritable compact discs (called CD-RW discs) and overwrite it with new
data. In other words, we can change the contents of a CD-RW disc.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 42

Vedanta Let’s Log in Computer Science | Book 9

DVD - ROM

Many of today’s new PCs feature a built-in digital video disc-Read-Only
Memory (DVD-ROM) drive rather than a standard CD-ROM drive. DVD-ROM
is a high density medium capable of storing a full-length movie on a single disc.
DVD-ROM achieves such high storage capacities
by using both sides of the disc and special data-
compression technologies and by using extremely
small tracks for storing data. The latest generation
of DVD-ROM disc uses layers of data tracks,
effectively doubling their capacity. The device’s
laser beam can read data from the first layer and
then look through it to read data from the second
layer. DVDs look like CDs. DVD-ROM drives can
play ordinary CD-ROM discs. A slightly different
player, the DVD movie player, connects to your DVD

television and plays movies like a VCR. The DVD movie player also plays audio
CDs as well as many types of data CDs, such as home-recorded audio discs, video
CDs, and others. Since each side of a standard DVD-ROM disc can hold 4.7 GB,
these discs can contain as much as 9.4 GB of data. Dual layer DVD-ROM discs can
hold 17 GB of data. The different types of DVD drive are COMBO DRIVE (CD-
RW / DVD-read) and DVD-RW (DVD- ReWritable). The next technology of DVD is
Blue Ray Disc which can hold 25-50 GB of Data.

Advantages of optical discs
1. Cost-per-bit of storage for optical discs is very low
2. Optical discs have data storage life in excess of 30

years.
3. Due to their compact size and lightweight, optical

discs are easy to handle, store, and port from one
place to another.
4. A computer having a DVD drive can be used to play
DVDs allowing it to be used for watching videos
such as movies.

SSD (Solid State Drive)

Hard disk can be replaced and upgraded by SSD (Solid State Drive) as a new
technology. Semiconductor chips are used to store data in SSD. The speed to read
and write data is greater than hard disk. So, its price is more expensive than hard

43 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9
disk. Laptop, notebook, ultrabook, etc. are used SSD. Its storage capacity is about
4 TB but various companies try to develop SSD with more storage capacity.

Solid State Drives (SSD)

Differences between SSD and Hard Disk

S.No. Hard disk SSD

1 It is heavier than SSD. It is lighter than hard disk.

2 The storage capacity is 500 GB to 100 TB. The storage capacity is 1 TB to 4 TB.

3 It is cheaper than SSD. It is more expensive than hard disk.

4 It takes 6-7 watt electricity. It takes 2-3 watt electricity.

5 The file writing speed is 50-120 MB/S The file writing speed is 200-550 MB/S

(mega byte per second) (mega byte per second)

6 It is made up of aluminium material. It is made up of semiconductor micro
chip.

External Hard Drive

The working principle of hard disk is similar to external External Hard Drive
hard drive but it cannot be put inside CPU casing. It
can externally connect with USB (Universal Serial
Bus) port. It is portable and easy to carry. It is used
to transfer data, information, and software from one
computer to another.

Flash Drive (Pen Drive)

Flash drive is a compact device of the size of a pen: it comes in various shapes and
stylish designs (such as pen shape). It may have different added features (such as
with a camera, with a built-in MP3/WMA/FM radio Play back and recording). It
enables easy transport of data from one computer to another.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 44

Vedanta Let’s Log in Computer Science | Book 9

In fact, many users carry a flash memory drive on their Pendrive
key chain. It is a plug-and-play device that simply
plugs into a USB (Universal Serial Bus) or FireWire
port of a computer. The flash memory is non-volatile
and Electrically Erasable Programmable Read-Only
Memory (EEPROM) chip. The data retention capability
of this device is more than 10 years. Recent in the market
available storage capacities are 4GB, 8GB, 32GB, 64GB,
512GB up to 2TB.

Units of Memory Measurement

The smallest unit of memory measurement is a bit (binary digit- 0 or 1). The data
stored in a computer is binary digit, byte, kilobyte, megabyte, gigabyte, terabyte,
etc.

a. Bit

Bit stands for Binary digit. The value of the binary digit is 0 or 1.

b. Nibble

Nibble is the combination of 4 bits.

c. Byte

Byte is the combination of 8 bits.

The units of memory measurements are as follows:

S.No. Memory Unit Description
1 Bit 1 Bit = 0 or 1
2 Nibble 1 Nibble = 4 Bits
3 Byte 1 Byte = 8 Bits
4 Kilobyte (KB) 1 Kilobyte (KB) = 1024 Bytes
5 Megabyte (MB) 1 Megabyte (MB) = 1024 KB
6 Gigabyte (GB) 1 Gigabyte (GB) = 1024 MB
7 Terabyte (TB) 1 Terabyte (TB)= 1024 GB
8 Petabyte (PB) 1 Petabyte (PB) = 1024 TB
9 Exabyte (EB) 1 Exabyte (EB) = 1024 PB
10 Zettabyte(ZB) 1 Zettabyte(ZB)= 1024 EB
11 Yottabyte(YB) 1 Yottabyte(YB)=1024ZB

45 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

Input Devices

Input device accepts data and instructions from the user or another computer
system. An input device converts input data and instructions into suitable binary
form (such as ASCII) which can be accepted by the computer. The most common
input device is the keyboard, which accepts letters, numbers, and commands from
the user. Another important type of input device is the mouse which lets you select
options from on-screen menus. A variety of other input devices work with personal
computers, too.

Keyboard

The keyboard was one of the first peripherals to be used with computers, and it is
still the primary input device for entering text and numbers. A standard keyboard
includes about 100 keys: each key sends a different signal to the CPU.
Keyboards come in many styles. The various models differ in size, shape, and
feel. Except for a few special-purpose keys, most keyboards are laid out almost
identically. Among IBM-compatible computers, the most common keyboard layout
is the IBM Enhanced Keyboard. It has about 100 keys arranged in five groups as
Alphanumeric Keys, Modifier Keys, Numeric Keypad, Function Keys, and
Cursor-Movements Keys.

keyboard

The alphanumeric keys is the area of the keyboard that looks like a typewriter’s
keys which are arranged in the same way on almost every keyboard. Sometimes
this common arrangement is called the QWERT (pronounced KWER-tee) layout
because of the first six keys on the top row of letters Q, W, E ,R, T, and Y.

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 46

Vedanta Let’s Log in Computer Science | Book 9

The SHIFT, ALT (Alternate), and CTRL (Control) keys are called modifier keys
because they modify the input of other keys. The numeric keypad is usually
located on the right side of the keyboard. The function keys, which are labeled
F1, F2, F3, and so on are usually arranged in a row along the top of the keyboard.
Where cursor-movement keys, which let us move around the screen without
using a mouse (arrow key, Insert, Home, Page Up, Delete, End, Pg Down, PrtSc
SysRq, etc).
Since 1996, nearly all IBM-compatible keyboards have included two additional
special-purpose keys to work with the Windows operating systems: Start (windows
logo key) and Shortcut key. One of the latest trends in keyboard technology is the
addition of Internet and multimedia controls.

Mouse

A mouse is an input device that we can move around on a
flat surface (usually on a desk or keyboard tray) and control
the pointer. The pointer (also called the mouse pointer) is
an on-screen object, usually an arrow, that is used to select
text, access menus, and interact with programs files or data
that appear on the screen. The mechanical mouse is the most
common type of pointing device. A mechanical mouse contains Mouse

a small rubber ball that protrudes through a hole in the bottom of the mouse’ case.
Another popular type of mouse, the optical mouse is non-mechanical. This type
of mouse emits a beam of light from its underside: it uses the light’s reflection to
judge the distance, direction, and speed of its travel.

Joystick Joystick

Like mouse, joystick is also a pointing-device. It is used to “fly” or
“drive” through a game, directing a vehicle or character. A joystick
is a stick which has spherical ball at its lower end as well as at its
upper end. The lower spherical ball moves in a socket. The joystick
can be moved to right or left, or forward or backward.

Touch Pad

A touch pad feels less mechanical than a mouse or
trackball because the user simply moves a finger on
the pad. A touch pad has two parts: one part acts as
a button, while the other part emulates a mouse pad

Touch Pad

47 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9

on which the user traces the location of the cursor with a finger. Many portable
computers have built-in trackball or touch pad as input devices.

Track Ball

Trackball is also a pointing device and contains a ball which
can rotate in any direction. The user spins the ball in different
directions to move the cursor on the monitor. It is used on a
laptop computer where there is no space for conventional mouse.

Digital Camera Track Ball

Digital cameras work much like PC video cameras, except that digital cameras
are portable, handheld devices that capture still images. Whereas normal film
cameras capture images on a specially coated film, digital cameras capture images
electronically. The digital camera digitizes the image, compresses it and stores it
on a special memory card. The user can then copy the information to a PC, where
the image can be edited, copied, printed, embedded in a document, or transmitted
to another user.

Most digital cameras can store dozens Digital Camera
of high-resolution images at a time,
and most cameras accept additional
memory that increases their capacity
even further. Digital cameras enable
users to shoot a subject and quickly
load the images onto their computers.
This process saves the step of acquiring
existing photographs or developing and
printing film-based photos which must
be scanned into the computer.

Microphone

Today, many new PCs are equipped with complete
multimedia capabilities. Nowadays, sound capabilities
are standard in computers: microphones are becoming
increasingly important as input devices to record speech.
Spoken input is used often in multimedia, especially
when the presentation can benefit from narration. Most
PCs now have phone-dialing capabilities. If you have a

Microphone

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 48

Vedanta Let’s Log in Computer Science | Book 9

microphone and speakers (or a headset microphone with earphones), you can use
your PC to make telephone calls. Microphones also make the PC useful for audio
and videoconferencing over the Internet.

Graphic Digitizer

Digitizer tablets or graphics tablets are pressure-
sensitive data input devices that allow users to select
and draw images with a special pen called a stylus
or a mouse-like device called a puck. Pucks feature
a series of buttons and a lens with crosshairs that
allows users to select images with greater accuracy.
Both pens and pucks can be wireless devices or
attached to digitizer tablets via cords or wires. The
drawings that users produce with digitizer tables
are stored as mathematical line segments. Outputs Graphic Digitizer

can be sent to computer aided design (CAD) applications, graphics programs, or
related software applications.

Bar Code Reader

A barcode reader is a hand-held or stationary
input device used to capture and read information
contained in a bar code. A barcode reader merely
captures and translates the barcode into numbers
and/or letters. The data must be sent to a computer
so that a software application can make sense of
the data. Barcode scanners can be connected to a
computer through a serial port, keyboard port, or
an interface device called a wedge. It works by
directing a beam of light across the bar code and
measuring the amount of light that is reflected
back. The dark bars on a barcode reflect less light Bar Code Reader

than the white spaces between them. The scanner converts the light energy into
electrical energy, which is then converted into data by the decoder and forwarded
to a computer.

Scanner

An image scanner is like a photocopy machine, but
instead of copying an image onto paper, it transfers
the image directly to the computer. A scanned image

Scanner

49 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur

Vedanta Let’s Log in Computer Science | Book 9
is usually a bitmap file, but software tools are available for translating images into
a vector format.

Optical Character Readers (OCR)

It is technology that enables a computer to translate
optically scanned data into character codes. An OCR
reader scans the document using the photo electric
devise to convert the shape into electric signals. OCR
is widely used in Airline, Banks, Postal Offices, etc.

Optical Mark Reader (OMR) Optical Character Readers (OCR)
Optical Mark Reader (OMR)
These devices are capable of recognizing
a pre-specified type of mark made by
pencil or pen. For example in MBBS
Entrance Exam, in objective type tests
applicants mark their choices of correct
answers on a special pre-printed test
scoring sheet by darkening a small
square, circular, or oval shaped box with
a pencil. These answer sheets are fed
directly to a computer for grading with
the use of an optical mark reader.

Output Device

An output device is an electromechanical device that accepts data from a computer
and translates them into a form suitable for use by outside world (users). Several
output devices are available today. They can be broadly classified into the following
categories:

a. Soft-copy Output

A soft-copy output is not produced on a paper or some material that
can be touched and carried for being shown to others. They are temporary
in nature. For example, monitor, or words spoken out by a voice response
system are some of its type.

b. Hard-copy Output

A hard copy output is produced on a paper or some material that can
be touched and carried for being shown to others as authentic or proof. They
are permanent in nature and can be kept in paper files or can be looked later

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 50