JBD Computer Studies Book 9

Approved by the Government of Nepal, Ministry of Education, Curriculum Development
Centre (CDC), Sanothimi, Bhaktapur, Nepal as an additional material for schools.

JCBD omputer

Studies

9

Authors
Sushma Pradhan
Kiran Kumar Shrestha

JBD Publication Pvt. Ltd.
Bhotahity, Kathmandu, Nepal

Published By

JBD Publication Pvt. Ltd.

Bhotahity, Kathmandu, Nepal
Tel: 01 - 4252371, 4313294
Email: [email protected]
Web : www.jbdbooks.com

© Reserved with publishers

First Edition : 2010 (2068 BS)
Second Edition (Revised and Updated) : 2015 (2072 BS)

Edition : Revised, 2019 (2076 BS)

ISBN: 978-9937-544-80-1

Authors:
Mrs. Sushma Pradhan
Mr. Kiran Kumar Shrestha

Mahabir Offset Press, Tel: 025-521634

Preface

Progress in information technology is affecting our lives more than
ever. Computers have played a key role in this, and they too have
evolved at a fast pace. Today, they are used in almost every sphere of
life. It has become imperative for us to know the usage of computers.
Computer education makes a child understand computer and its basic
functions.

The ‘Computer Studies’ series is a set of computer books meant for
the students of Primary and Middle School levels. The books have
followed the guidelines prepared by CDC, Government of Nepal. The
book 9 of this series is recommended for use in Class 9.

The series ‘Computer Studies’ has been written to impart computer
skills to students at different school stages. It is well-focused on building
a strong foundation and achieving age-appropriate competency. Each
chapter in the book has a separate overview with plenty of illustrations
and text supported by screenshots on a Windows 7 platform. It is
written in a very simple language and chapters are presented in a user-
friendly format.

Suggestions for further improvement from the users of the series will
be whole-heartedly appreciated and gratefully acknowledged.

Authors

Contents 5
15
1. Introduction to Computers 29
2. Evolution of Computers 37
3. Computers for Everyone 49
4. Anatomy of a Computer System 61
5. Input and Output Devices 72
6. Secondary Storage Technology 79
7. Computer Software Concepts 93
8. Computer Number System 107
9. IT Policy of Nepal and E-Government 131
10. Introduction to Operating System 153
11. Introduction to HTML 163
12. Programs and Programming Languages 175
13. Programming Techniques 190
14. Basics of QBASIC Programming 203
15. QBASIC Statements 222
16. QBASIC Control Statements 241
17. Library Functions in QBASIC 253
18. Arrays in QBASIC
Model Test Paper

Chapter 1

INTRODUCTION
TO

COMPUTERS

Objectives

After completing this chapter, you will be able to:
y Define a computer and explain the major characteristics of a computer.
y Describe the major applications of a computer.
y State the positive impacts of a computer.
y State the negative impacts of a computer.

C Ooncept verview

Computers have now become an integral part of our daily lives. They have
invaded all types of workplaces, from offices to factories and has performed
a wide variety of activities reliably, accurately and quickly. Were the power to
computers ever shut off, business and industry would almost instantly come to
a halt. Without computers, the modern corporation could not even exist. They
have become so deeply embedded in information processing and communication
systems that almost no activity would be possible without them. They are a fact
of life, a common thread that ties together our education, work and home life. It
has made the world function much faster and accurate.
The word computer comes from the word “compute” which means to calculate. It
is a device capable of accepting data in the form of facts and figures, manipulating
them in a prescribed way, and supplying the results of these processes as
meaningful information. This device usually consists of input devices Central
Processing Unit, storage devices and output devices. Computers works on the
principle of Input-Process-Output cycle.

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In this cycle, the computer performs the following functions:
• Receives input in the form of data and instructions.
• Processes the data on the basis of the instructions.
• Displays the processed data as output.
This can be schematically illustrated below:

Characteristics of a Computer
All computers have certain common characteristics irrespective of their types and
sizes. Computers are capable of doing complex activities and operations. The
increasing popularity of computers has proved that they are very powerful and
useful tools. The characteristics possessed by computers can be listed as follows:

Speed
Computer can do routine calculations at tremendous speed in fact with the
speed of light. This speed allows one to do computations that would otherwise
be impossible. Progress would be considerably slowed down without them. The
speed of a computer at performing a single operation can be measured in terms of:
• Milliseconds- One thousandth of a second (1/1000).
• Microseconds-One millionth of a second (1/1000000).
• Nanoseconds-One billionth of a second (1/1000000000).
• Picoseconds-One trillionth of a second (1/1000000000000).

Word Length
All digital computers operate on binary digits-0 and 1 to represent any kind of
data. Bit stands for binary digit. It is the smallest unit of information a computer
can hold. The value of a bit is 1 or 0. Byte is the amount of memory space used to
store one character, which is usually 8 bits. The number of bits that a computer can
process at a time in parallel is called word length. Commonly used word lengths
are 8, 16, 32 or 64 bits. Word length is the measure of the computing power of a
computer. The longer the word length, the more powerful the computer is.

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Accuracy
Computers operate with almost 100% accuracy. They can perform calculations
with such great accuracy as their circuits have no mechanical parts that wear
and tear. They only execute instructions input by the user. There may be errors
produced by the computers. Sometimes, it is due to the fault in the machine and
more often due to ‘bugs’ in the programs. If the input data are not correct, this
may also lead to incorrect output. The computers follow the simple rule of GIGO
(Garbage In Garbage Out).

Automation
Computers are quite capable of functioning automatically, once the process is
given to the computer. They do not require any instruction from the operator
at any stage of the process. Computers can be programmed to perform a series
of complex tasks involving multiple programs. Computers will execute the pro-
grams in the correct sequence, provided they are programmed correctly.

Diligence
Human beings suffer from physical and mental fatigue. They cannot perform the
same task over and over again with the same speed, accuracy and enthusiasm as
in the first time. This will affect the performance. Being a machine, a computer
does not suffer from such weaknesses. The computer is capable of performing
task repeatedly at the same level of speed and accuracy even if it has to carry
complex operation for a long period of time.

Versatility
Computers are versatile (can do many types of jobs). It can carry out processes
ranging from simple mathematical calculations to highly complex and logical
evaluations for any extended period of time. Computers can communicate with
other computers and can receive and send data in various forms such as text,
video, etc. This ability of computer to communicate to one another has led to the
development of computer networks, Internet, and so on. All this is possible be-
cause of computers and other related technologies.

Common Data Used
One item can be involved in several different procedures or accessed, update and
inspected by a number of different users. This can hinder the work of those who
need access to data. As the time is changing, more and more facilities are being
added to the computers they can perform but in practical life many tasks are lim-
ited to these basic operations.

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Computer Studies-9 7

Limitations of a Computer

The computer can out perform human beings in speed, memory and accuracy
but still the computer has limitations. Computer is one of the most powerful tools
ever developed. It has many useful applications but however, there are some
negative points of computer.

• A computer is a dumb machine. A computer cannot do anything unless they
are first programmed with specific instructions. Computers cannot decide
how they are to be programmed or provide their own input. They cannot
interpret the data they generate and implement any decisions that they
suggest.

• Computer needs a proper environment for its working (i.e fixed temperature
and a dust free environment).

• Computer is a machine which may break down any time. Interruption in
electrical current may cause system components to malfunction resulting in
the loss of valuable data.

• Computer cannot take care of itself like a human.

Applications of a Computer

Computers have woven into the very fabric of modern life. It has become an
indispensible entity in every walk of life. The practical applications of computers
are endless. Let us have a brief idea of some of the impacts of computer usage in
various sectors of our society. A broad classification of its uses in varied fields are:

Computers in Education

Computers are helping educators make
significant changes to the learning process.
Computers help children to be in control of
their experience, to set their own pace, and to
select the level of challenge with which they
feel comfortable. Computers help children to
use all of their senses to extract information.
Computers fascinate kids and can draw their
full attention, which often results in a deeper
focus and concentration. Many schools
now have computers that are connected to
internal networks and the Internet, allowing
students to easily communicate with one
another, teachers, and administrators. They
provide information directly into the hands
of students.

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New computer-based education and training programs allow instruction to be
more tailored to individual students. Computer has changed education system
by widening education opportunities. Distance education allows students who
cannot attend school in person to take courses on-line. They are also used in
administration for time table generation, examination processing, payroll
generation for staff and admission selection process.

Computers in Scientific Research

Computers play a crucial role in conducting the basic underlying science such
as observing and collecting data, classifying and analyzing, modelling and
simulating, and speculating and theorizing. They are also used in the design
and operation of man made satellites, space exploration vehicles, rockets, and
in training of astronauts. Computer models and simulations allow scientists
to build complex models of just about any object, organism, or process and to
examine how the model operates under certain conditions.

Computers at Home

Computers are used at homes for learning, playing games and fun. Many of
the educational software programs are used by children and adults in homes.
Edutainment programs enrich students’ knowledge and skills. Encyclopedia,
dictionaries, telephone directories and medical references are now available in
CD-ROM which contains multimedia capabilities. The Internet connections also
provide electronic mail, discussion groups, and other communication options for
home users. Apart from learning, they are also used for playing computer games
and video games.

Computers in Medicine

Computers are revolutionizing the medical field.
Computers are used in the medical field for
performing a wide variety of tasks. They are used
in medicine to diagnose and monitor patients’s
illnesses. Computer controlled ultra-sound
scanners help doctors to screen patients very
accurately. They are used in the administration
of hospitals and doctors’ surgeries, and storing
patients’ records. Some hospitals are now
experimenting with storing medical records
on smart cards kept by the patient and taken with them every time they visit a
doctor. The smart card can store a complete medical history and can be up-dated
at the end of each visits.

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Computers in Financial Management
Every organization has limited financial
resources that must be utilized in
a planned way. Computers help
organizations to prepare budgets and
allocate limited financial resources
among competing requirements. They
also help track and monitor the expenses
of an organization thereby leading to an
effective management of funds. They also
facilitate computation of the monthly
wage bills of an organization.

Positive Impacts of Computers
Computers are one of the most powerful forces in the society today. They are
being put to use everywhere. They continue to grow and open new horizons of
discovery and application such as the electronic office and the home computer
centre. They have strengthened man’s powers in numerical computations and
information processing and thereby increased the effectiveness of organizations.
Some of the positive impacts that computer usages may have on people are stated
below:
• Computers may help improve the quality of the products and services we

receive.
• Computer can control devices that allow severely handicapped persons to

feed themselves even though they have no upper limb responses.
• Computer-controlled antilock braking systems in aircrafts and cars help

prevent dangerous skids and produce optimum stopping distances in all
weather conditions.

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• Computers permit gas utility companies to do a better job of managing and
controlling the pipeline leaks that can seriously jeopardize public safety.

• Computers use can lead to improved student performance in thinking
logically, formulating problem – solving procedures, and understanding
relationships.

• Computers can help you budget and balance your checkbook, control your
installment purchases, control your home’s energy use and analyze your
investments.

• Computers also progress the technical skills in a person in doing research as
well as in the use of the computer itself.

Negative Impacts of Computers
Though there are several benefits, there are some dangers also because of
computerization. Some of these dangers to the society are listed below:
• Pollution caused by the production of computer hardware, as well as from the

cleaning agents used to clean computers, is a great hazard to the environment
and the people that live in it. People leave their computers on non-stop
resulting in a lot of energy consumption and enormous amounts of paper
are being used daily to print out electronically stored data. It causes health
problems as well as economic problems and is in urgent need of treatment.
• Computerization may result in reduction of clerical type of jobs since the
amount of work that a person using a computer can do is more than that
done by a number of persons. Computers cause huge unemployment and
deskilling of jobs.
• Computer crime can take the form of the theft of money, the theft of information
and destruction of data by computer viruses.
• The growth of computerized record-keeping brings dangers to privacy.
• Computerized systems and information databases in an organization face
various types of security threats. Data and information get damaged or
destroyed if any of the security threats materialize. This results in a loss to the
organization.

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C Dompu- ictionary

Computer : An electronic device that accepts input, performs
calculations, and produces the required results.

Data : Raw facts that can be shaped and formed to create
information.

Bug : An error in a computer program or in the computer’s
hardware that causes repeated malfunctions.

Debug : To fix problems in hardware or software.

GIGO : The idea that if the data put into a computer or
program is not good, the result that comes back will
not be worth much.

Information : Data that have been shaped by human into a
meaningful and useful form.

Recap

• A computer may be defined as a digital electronic processing device that can
accept data (input), process data arithmetically and logically, produce results
(output) from the processing and store results for future use operating under
the control of instructions stored in its own memory unit.

• An error in a computer program or hardware is called bug and the process of
removing the error is called debugging.

• All the general purpose computers require the following hardware
components: input device, central processing unit, memory unit, storage
device and output device.

• Byte is the amount of memory space used to store one character, which is
usually 8 bits.

• GIGO is an acronym for Garbage In Garbage Out. The term GIGO is normally
used to make the point that if the input data is bad (garbage in) then the
output data will also be bad (garbage out).

• The modern computers possess the following abilities:

i. Performing complex and repetitive calculations rapidly and accurately.

ii. Make decisions on the basis of given conditions.

iii. Correct and modify certain parameters automatically.

iv. Store large amounts of data and information for subsequent manipulations.

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Review Yourself

1. State whether the following statements are true or false.
a. Computers work on the principle of Input-Process-Output cycle.
b. A microsecond is 10000 times longer than a picosecond.
c. Gigabyte is the measure of the computing power of a computer.
d. A computer cannot do anything unless they are first programmed with
specific instructions.
e. Computer has changed education system by widening education opportunities.
f. Computers may help improve the quality of the products and services we receive.
g. The growth of computerized record-keeping brings dangers to privacy.

2. Fill in the blanks.
a. Computers works on the principle of ________________ cycle.

b. ______________isequivalenttoonetrillionthofasecond(1/1000000000000).

c. _____________is the smallest unit of information a computer can hold.

d. The longer the ____________, the more powerful the computer is.

e. ______________ allows students who cannot attend school in person to
take courses on-line.

f. The _____________ connections also provide electronic mail, discussion
groups, and other communication options for home users.

g. ______________ is normally used to make the point that if the input data
is bad (garbage in) then the output data will also be bad (garbage out).

3. Match the following. An electronic device that accepts input, performs
Data calculations, and produces the required results.
Output
GIGO Raw facts that can be shaped and formed to create
Computer information.

Bug An error in a computer program or in the computer’s
hardware that causes repeated malfunctions.

The idea that if the data put into a computer or
program is not good, the result that comes back will
not be worth much.

The derivation of the final result as meaningful
information for the user.

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4. Select the best answer from the list of choices.

a. Computers works on the principle of:

i. Input-Process-Output cycle ii. Process-Input-Output cycle

iii. Output-Process-Input cycle
b. A computer derives its basic strength from:

i. speed ii. accuracy iii. All of the above

c. One millionth of a second is called:

i. Millisecond ii. Microsecond iii. Nanosecond

d. An error in a computer program or in the computer’s hardware that
causes repeated malfunctions.

i. Debug ii. Bug iii. Fault

e. Data that have been shaped by human into a meaningful and useful
form.

i. Input ii. Information iii. Output

5. Answer the following questions.

a. What is a computer? Explain any five characteristics of a computer in
short.

b. Define each of the following terms:

i. Data ii. Program iii. Bug

c. What is meant by garbage-in-garbage-out?

d. What are the main limitations of a computer?

e. How have computers affected education?

f. What roles do computers play in medicine?

g. What effects have computers had on the scientific research?

h. What roles do computers play in financial management?

i. List any three positive impacts of computer technology in our society.

j. What are the two negative impacts of computer technology in our
society?

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Chapter 2

EVOLUTION
OF

COMPUTERS

Objectives

After completing this chapter, you will be able to:
y List the features of an abacus.
y Name the inventor of Napier’s bones and list the features of Napier’s bones.
y Explain the important contributions made by Charles Babbage.
y List the features of difference engine and analytical engine.
y List the features of Harvard Mark - I
y List the features of Universal Automatic Computer-I

C Ooncept verview

The start of modern computer science can be traced back to long ago when man
dwelled in caves or in forests, and lived in groups for protection and survival from
the harsh elements on the Earth. Calculation was a need from the early days when
it was necessary to account to others for individual or group actions, particularly
in relation to maintaining inventories (of flocks of sheep) or reconciling finances.
Early man counted by means of matching one set of objects with another set
(stones and sheep). The operations of addition and subtraction were simply the
operations of adding or subtracting groups of objects to the sack of counting
stones or pebbles. Early counting tables, named abaci, not only formalized this
counting method but also introduced the concept of positional notation that we
use today. These tools had the added advantage of storing easily the intermediate
results for later use but the computing speed was slow. This necessitated the
development of new machines for better and faster computation.

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Abacus
Abacus is one of the first mechanical
calculating devices created by the Chinese.
It consists of a rectangular frame carrying a
number of rods or wires. A horizontal beam or
mid bar separates the frame into two sections,
known as the upper deck and the lower deck.
On the upper deck of each rod are two beads
and on the lower deck five beads. The beads
below the midbar represent one of that rod’s
units (that is, a one, a ten, a hundred, and so
forth), and those above represent five. Beads
are moved from the outer position toward the
crossbeam when used to represent a number.

Napier’s Bone
John Napier, a Scottish mathematician, developed the system of logarithms
in 1614 which greatly assisted in arithmetic calculations. He also invented a
small instrument called Napier’s Bones in 1617. These bones were made up of
rectangular strips of wood or bones with figures marked on one side. Each rod
was divided into ten squares and in the top square was a digit from 0 to 9. This
simple device enabled to carry out multiplication faster, provided one of the
numbers was a single digit number.

Slide Rule
William Oughtred, an English mathematician invented Slide Rule in 1620.
He wrote the “Circles of Proportion and Horizontal Instrument” in 1632. He
invented both the standard rectilinear slide rule and the less commonly used
slide rule. He used the principle of bones and logarithms. It is a device consisting
of two logarithmically scaled rules mounted to slide along each other so that
multiplication, division, and other more complex computations are reduced to
the mechanical equivalent of addition or subtraction. It is considered as the first
analog computing device.

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Pascal’s Calculator
Blaise Pascal, a French philosopher, mathematician, and physicist, invented the
first mechanical calculator called Pascalina in 1642. The calculator had spoked
metal wheel dials, with the digits 0 through 9 displayed around the circumfer-
ence of each wheel. The numbers were entered by dialing a series of numbered
wheels, where the movement of the wheels started at 9 and moved to 0. An au-
tomatic carry over system was accomplished by rotating the adjacent wheel by
one digit. This machine was capable of performing addition and subtraction
only supporting as many as 8 digits while multiplication and division operations
were done by repeated addition and subtraction respectively. A programming
language “Pascal” was later named to honour his contribution.

Stepped Reckoner
Gottfried Wilhem Von Leibniz, a German mathematician and philosopher, invented
a digital mechanical calculator called Stepped Reckoner in 1694. It consisted
of additional sets of wheels that could perform all four arithmetic operations:
addition, subtraction, multiplication and division. The machine was about 67
cm (26 inches) long, made of polished brass and steel, mounted in an oak case.
Pascal’s and Leibniz’s devices were the forebears of today’s desktop computers.

Jacquard’s Loom
Joseph-Marie Jacquard, a French inventor, developed the Jacquard loom in
1801. It enabled production of fabrics with intricate woven patterns. He used a
punched card to control the movements of threads by the presence or absence
of holes in the card. The Jacquard loom started a technological revolution in the
textile industry, and the system of punched cards used in its operation became
a prototype for the first mechanical computers. The loom was declared public
property in 1806, and Jacquard was rewarded with a pension and a royalty on
each machine.

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Babbage’s Engines (Difference Engine and Analytical Engine)

Charles Babbage was a son of a banker called Benjamin
Babbage. He was a mathematician and professor
in Cambridge University in England. He designed
and built mechanical computing machines on the
principles that anticipated the modern electronic
computer. He designed an automatic mechanical
calculating machine called Difference Engine in 1823.
The Difference Engine was an automatic, mechanical
calculator designed to tabulate polynomial functions.

It was powered by steam. The Difference Engine
was an automatic, mechanical calculator designed
to tabulate polynomial functions. It was powered by
steam.

The project failed its test in 1833. Babbage then turned his attention to the
Analytical Engine in 1833. The basic design of Analytical Engine included:

• Input devices in the form of perforated cards containing operating instructions

• Store for memory

• Mill with control unit that allowed processing instructions in any sequence

• Output devices to produce printed result.

The analytical engine was designed but was never built by Babbage because
the technology of manufacturing exact technical parts was not well developed.
Thus the unavailability of the technical parts constrained the machine from
working. However, he was honoured as the father of computers as a result of his
contributions to the basic design of the computer.

Lady Augusta Ada Lovelace

Augusta Ada King, Countess of Lovelace is mainly
known for having written a description of Charles
Babbage’s early mechanical general-purpose
computer, the analytical engine. This was the first
time that the concept of computer programming
was suggested and historians have credited Lady
Ada as the first computer programmer. She was
born in 1815, in Middlesex (now part of London)
and died in London in 1852. In 1979, the US Defence
Department named a programming language ADA
in her honour.

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Tabulating Machine
Herman Hollerith, American inventor, invented a Tabulating Machine in 1887.
The purpose of the tabulating machine was to speed up the process of assimilating
census data into a usable form that would meet the needs of a country that was
experiencing a significant growth in population from one decade to the next.
In 1896, Hollerith founded the Tabulating Machine Company. Within twenty
years, this company merged with three others to form the Computing Tabulating
Recording Corporation. As the organization grew and diversified, another name
change occurred in 1924, when the company became known as IBM.

Harvard Mark I
Howard Aiken, an electrical engineer and physicist, designed the first automatic
electromechanical computer called Harvard Mark-I in 1937. The Mark-I was
completed in 1944. It was used by the US Navy for gunnery and ballistic
calculations. It was built using 7,65,000 components and hundreds of miles of
wire, amounting to a size of 51 feet in length, 8 feet in height, and 2 feet deep. It
had a weight of about 4500 kg. It was also known as the IBM Automatic Sequence
Controlled Calculator (ASCC). It is considered to be “the beginning of the era of
the modern computer” and “the real dawn of the computer age”.

Atanasoff Berry Computer
John Vincent Atanasoff and Clifford Berry at Iowa State University, built the
world’s first electronic digital computer, Atanasoff Berry Computer in 1937-38.
The vacuum tubes were used in this computer for storing and for arithmetic logic
functions. It was designed for solving systems of simultaneous linear equations.
It was used by military to compute ballistic data.

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Electronic Numerical Integrator and Calculator
J. P resper Eckert and John Mauchly at the University of Pennsylvania in
Philadelphia developed the first operational electronic digital computer, ENIAC
in 1946 for the U.S. Army. It used 18,000 vacuum tubes, weighed 30 tons and took
up 1,800 square feet. It was used to prepare artillery-shell trajectory tables and
perform other military and scientific calculations.

Electronic Discrete Variable Automatic Computer
John Mauchly and J.P. Eckert designed one of the earliest electronic computer
called Electronic Discrete Variable Automatic Computer (EDVAC) in 1946 and
started operating only in 1951. The EDVAC was a binary serial computer with
automatic addition, subtraction, multiplication, programmed division and
automatic checking with an ultrasonic serial memory, It included a magnetic tape,
a control unit, a dispatcher unit to receive instructions and direct them to other
units, a computational unit to perform arithmetic operations, a dual memory unit
and three temporary tanks. The computer had almost 6,000 vacuum tubes and
consumed 56 kW of power. It covered 490 ft²’b2 (45.5 m²’b2) of floor space and
weighed 17,300 lb (7,850 kg).

Electronic Delay Storage Automatic Calculator
Maurice V. Wilkes and his team at the university of Cambridge constructed
the first practical stored-program electronic computer called EDSAC in 1949. It
had 3,000 vacuum tubes and used 30 kilowatts of electric power. The computer
contained 32 mercury delay lines for memory with an access time of one
millisecond. Addition was done in 1500 microseconds and multiplication in 4000
microsecond. Standing six feet tall and in three long racks were the control and
arithmetic units. Programs were input using paper tape and output results were
printed on a teletype page printer.

Universal Automatic Computer-I
Universal Automatic Computer-I (UNIVAC-I) was the first commercial computer
produced in the United States. It was designed principally by John Mauchly and
J.P. Eckert. The UNIVAC-I was started in 1946 and completed in 1951. Magnetic
tapes were used as input and output mediums. It was used in Census Bureau in
early 1951 for taking census. It was also based on the EDVAC design. UNIVAC
I used 5,200 vacuum tubes, weighed 29,000 pounds (13 metric tons), consumed
125 kW, and could perform about 1,905 operations per second running on a 2.25
MHz clock. It was 8 ft high and 15 feet long.

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Apple

The Apple I, also known as the Apple-1, was an early
personal computer. It was designed by Steve Wozniak
and Steve Jobs. The Apple-I was the first product,
demonstrated in April 1976 at the Homebrew Computer
Club in Palo Alto, California.

IBM Personal Computer

The IBM Personal Computer, commonly known as
the IBM PC was introduced on August 12, 1981. It was
created by a team of engineers and designers under
the direction of Don Estridge of the IBM Entry Systems
Division in Baco Raton, Florida. It was a complete
system, with a built-in monitor, keyboard and data
storage.

Macintosh

Macintosh, or Mac, is a series of several lines of personal
computers designed, developed, and marketed by
Apple Inc. The Macintosh was introduced on January
24, 1984; it was the first commercially successful
personal computer to feature a mouse and a graphical
user interface rather than a command-line interface.

Pentium Processor

Pentium Processor is a family of 32-bit CPU chips from
Intel. Pentium chips have been the most widely used
in the world for general-purpose computing. It was
introduced on March 22, 1993. The last of the series
were the dual-core Pentium 4 models, and the Pentium
was superseded by the Core in 2006.

Gaming Computer 21

A gaming computer is a personal computer constructed
specifically to process the enormous amounts of data
required when playing massively multiplayer online
role-playing games (MMORPGs) and online first-
person shooter games. The computer usually comes
with a high-end graphics card, and the fastest central
processing units (CPUs) commercially available.

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Generations of Computers
Computer technology has undergone a series of transitions, each of which has
made computers increasingly easy to use, widening the range of problems
computers can solve. The development of the computer took place in five distinct
phases known as generations of computers. Each generation witnessed major
technological developments resulting in smaller, cheaper and more powerful
devices.
Let us examine each generation a little more closely and see their distinctive
features in short:

The First Generation (1946 to 1958)
First generation of electronic computers began with the
development of vacuum tubes as the internal electronic
components. The vacuum tubes required great amounts
of energy and generated much heat. They also burned
out easily and were hard to maintain. Vacuum tube was
developed by Lee DeForest in 1908.
The outstanding features of the first generation computers
are:
• The electronic circuitry was based on thermionic valves and vacuum tubes.
• They were restricted to commercial and scientific applications.
• The system cost and working cost were very high.
• They were relatively unreliable due to the failure of vacuum tubes and

heating problem.
• They were extremely large and occupied a very large space.
• The operating speed was limited to the milliseconds range.
The examples of first generation computers are Universal Automatic Computer
(UNIVAC), Electronic Numerical Integrator and Calculator (ENIAC), Electronic
Delay Storage Automatic Computer (EDSAC), BURROUGHS 220 and Electronic
Discrete Variable Automatic Computer (EDVAC).

The Second Generation(1959-1964)
The second generation computers were developed
during the second decade of the electronic computer
era (approximately 1959-1964). The second generation
of electronic computers began with the development of
the transistor (electronic switching device). The three
Bell Lab scientists’, John Burdeen, Walter Brattain, and
William Shockley, working for Bell Labs invented the
transistor in 1947 which won the Nobel Prize in 1956.

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22 Computer Studies-9

The outstanding features of second generation computers were:

• Vacuum tubes were replaced by transistors in their electronic circuitry.

• They were less expensive, smaller in size due to miniaturization of electronic
device.

• There was an overall reduction in system and operating costs.

• They required less electricity and emitted less heat than vacuum tubes.

• They were more reliable and accurate than the first generation computers.

• An increase in operating speed up to the microseconds range.
• Machine-independent “high level” programming languages such ALGOL,

COBOL, FORTRAN were introduced to simplify programming.
The examples of the second generations are IBM 1620, IBM 1401, Control Data
Corporation 3600, 400 series, LEO Mark III and IBM 7094.

The Third Generation(1965-1974)
The third generation brought huge gains in
computational power. The development of Integrated
Circuits (IC) signalled the beginning of the third
generation. Jack Kilby, an engineer with Texas
Instruments, developed the Integrated Circuit in 1958.
The features of third generation computers were:

• Transistors were replaced by Integrated Circuits in their electronic circuitry.

• Magnetic disks were used for auxiliary memory.

• The size of the computer became much smaller.

• Monitors and keyboards were introduced for data input and output
respectively.

• The reliability and accuracy of these systems improved and their MTBF went
up to several hundreds of hours.

• The speed of operation was improved to nanoseconds.

• They had a larger storage capacity.

• They were reliable and better in performance.

• A further development of high level language, including RPG (Report
Program Generator) and Pascal were introduced.

The examples of third generation computers are IBM system/360, National Cash
Register Century Series, ICL 1900 series, DATA GENERAL range and IBM 370
series.

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The Fourth Generation(1975-1990)
The fourth generation of computer system saw the use
of Large Scale Integration (LSI) that could fit hundreds
of components onto one chip and Very Large Scale
Integration (VLSI) squeezed hundreds of thousands
of components onto a chip in the construction of
computing elements. These developments were
followed by the creation of microprocessors. The first
microprocessor called Intel 4004 was developed by
American Intel Corporation in 1971.
The features of fourth generation computers are:

• Large Scale Integration (LSI), and later Very Large Scale Integration (VLSI),
are the advances that occurred in this generation.

• The computers were highly reliable and accurate.

• The operating speed was excellent, measured in picoseconds.

• A further refinement of input/output devices took place.

• Micro computers were introduced.

• Magnetic disk became the common source of external storage.

• Fourth Generation Language and application software for microcomputers
became popular.

The examples of this generation are IBM PC, Apple/Macintosh, HP3000 and the
SUPERBRAIN.

The Fifth Generation (After 1991 and Beyond)
The fifth generation computers were invented after 1991. This generation is
marked by the evolution of computer that use newer, faster technologies to carry
out a broader variety of tasks. The fifth generation computer project conducted
jointly by several Japanese computer manufacturers under the sponsorship of the
Japanese government emphasized artificial intelligence, focusing on such matters
as machine reasoning and logic programming languages (e.g. Prolog).
The features of the fifth generation computers are listed below:

• The development of the fifth generation of computer system is characterized
mainly by the acceptance of parallel processing.

• These computers will use super conductor technology. The two future devices
are Gallium Arsenide (GaAs) chips and Biochips.

• These computers will have artificial intelligence.

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C Dompu- ictionary

Artificial Intelligence: A branch of computer science that refers to the use of
computer in such a way that they are able to reason and
draw, recognise voice and have language processing
ability.

Chip : A small slice of silicon material on which integrated
electronic components are deposited.

Capacitor : A device for storing an electrical charge.

Diode : An electronic device that allows the passage of current
in only one direction.

Logarithms : The exponent or power to which a stated number,
called the base, is raised to yield a specific number.

Resistor : Component of an electric circuit that resists the flow of
direct or alternating electric current.

Recap

• Abacus is one of the first mechanical calculating device created by the
Chinese.

• John Napier, a Scottish mathematician, developed the system of logarithms
in 1614 and a small instrument called Napier’s Bones in 1617.

• William Oughtred, an English mathematician invented Slide Rule in 1620.

• Blaise Pascal, a French philosopher, mathematician, and physicist, invented
the first mechanical adding machine called Pascaline in 1642.

• Charles Babbage, an English mathematician, made a working model of a
mechanical computer called Difference Engine in 1823 A.D. and Analytical
Engine in 1833 A.D. respectively.

• Lady Ada Lovelace is credited as the first computer programmer.

• Herman Hollerith, a census statistician, invented Tabulating Machine in 1887.

• Mark-I was the first automatic electromechanical computer designed by
Howard Aiken in 1937.

• John Vincent Atanasoff and his graduate student Clifford Berry, build the
first digital computer called Atanasoff Berry Computer in 1939.

• Intel developed the world’s first microprocessor called Intel 4004 in 1971.

• IBM introduced its first personal computer, the IBM PC, in 1981.

• First generation computers were powered by thousands of vacuum tubes as
their active electronic components.

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Computer Studies-9 25

Review Yourself

1. State whether the following statements are true or false.
a. William Oughtred invented a small instrument called Napier’s Bones in
1617.
b. Herman Hollerith designed an automatic mechanical calculating
machine called Difference Engine in 1823.
c. John Vincent Atanasoff and Clifford Berry at Iowa State University, built
ENIAC in 1937-38.
d. Pentium Processor is a family of 32-bit CPU chips from Intel.
e. The first microprocessor called Intel 4004 was developed by American
Intel Corporation in 1971.
f. The development of the fourth generation of computer system is
characterized mainly by the acceptance of parallel processing.

2. Fill in the blanks.
a. Blaise Pascal invented the first mechanical calculator called ___________
in 1642.
b. ___________________, a French inventor, developed the Jacquard loom
in 1801.
c. ______________was honoured as the Father of Computers as a result of
his contributions to the basic design of the computer.
d. Maurice V. Wilkes and his team at the university of Cambridge
constructed the first practical stored-program electronic computer called
__________ in 1949.
e. First generation of electronic computers began with the development of
______________ as the internal electronic components.
f. The development of the fifth generation of computer system is
characterized mainly by the acceptance of ___________.

3. Match the following.
Generation Description
First generation Artificial Intelligence
Second generation Vacuum Tubes
Third generation Transistors (Flip-Flops)
Fourth generation Integrated Circuits
Fifth generation Microprocessors

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26 Computer Studies-9

4. Give the full form of the following abbreviations.

a. ASCC b. ENIAC c. EDSAC d. UNIVAC e. EDVAC

5. Select the best answer from the list of choices.

a. William Oughtred, an English mathematician invented __________ in 1620.

i. Slide Rule ii. Pascalina iii. Stepped Reckoner

b. Gottfried Wilhem Von Leibniz, a German mathematician and philosopher,
invented a digital mechanical calculator called Stepped Reckoner
in____________.

i. 1694 ii. 1671 iii. 1823

c. _______________designed an automatic mechanical calculating machine
called Difference Engine in 1823.

i. Charles Babbage ii. Lady Ada iii. John Napier

d. Universal Automatic Computer-I (UNIVAC-I) was the first _____________
produced in the United States.

i. commercial computer ii. electronic digital

iii. earliest electronic computer

e. The _______________ was created by a team of engineers and designers
under the direction of Don Estridge of the IBM Entry Systems Division in
Baco Raton, Florida.

i. IBM Personal Computer ii Apple Computer

iii. Pentium Processor

6. Write date of invention and name of the inventor for the following devices.
a. Napier’s Bone
b. Slide Rule
c. Pascaline
d. Stepped Reckoner
e. Difference Engine
f. Tabulating Machine
g. Atanasoff Berry Computer

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7. Answer the following questions.
a. What is abacus? What are the features of abacus?
b. Who invented the slide rule? On what principle does it work?
c. What were the contributions of Blaise Pascal in the development of automatic

computation?
d. What invention led to the development of today’s computer? Discuss.
e. Who is the first female programmer in the history of computer? Why?
f. How did Joseph Jacquard contribute to the evolution of computer?
g. Explain the contribution made by George Boole.
h. Explain in short the contribution made by Herman Hollerith.
i. Name the first general purpose electronic digital computer designed for

commercial use? List any two features of this computer.
j. What do you mean by computer generation?
k. Name the electronic circuitry of the second generation computers.
l. What is an integrated circuit? Who invented it?
m. What is a microprocessor? Name the first microprocessor developed by

American Intel Corporation in 1971.
n. Describe the outstanding features of the first generation computers. What

were the shortcomings in the first generation computers?
o. How were the second generation computers an improvement over their

predecessors?
p. Discuss the major developments that took place in the fourth generation

computers.
q. What are the special features of fifth generation that makes it different from

the other generations?
r. Identify and name the following devices.

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28 Computer Studies-9

Chapter 3

COMPUTERS
FOR

EVERYONE

Objectives

After completing this chapter, you will be able to:
y Compare and contrast the different types of computers.
y Explain the difference between analog, digital and hybrid computers.
y Describe the classification of computers based on their size, cost, application areas

and computing power.

C Ooncept verview

A computer system is an electronic machine Computers
capable of accepting and processing data in a
fast, efficient and reliable manner. The different Analog Computers

types of computers are in use today due to the Digital Computers

continuing advances in computing technology. Super Computers

Computers are available in different shapes, sizes Mainframe Computers

and weights, due to these different shapes and Mini Computers

sizes they perform different sorts of jobs from one Micro Computers

another. They can also be classified in different Desktop Computers
ways. All the computers are designed by the Workstation
qualified computer architectures that design these

machines as their requirements. A computer that Portable Computers

is used in a home differs in size and shape from Laptops

the computer being used in a hospital. Computers Palmtops

are broadly divided into three groups on the basis Hybrid Computers

of computing techniques used. These are analog,

digital and hybrid computers.

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Computer Studies-9 29

Analog Computer

Analog computer is a computer in which continuously variable physical
quantities, such as electrical potential, fluid pressure or mechanical motion are
used to represent the quantities in the problem to be solved. It is a single problem
oriented machine. It is widely used in simulating the operation of aircraft, nuclear
power plants, and industrial chemical processes.

Examples:

Automobile speedometer

Thermometer

Digital Computer

Digital computer is an electronic computing machine that uses the binary digits
(bits) 0 and 1 to represent all forms of information internally in digital form.
Every computer has a set of instructions that define the basic functions it can
perform. Sequences of these instructions constitute machine-language programs
that can be stored in the computer and used to tailor it to an essentially unlimited
number of specialized applications. It can perform mathematical calculations,
organize and analyze data, control industrial and other processes, and simulate
dynamic systems such as global weather patterns.

It can be further classified according to their difference in size, cost, application
areas and computing power. They are as follows:

• Supercomputers • Mainframe computers

• Minicomputers • Microcomputers

Supercomputer

Supercomputer is extremely powerful computer capable of manipulating
massive amounts of data in a relatively short time. It has a highest computation
rate and largest memory. It has more than one CPU, often functioning in parallel
(simultaneously). It handles many thousands of operations simultaneously. It
is very expensive and are employed for specialized scientific and engineering
applications that must handle very large databases or do a great amount of

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computation. Supercomputer is used to design
automobiles, aircrafts and spacecrafts; to forecast
the weather and global climate; to design new
drugs and chemical compounds; and to make
calculations that help scientists understand the
properties of particles that make up atoms as
well as the behaviour and evolution of stars and
galaxies. Currently the fastest supercomputer
is the Cray Jaguar, at Oak Ridge National
Laboratory; it utilizes 224,162 processors to
execute potentially as many 1.759 quadrillion
mathematical operations per second.
Examples:
CRAY-1
CYBER 170/730

Mainframe computer
Mainframe computer is a high-speed performance computer with heavy use of
input/output units such as large-capacity disks and printers. It requires a strict
environmental condition of air, dust and temperature control. It can support
hundreds or thousands of connected users and can execute many programs
simultaneously. It acts as the central host computer in distributed data processing
systems. It is used for applications such as payroll computations, accounting,
business transactions, information retrieval, airline seat reservations, and
scientific and engineering computations.
Examples:
IBM 4300 series
IBM 1401

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Minicomputer
Minicomputer is a medium-sized computer. It is designed to meet the computing
needs for several people simultaneously in a small to medium size business
environment. It supports lesser connected users than a mainframe computer.
It has slower operation speed and lesser memory capacity than mainframe.
Mini computers are used in medium sized organization for the processing of
payrolls and financial accounts, cost handling, sales analysis and production
planning. They are commonly used as servers in network environments
that handle the data-sharing needs of other computers on the network.
Examples:
VAX 7500
Digital PDP-11

Microcomputer
Microcomputer is the smallest general-purpose computer system. It is a complete,
multi-use, electronic, digital computer system consisting of a microprocessor,
storage facilities, I/O ports, and a chip with megabytes of high-speed internal
storage. It can be used to analyze response to promotions, to perform word
processing and composition functions, to generate mailing labels, to assist with
graphic design, and so forth. Micro computers include the following types:

i. Desktop and Tower Models
Desktop model is a computer that fits

conveniently on the surface of a business
desk. A desktop computer’s main case
(called the system unit) is horizontally
oriented, which means that it can lie flat
on a desk or table. It is broad and low.
It is designed to be very small and are
sometimes referred to slimline model.
Tower model is a computer in which the
power supply, motherboard, and mass
storage devices are stacked on top of each
other in a cabinet. It sits vertically and
is often placed on the floor to preserve
desk space, allowing more room to place
external components, such as scanners
or printers, on the desk.

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32 Computer Studies-9

ii. Workstation

Workstation is a high-end microcomputer designed for technical or scientific
applications. It is intended primarily to be used by one person at a time, they
are commonly connected to a local area network and run multi-user operating
system. It is intended for business or professional use. Workstations and
applications designed for them are used by small engineering companies,
architects, graphic designers, and any organization, department, or
individual that requires a faster microprocessor, a large amount of random
access memory, and special features such as high-speed graphics adaptors.
Among the most successful makers of this kind of workstation are Sun
Microsystems, Hewlett-Packard DEC and IBM.

iii. Laptop

Laptop is a computer designed for mobile use and it is small and light
enough to sit on one’s lap while in use. It is a battery-or AC-powered personal
computer generally smaller than a briefcase that can easily be transported
and conveniently used in temporary spaces such as on airplanes, in libraries,
temporary offices, and at meetings. It has a smaller display, less memory, and
less storage space than a full-sized PC. A laptop typically weighs less than 5
pounds and is 3 inches or less in thickness.

iv. Palmtop

Palmtop computer is an ultraportable computer that literally fits in your
palm. It uses a pen to enter information. It uses small cards to store programs
and data. It has to be plugged into a main computer for other uses. It is
generally used for simple applications such as personal organizations and
note taking. Examples of Handheld PC devices are the NEC MobilePro 900c
and HP 320LX.

Hybrid Computer

Hybrid computer is a computer that employs both digital and analog quantities.
Hybrid computers use digital memory for the storage of intermediate results and
analog devices for computational purposes. They are special purpose machines.
They are generally used in the process control environment and for scientific
applications.
One example of a place you may find a hybrid computer is in the medical field
or centers. This helps lessen the overall time needed for data processing. Another
example of computer people are calling hybrid is a laptop mixed with a tablet.
This means that a person can use a laptop, but if they need to take it someplace,
they have the ability to remove it from the keyboard and use it as a tablet.

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C Dompu- ictionary

Analog computer : A computer that operates on data by measuring
changes in continuous physical variables such as
voltage, resistance and rotation.

Digital computer : A computer capable of solving problems by processing
information in discrete form.

Hybrid computer : A computer which combines the best features of both
analog and digital computers.

Super computer : A powerful computer capable of manipulating massive
amounts of data in a relatively short time.

Mainframe : A high-speed performance computer with heavy use
of input/output units such as large-capacity disks and
Recap printers.

• A computer system is an electronic machine capable of accepting and
processing data in a fast, efficient and reliable manner.

• Analog computer is a computer in which continuously variable physical
quantities, such as electrical potential, fluid pressure or mechanical motion
are used to represent the quantities in the problem to be solved.

• A digital computer is an electronic computing machine that uses the binary
digits (bits) 0 and 1 to represent all forms of information internally in digital
form.

• Supercomputer is extremely powerful computer capable of manipulating
massive amounts of data in a relatively short time.

• Mainframe computer is a high-speed performance computer with heavy use
of input/output units such as large-capacity disks and printers.

• Minicomputer is a medium-sized computer basically developed for use in
process control systems.

• Microcomputer is the smallest general-purpose computer system.

• Workstation is a high-end microcomputer designed for technical or scientific
applications.

• A desktop computer’s main case (called the system unit) is horizontally
oriented, which means that it can lie flat on a desk or table.

• Tower model is a computer in which the power supply, motherboard, and
mass storage devices are stacked on top of each other in a cabinet.

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34 Computer Studies-9

Review Yourself

1. State whether the following statements are true or false.

a. Analog computer is a multi-problem oriented machine.

b. A digital computer is an electronic computing machine that uses the
binary digits (bits) 0 and 1 to represent all forms of information internally
in digital form.

c. IBM 4300 series is an example of supercomputer.

d. Mainframe computer was basically developed for use in process control
systems.

e. Laptop is a computer designed for mobile use and it is small and light
enough to sit on one’s lap while in use.

f. Palmtop is a computer that employs both digital and analog quantities.

2. Match the following.

Minicomputer Extremely powerful computer capable of
manipulating massive amounts of data in a
relatively short time.

Microcomputer A high-speed performance computer with
heavy use of input/output units such as large-
capacity disks and printers.

Mainframe A medium-sized computer basically developed
for use in process control systems.

Supercomputer A complete, multi-use, electronic, digital
3. Fill in the blanks. computer system consisting of a microprocessor,
storage facilities, I/O ports, and a chip with
megabytes of high-speed internal storage.

a. ____________ computer is a computer in which continuously variable
physical quantities are used to represent the quantities in the problem to
be solved.

b. ____________ has more than one CPU, often functioning in parallel
(simultaneously).

c. _______________ computer is a high-speed performance computer
with heavy use of input/output units such as large-capacity disks and
printers.

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Computer Studies-9 35

d. ___________ model is a computer in which the power supply,
motherboard, and mass storage devices are stacked on top of each other
in a cabinet.

e. A ____________typically weighs less than 5 pounds and is 3 inches or
less in thickness.

f. _____________ computer is a computer that employs both digital and
analog quantities.

4. Give the answer in one word.
a. A computer that operates on data by measuring changes in continuous
physical variables such as voltage, resistance and rotation.
b. A computer which combines the best features of both analog and digital
computers.
c. A high-speed performance computer with heavy use of input/output
units such as large-capacity disks and printers.
d. A computer that fits conveniently on the surface of a business desk.
e. A high-end microcomputer designed for technical or scientific
applications.
f. A computer designed for mobile use and it is small and light enough to
sit on one’s lap while in use.

5. Answer the following questions.
a. What is an analog computer? Give any two examples.

b. What is a digital computer? What are the two types of digital computers?
Explain them in short.
c. What are super computers and where are they used?
d. What is a mainframe and what are its typical applications?
e. What is a minicomputer? Where is it used?
f. What is a microcomputer? List the different types of microcomputer.
g. Differentiate between desktop model and tower model.
h. What is a laptop computer?
i. What is a palmtop computer?
j. What is a hybrid computer?

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Chapter 4

ANATOMY OF
COMPUTER
SYSTEM

Objectives

After completing this chapter, you will be able to:
y Explain the main functions of a computer system.
y Explain the different functions of a CPU.
y Compare and contrast the different types of computer memory.
y Explain the function of motherboard, microprocessor, expansion slots and computer

power supply units.

C Ooncept verview

A computer system is a combination of various components that work together
to accomplish one or more common goals. It is typically equipped with four
important components namely input devices, process unit, memory unit and
output devices. Each device performs a precisely specified task, and are connected
to form a complete computer. 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.
A computer system performs the following functions:
• Receives input in the form of data and instructions
• Processes the data on the basis of the instructions
• Displays the processed data as output
This cycle of operation of a computer is referred to as the Input-Process-Output
cycle or the IPO cycle.
A typical computer system consists of the following functional components to
accomplish the above task:
• Input devices
• Central Processing Unit
• Output devices

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Input Devices
Input device is a peripheral device that is used to enter data and instructions into
a computer. It converts these data and instructions into electrical signals that are
recognized by the computer. It acts as a communication channel between the
user and the computer.
Input devices perform the following basic functions:
• Accept data from the outside world.
• Convert data into binary code that is understandable to the computer.
• Send data in binary form to the computer for further processing.
A large variety of input devices are available, but the most commonly used input
devices are keyboard, mouse, tracker ball, touch sensitive pad, joystick, light pen,
bar code reader, microphone, digital camera and scanner.

Central Processing Unit
Central Processing Unit is the main information processor in a computer. It is
a chip that functions as the “brain” of a computer. It interprets and carries out
instructions provided by the software. It tests and manipulates data, and transfers
information to and from other components, such as the working memory,
disk drive, monitor and keyboard. The central processing units of personal
computers are generally implemented on a single chip, called a microprocessor.
The processing capability of a PC is measured in terms of the amount of data
processed by its CPU in one operation. The speed of the CPU is measured in
MegaHertz (MHz).
The various types of CPU chips are Pentium 4 Dual Cores, Pentium 4 and Celeron.
The three important components of a central processing unit are:
• Arithmetic and Logic Unit (ALU)
• Control Unit (CU)
• Primary Memory

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Arithmetic and Logic Unit
ALU acts as one of the prime units of computer. It is the place where all arithmetic
calculations and other logical operation takes place. It contains the accumulator,
the temporary register, logical and arithmetic circuits.
Control Unit
The control unit is the nerve centre of the computer. It regulates and integrates the
operations of the computer. The control unit functions in fetch-decode-execute
cycle. It fetches the instructions and data from the main memory, decodes them
and sends them to the ALU. The output from the ALU is fetched by the control
unit and sent to various parts of the computer.
Primary Memory
Primary memory is the internal memory system within the computer that stores
the unprocessed and processed data as well as the program instructions. It is
contained on computer chips and uses electronic circuits to store information.
It is primary since it is the only memory from which the computer can access
information directly and process it. The primary memory of a computer system
is made up of memory chips. There are two types of memory chips. They are:
• Random Access Memory
• Read Only Memory

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Random Access Memory
Random Access Memory is the most important form of memory in which specific
contents can be accessed (read or written) directly by the CPU in a very short time
regardless of the sequence (and hence location) in which they were recorded. The
information stored in the RAM is temporary and volatile because the moment
another program is fed in it, the initial program stored in those memory location
gets erased. The data in RAM stays there only as long as your computer is
on, and electricity is flowing through the machine. Increasing RAM improves
system performance. The most common form of RAM, in use today, is built from
semiconductor integrated circuits, which can be either static (SRAM) or dynamic
(DRAM).

i. SRAM (Static Random Access Memory)
In a static RAM, binary values are stored using

traditional flip-flop logic gate configurations.
If the power is maintained then depending on
the type of transistors used, data can be stored
indefinitely without degradation. Static RAM has
a low bit density, high power consumption and is
more expensive.

ii. DRAM (Dynamic Random Access Memory)
DRAM is made with cells that store data as charge on capacitors. The

existence of charge in a capacitor is interpreted as a binary 1 or 0. Due to
leakage, the capacitor discharges gradually and the memory cell loses the
information. Therefore, to preserve the information, the memory has to be
refreshed periodically. Despite this inconvenience, DRAM is a very popular
memory technology because of its high density and consequent low price.

Read Only Memory
Read Only Memory is “built-in” computer memory containing data that normally
can only be read, not written to. ROM contains the programming that allows your
computer to be “booted up” or regenerated each time you turn it on. Unlike a
computer’s random access memory (RAM), the data in ROM is not lost when the
computer power is turned off. The ROM is sustained by a small long-life battery
in your computer. There are numerous ROM chips located on the motherboard
and a few on expansion boards. The chips are essential for the basic input/output
system (BIOS), boot up, reading and writing to peripheral devices, basic data
management and the software for basic processes for certain utilities.

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40 Computer Studies-9

i. Programmable Read Only Memory (PROM)

Programmable read-only memory (PROM) or one-time programmable ROM
(OTP) can be written to or programmed via a special device called a PROM
programmer. Typically, this device uses high voltages to permanently destroy
or create internal links (fuses or antifuses) within the chip. Consequently, a
PROM can only be programmed once.

ii Erasable Programmable Read-Only Memory (EPROM)

Erasable programmable read-only memory (EPROM) can be erased by
exposure to strong ultraviolet light (typically for 10 minutes or longer),
then rewritten with a process that again requires application of higher than
usual voltage. Repeated exposure to UV light will eventually wear out an
EPROM, but the endurance of most EPROM chips exceeds 1000 cycles of
erasing and reprogramming. EPROM chip packages can often be identified
by the prominent quartz “window” which allows UV light to enter. After
programming, the window is typically covered with a label to prevent
accidental erasure. Some EPROM chips are factory-erased before they are
packaged.

iii. Electrically Erasable Programmable Read-Only Memory (EEPROM)

Electrically erasable programmable read-only memory (EEPROM) is based
on a similar semiconductor structure to EPROM, but allows its entire contents
(or selected banks) to be electrically erased, then rewritten electrically, so that
they need not be removed from the computer (or camera, MP3 player, etc.).
Writing or flashing an EEPROM is much slower (milliseconds per bit) than
reading from a ROM or writing to a RAM (nanoseconds in both cases).

Cache Memory

Cache memory is a temporary computer storage
used for quick retrieval of data in order to increase
processing speed. The cached data can be stored in a
reserved area of RAM, a special cache chip (separate
from the CPU) that provides faster access than RAM,
or on the disk drive. By keeping frequently accessed
data in a rapidly accessible place, the computer can
respond quickly to requests for those data without
having to perform time-consuming searches of RAM
or hard drives. Since a “stale” cache will contain data
that have been superseded by later information, the
cached data must be refreshed periodically.

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Secondary Memory
The secondary memory is a long-term memory used
to store programs and data for the future reference.
It supplements the limited storage capacity and the
volatile characteristics of primary memory. This is
because secondary memory is much cheaper than
primary storage, and the data or programs stored in
secondary memory will not be lost when electrical
power is switched off. It is also known as backing
storage or external memory. The two main types of
secondary memory are magnetic disk and optical disk.

Output Devices
Output device is a peripheral device that is responsible for displaying the
output. It receives information from the computer and translates it from machine
language to a form that human can understand.
An output device performs the following functions:
• Accepts results produced by the computer in binary coded form.
• Converts the binary coded data into human acceptable form.
• Supplies converted results to the outside world.
The monitor, printer and plotter are some of the popular output devices. Output
sent to a monitor is called soft copy while output sent to a printer is called
hardcopy.

Monitor

Printer

Inside the System Unit
A system unit is the main computer cabinet housing containing the primary
components of the system. The system unit case is typically a metal chassis that
contains the basic parts of the computer system. The system unit includes the
chassis, microprocessor, main memory, bus, and ports, but does not include the
keyboard or monitor, or any peripheral devices. In this section, you shall learn
some of the important parts of a PC system.

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Motherboard

Motherboard is the “back bone” of the
computer. It is the primary printed circuit
board in a computer or other electronic
device. The motherboard serves to connect
all the parts of a computer together. The
CPU, memory, hard drives, optical drives,
video card, sound card and other ports
and expansion cards all connect to the
motherboard directly or via cables. The
motherboard is sometimes alternatively
known as the main board or system board.

Expansion slots and cards

Expansion slot is an opening in a computer where a circuit board can be inserted
to add new capabilities to the computer. It allows the computer system to
communicate with the outside world. Almost all personal computers except
portables contain expansion slots for adding more memory, graphics capabilities,
and support for special devices. The board inserted into the expansion slots
are called expansion cards. Expansion cards are also called “expansion boards,”
“controller cards,” or “adaptors”. The primary purpose of an expansion card is
to provide or expand on features not offered by the motherboard. The different
kinds of expansion cards are graphics card, modem, sound card and network
card. A USB expansion card is mainly used by users who need additional USB. A
PC expansion card can only be inserted on computers with available expansion
slots.

Microprocessor

Microprocessor is a device that integrates
the functions of the central processing
unit (CPU) of a computer onto one semi-
conductor chip or integrated circuit (IC).
It is contained within a cartridge that
plugs into the system board. It contains
the core elements of a computer system,
its computation and control engine.
A microprocessor consists of multiple
internal function units. A basic design has
an arithmetic logic unit (ALU), a control
unit, a memory interface, an interrupt or
exception controller, and an internal cache.

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Expansion ports
Expansion port serves as an interface between the computer and other computers
or peripheral devices. Physically, a port is a specialized outlet on a piece of
equipment to which a plug or cable connects. Electronically, the several conductors
making up the outlet provide a signal transfer between devices.
Electronically, hardware ports can almost always be divided into two groups
based on the signal transfer:
• Serial ports send and receive one bit at a time via a single wire pair.
• Parallel ports send multiple bits at the same time over several sets of wires.
Plug-and-Play ports are designed so that the connected devices
automatically start handshaking as soon as the hot-swapping is done. USB
ports and FireWire ports are plug-and-play.

Computer Power Supply Unit
The computer power supply unit is the component that supplies power to the other
components in a computer. More specifically, a power supply unit is typically
designed to convert general purpose alternating current (AC) electric power
from the main power supply. It also regulates the voltage to eliminate spikes and
surges common in most electrical systems. Not all power supplies, however, do
an adequate voltage-regulation job, so a computer is always susceptible to large
voltage fluctuations. Power supplies are rated in terms of the number of watts
they generate. The more powerful the computer, the more watts it can provide to
components.

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C Dompu- ictionary

ALU : Part of CPU where mathematical and logical operations
are performed.

Bus : Part of a chip or circuit board designed to send and
receive data. The bus on a computer’s motherboard
contains slots for expansion cards.

CPU : The brain of the computer which controls all the
activities of the computer.

CU : The nerve centre of the Central Processing Unit that
directs the physical operation of the computer system.

Cache memory : Memory that holds frequently accessed data or
program instructions for the purpose of speeding a
Recap computer system’s performance.

• A computer system is a set of various functional components of a computer
that are interconnected in some fashion to achieve the basic function of the
computer, that is to execute programs.

• An input device converts incoming data and instructions into a pattern of
electronic signals in binary code for acceptance by the computer.

• CPU is the computing part of any digital computer system, generally composed
of the primary memory, control unit and arithmetic-logic unit.

• ALU is the place where all arithmetic calculations and other logical operation
takes place.

• The control unit is responsible for execution of instructions.

• Primary memory is the internal memory system within the computer that
stores the unprocessed and processed data as well as the program instructions.

• Random Access Memory is the most important form of memory whose “bytes”
or memory locations are open and accessible to the user.

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

• Cache memory is a small, high-speed memory system that temporarily stores
frequently used instructions and data for quicker processing by the central
processor of a computer.

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Review Yourself

1. State whether the following statements are true or false.


a.
The processing capability of a PC is measured in terms of the amount of
data processed by its CPU in one operation.

b. The Arithmetic and Logic Unit is the nerve centre of the computer.

c. Primary memory is the only memory from which the computer can
access information directly and processes it.

d. DRAM has a low bit density, high power consumption and is more
expensive.

e. Erasable programmable read-only memory (EPROM) can be erased by
exposure to strong ultraviolet light.

f. The motherboard serves to connect all the parts of a computer together.

2. Match the following.

RAM Part of CPU where mathematical and logical
operations are performed.

Cache memory The nerve centre of the Central Processing Unit that

directs the physical operation of the computer

system.

ALU The brain of the computer which controls all the
activities of the computer.

CPU Memory that holds frequently accessed data or
program instructions for the purpose of speeding
up the performance of a computer system.

CU Semiconductor-based memory that can be read and

written by the microprocessor or other hardware

devices.

3. Fill in the blanks.

a. _____________ is a peripheral device that is used to enter data and
instructions into a computer.

b. The central processing units of personal computers are generally
implemented on a single chip, called _______________.

c. ____________ regulates and integrates the operations of the computer.

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46 Computer Studies-9

d. ____________ is “built-in” computer memory containing data that
normally can only be read, not written to.

e. ____________ is a temporary computer storage used for quick retrieval
of data in order to increase processing speed.

f. _______________ is the primary printed circuit board in a computer or
other electronic device.

4. Give the answer in one word.

a. Part of a chip or circuit board designed to send and receive data.

b. The brain of the computer which controls all the activities of the
computer.

c. The internal memory system within the computer that stores the
unprocessed and processed data as well as the program instructions.

d. A temporary computer storage used for quick retrieval of data in order
to increase processing speed.

e. A device that receives information from the CPU and present it to the
user in the desired form.

f. The primary printed circuit board in a computer or other electronic
device.

g. An opening in a computer where a circuit board can be inserted to add
new capabilities to the computer.

5. Select the best answer from the list of choices.

a. The nerve centre of the computer that regulates and integrates the
operations of the computer.

i. ALU ii. CU iii. PM

b. A computer main memory in which specific contents can be accessed
(read or written) directly by the CPU.

i. RAM ii. ROM iii. Cache memory

c. A temporary computer storage used for quick retrieval of data in order
to increase processing speed.

i. RAM ii. ROM iii. Cache memory

d. A device that integrates the functions of the central processing unit
(CPU) of a computer onto one semi-conductor chip or integrated circuit
(IC).

i. Motherboard ii. Microprocessor iii. Port

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e. An opening in a computer where a circuit board can be inserted to add
new capabilities to the computer.
i. Expansion slot ii. Expansion card iii. Expansion port

f. The component that supplies power to the other components in a
computer.
i. Power Supply Unit ii. Expansion card iii. Expansion port

6. Write the full form of the following abbreviations.

a. CPU b. ALU c. SRAM d. EEPROM
e. CU f. ROM g. DRAM h. EPROM

7. Answer the following questions.
a. What do you understand by the following terms:
i. Input device
ii. Central Processing Unit
iii. Output device
b. What is a system bus?
c. What is CPU? What are the different sections of CPU?
d. What do you understand by the Fetch-Decode-Execute cycle?
e. What is the function of control unit?
f. What is the function of primary memory? What are the two types of
primary memory?
g. Define the term “volatile” in the context of computer memory. Which
memory is known as volatile memory?
h. State the differences between EPROM and EEPROM.
i. What is cache memory? What is its advantage?
j. State the functions of output device.
k. What is a motherboard? What is the function of motherboard?
l. What is an expansion slot? What is the purpose of an expansion slot?
m. What is a computer power supply?

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Chapter 5

INPUT AND
OUTPUT DEVICES

Objectives

After completing this chapter, you will be able to:
y Explain the uses of different input devices.
y Explain the uses of different output devices.
y Explain the difference between soft copy output and hard copy output.
y Identify and compare the two types of printer.

C Ooncept verview

A computer system can be useful, only when it is able to communicate with its
external environment (its users). The input/output (abbreviated I/O devices)
provide the means of communication between the computer and the outer world.
I/O (input/output) describes any operation, program or device that transfers
data to or from a computer. There are various devices used to enter information
and instructions into a computer for storage or processing and to deliver the
processed data to a human operator. I/O devices are used by a person (or other
system) to communicate with a computer. Such devices comprise the peripheral
equipment of modern digital computer systems. Peripheral can be internal
(installed inside the computer) or external (existing outside the computer but
connected electronically to it). These devices form the essential link between
the user of the computer system and the computer system itself. The interaction
between the input and output hardware is controlled by software called the Basic
Input Output System software (BIOS).

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Input Devices

Input is the action of collecting raw-data at the beginning of a computer-based
information system into a form that is usable by the computer for processing.
The raw-data and program are entered into the computer through input device.
It reads the raw-data prepared by the user and sends them into the computer
as a series of electronic pulses. The input devices establish the communication
link between the user and the computer system. Some examples of input devices
include:
• Computer keyboard
• Computer mouse
• Touchpad
• Trackball
• Image scanner
• Webcam
• Barcode scanner
• Video capture/tuner card
• Microphone

Bus Cable

I Processor M Computing O
N sends to E by U
P memory for M T
U storage O processor P
T R U
Y T

Flow of information

Computer Keyboard

Computer keyboard is the primary text input device. It enables the user to
enter data directly into the computer. The computer keyboard uses the same
key arrangement as the mechanical and electronic typewriter keyboards. The
standard arrangement of alphabetic keys is known as the Qwerty (pronounced
KWEHR-tee) keyboard, its name deriving from the arrangement of the five keys
at the upper left of the three rows of alphabetic keys. Standard keyboard contains
alphabetic characters, punctuation symbols, numbers and a variety of function
keys.

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