Introduction to Information and Communication Technology

Chapter one
1. An overview of information and communication technology
1.1What is IT and what is ICT?
Information Technology (IT) Is modern technology that used to capture, process, store, retrieve,
and communicate data or information in the form of numerical data, text, sound, or image.

Information and Communications Technology (ICT) refers to the use of computers and
telecommunications network to create, store, process, send, and receive information from anywhere,
anytime. Hence, it refers to both computer and communication technologies

 ICT is the study of information handling and its use in society by means of modern
technology. This includes the acquisition, processing, storage and communication of
information in any form by appropriate means
1.2 Components of ICT.
Information and communication technology is divided into three primary components. These are
 Computers,
 Communications networks, and
 Know-how.
1. Computers
 Computer, in simple terms, is an electronic machine that can be instructed to accept, process,
store, and present data and information
 Computer is a device that enables you to process information automatically and in
accordance with instructions that you give it.
 Computers have become part of the day-to-day activities of people around the globe. It is
difficult to think any field that does not involve or is not affected by computers.
2. Communications network
• An integral part of IT is the ability to communicate: to send and receive data and information
over a communication network.
• A communications network is the connection of stations at different locations through a
medium that enables people to send and receive data and information.
Example: Telephone wires and cables are common communication media.
Data communication is the transmission of data and information over a communications medium.
3. Know-how
Although computers and data communication are very important parts of IT, an equally
critical part of IT is the ability to draw on the power of IT to solve problems and to take advantages
of the opportunities it creates. Therefore it requires or implies know-how, knowing how to do
something well. Know- how includes:
• Familiarity with the tools of IT
• The skills needed to use these tools
• Understanding when to use IT to solve a problem

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1.3 Functions and Application of IT

1.3.1 Functions of IT
Information technology using computers has the following functions:
A. Capture
 It is often useful to compile detailed records of activities.
 Data capture is performed when IT users expect the data to be useful later.
Example:
 When a book is checked out of the library, the name & Id. No. of the borrower, the title,
author & call number of the book is captured.
 A doctor records the pulse, heart rate, and WBC count of hospital patients.
 The voice and data recorders in aircraft cockpits capture the pilot's conversations and record
flight data about the aircraft’s location and performance.
B. Processing
 Is most often associated with computers?
 Is the main reason to buy computers
 Entails converting, analyzing, computing and synthesizing all forms of data or information.
 Information/data may come in different forms
 Text, reports, correspondence, sound, voice, music, images, visual information (charts,
graphs, drawings etc.)

Multimedia systems
 Are systems that process multiple types of information simultaneously? Other types of
processing are:

Word processing
 Word processing is the creation of text-based documents, including reports newsletter etc.
Image processing
 It is converting visual information (graphics, photos, etc.) Into a format that can be managed
within a computer system.
a process called scanning converts a print or film image into a form that a computer can use.
Voice processing: - Is the processing of spoken information.

C. Generation
 Generating information means organizing data & information into a useful form whether as
text, sound or image.
D. Storage and Retrieval
 Through information storage, computers keep data and information for later use.
 Stored data & information all placed in a storage medium that the computer can read.

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 Retrieval entails locating and copying stored data or information for further processing or
for transmission to another user.
E. Transmission
 The sending of data or information from one location to another
 Modern communications networks enable us to send information down the hall or around the
world in an instant.
1.3.2 Application of IT
The main areas of applications can be listed as follows:
In education
As learning aids
Example: learning toys, programs range from simple arithmetic to calculus, from English grammar
to creative writing and foreign language, and from basic graphics to engineering design models,)
In educational activities on the other hand, computers can be used in educational activities
to assist both the learner and the teacher. Computer-Assisted Instruction (CAI) helps the learning-
teaching process in schools and colleges. Computers can be used to deliver lectures using
presentation software. Computers can also be used in educational administration such as:
• Keeping records of students,
• Keeping inventories of books in the library, text books, chemicals in the laboratory and
safety information, and other instructional materials,
• Setting timetables for subjects, and
• Delivering lectures.
An important application of computers in the education sector is distance education, also called
distance learning (e-learning).
Distance Learning is a method of teaching in which students are not required to be physically
present in a school or a university.
Written material, videos, audiotapes, and CD-ROMs are sent to the student. The student sends back
answers to exercises and assignments. Nowadays the internet can be used for distance learning.
Websites can be set up with information for the learner and e-mail can be used to communicate with
a tutor.
Entertainment:
Examples: games, films etc.
Commercial or business applications
Computers are needed to perform business operations that require handling large amounts of data.
Several computer applications are available to assist business in working with large volumes of data.

Examples are:
 Text processing
 Accounting and finance management
 Inventory control
 Database management
 Statistical analysis

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Scientific – engineering and research applications

Using computers for scientific research, complex mathematical calculations, design work,
and analysis and control of physical systems.

Examples are:
 Space technology
 Meteorological observatory systems
 Astronomical investigations
 Design of machines and
 Control of manufacturing process
Electronic banking and service:
Example: teller machine (customers are issued cards that permit them to use other banks teller
machine’s)
Online banking (a bank customer can use his/ her computer to check account balances, transfer
funds, pay bills)
Shopping from home
Individual may now shop by computer in the comfort of their home.
Household control
A growing number of the newer houses hold devices are computers controlled. For example:
security systems, refrigerators, microwave ovens, washers, stereos, and televisions. This computer
controlled home security system monitors movements, broken glass, unlawful entry without a
security code, and so on, and alerts the local police department.
Weather and environment
Computer equipment may show temperature ranges , precipitation levels and wind flow and can
used in weather forecasting. Computer can also helped in overcoming environmental hazards.
Transportation
Computers have affected almost every kind of transportation. Many aircraft can fly under the control
of the computer; in this situation, the captain simply serves as a manger by telling the computer what
to do. In cars, computers have provided functional controls such as spark and fuel control.
Medical and Health care
Computers have long been used by hospitals for routine record keeping. Today, however, many
people owe their lives to the computer. Computers are used in hospitals as sensors (device that detect
changes in blood pressure, heart rate, temperature), testing (scan the body and provide 3-d figure),
patient treatment.
Routine and dangerous tasks
Computers are used in routine tasks. And they can perform task in environments to dangerous for
human workers.
Example: Consultant (expert system)

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An expert system is a computer program, which can solve problems from a specific knowledge base.
These systems don't replace expert humans because the knowledge base of expert system is given
from the skilled specialist.
Example: mycin (a medical diagnostic program by using sophisticated decision making process).

1.4 Data processing

Data processing is the handling of data and transforming them into information. It is the process of
converting data into information.
E.g. calculating the balance in a check book.
Data processing can be done manually, where brain, paper, and pencil are used. It can be done with
the aid of electro-mechanical devices such as a calculator. It can also be done electronically using a
computer as a tool. In the rest of this note, data processing is assumed to be done using computers.

The objective of data processing is “getting the right information to the right person at the right
time”. Hence, if the information is to be valuable, a data processing system must meet some criteria:
Accuracy: The individual steps in the processing of data must be accurate.
The input data to the processing system must also be accurate.
There is a saying “GIGO or Garbage In, Garbage Out” to express that wrong input data generate
wrong and useless results.
Timeliness: The right information delivered too late can be as useless as no information at all, i.e.,
the data processing system has to be fast.
Meaningfulness: The information produced by the data processing system must be meaningful to
the people using the information. i.e.
 The information must be appropriate and relevant to the user’s needs.
 The report presented must be compressible. Both the format and the content of the report
must be easy to read and understand.
Basic data processing activities:
1. Data collection: data processing activity that involves getting data from the origin to the system.
2. Data recording: the process of expressing data in a form that is recognizable by either a person
or a machine.
3. Data classification: a process of categorizing all items of data according to common
characteristics and features.
4. Data sorting: the arrangement of data items in a desired sequence.
5. Data store: retaining the data for future reference.
6. Retrieving data: refers to finding a specific stored data.
7. Summarizing data: is the process of condensing data.
8. Data communication: distributions of information to the specific end users.

1.4.1 Data processing cycle

As defined earlier, data processing is the process of converting data into information. It involves
three steps: input, processing, and output as shown in the following figure.

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Input Processing Output

In general, a computer gets input through an input device such as a mouse or a keyboard, processes it
according to the set of instructions given to it, and generates an output.
1. Input: refers to anything that is given to a computer for processing. It may take various forms
such as numbers for calculation, text to be printed, etc.
2. Processing: the computer has to be told what to do with the input. That means a computer must
be programmed with the set of instructions it is required to perform.
3. Output: refers to the result of data processing such as a printed text. Once the computer
processes the input using the instructions given to it, it produces an output using an output device
such as a screen or a printer. The output may take different forms. It may be a printout of the results
of students, playing music using speakers attached to the computer, etc.

As discussed earlier, one of the criteria for a data processing system is accuracy of the result. This in
turn requires input data accuracy. When data is given as input to the computer, we have to make sure
that it is correct and meaningful so that the result or the output of the data processing is also
meaningful. Ensuring data accuracy means the input data is not in any way wrong. This can be done
using two techniques: data verification and data validation
1.4.2 Data verification and validation
Data verification and validation are checks to make sure that data entered into a computer is
accurate.

When entering data onto a system it is important that this data is accurate. There is a term in
computing: Garbage In, Garbage Out (GIGO). What this means is that if you put wrong
information into a computer you will get wrong information out of a computer. Data verification and
validation have been developed to make sure that the data entered is accurate

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CHAPTER TWO
2. Evolution and Types of computers
2.1 History and Development of computers
What is computer?
The term computer is derived from the word ‘compute’, which means to calculate. Therefore, a
computer can be defined as an electronic machine, devised for computing calculations and
controlling operations that can be expressed in logical or numerical terms. It is an electronic device
that performs diverse operation with the help of set of instructions, called a program, to process the
information in order to achieve desired results. In other words, a computer is an electronic data
processing machine that’s designed and organized to automatically accept and store data, process
them, and produce output under the direction of a stored detailed step-by-step set of instructions.
Data processing consists of gathering raw data input, evaluating and bringing order to the data, and
placing it in proper perspective so that useful information will be produced. From this definition it
can be inferred that data are raw materials on which processing is carried out and information are
processed outputs. Hence, in very brief terms, a
computer is a data processing device that converts raw data (facts and figures) into useful
information that give meaning to the user.

Programs usually reside within the computer and are retrieved and processed by the computer’s
electronics. The program results are stored or routed to output devices, such as video display
monitors or printers. Computers perform a wide variety of activities reliably, accurately, and
quickly.
The computer technology, being the youngest and the most dynamic industry evolved and dominated
the world in nearly half a century. However, this legendary machine – the computer – had to pass
through a series of development phases to attain its contemporary form and marvelous capabilities.
Each phase of development, referred to as generation, is identified by a number of achievements and
electronic building blocks.

The constituent electronic devices used to construct the machine were one of the criteria used to
classify computers in a series of development phases. Different electronic elements were used in
each phase to obtain improvements in four major areas; namely,
 Reducing cost
 Reducing size
 Increasing speed and
 Improving reliability
To date, four generations have been experienced and the fifth is being awaited for.
Different authors classify these generations in a slightly varying time frame. However, the following
reasonable time frame has been adopted for the purpose of this course.

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The First Generation (1945-1959)

The first generation computers used vacuum tubes as their key electronic component. Electronic
vacuum tube computers were much faster than their electromechanical counterparts of that time.
However, they had a number of drawbacks.
The following are the limitations of vacuum tubes. Vacuum tubes: -
 Are large in their very nature
 Consume a great deal of electricity
 Produce a lot of heat and
 Are prone to failure.

Thus, the computers constructed of these electronic components had the following inherent
problems. The machines:

 Were too big in size and hence very expensive

 Were very slow in function compared to today’s home computers.
 Were unreliable; the vacuum tubes were relatively short-lived and the computers had
difficulty operating continuously for more than a few hours at a time.
 Had high machine breakdown rate and faultfinding was very difficult
 Had high power consumption resulting in a very high running cost.

The most important representatives of this age are:

 ENIAC (Electronic Numerical Integrator And Computer, 1947)
 EDVAC (Electronic Discrete Variable Automatic Computer, 1949-1952)
 EDSAC (Electronic Delay Storage Automatic Calculator, 1949)
 UNIVAC (Universal Automatic Computer, 1951).

ENIAC was the first electronic general-purpose computer attributed to John W. Mauchly and
J.Presper Eckert. The machine was a major development on its own but has a number of defects. The
following points will help you visualize the machine:

 It occupied 15,000 square feet of floor space

 Weighed 30 tons
 It was purely electronic consisting of over 18,000 vacuum tubes and thousands of other
electronic components.
 It had such high power consumption that it dimmed the city of Philadelphia when it was
turned on.
 It had no means of storing program instruction in its memory; instead, the instructions were a
function of the way its electrical circuits were wired. If one needs to change the instruction,
one has to rewire the electrical circuits.

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EDVAC is an improved version of the ENIAC attributed to von Neumann, Mauchly and Eckert. The
central idea behind EDVAC was the “stored program” concept. The stored program concept states
that “The program as well as the data it operated on should be stored in the computers”. Von
Neumann first proposed this concept and it is one of the most brilliant ideas in the computer field in
the 20th century.

EDSAC also incorporated the stored program concept and it began operation before EDVAC in
1949. EDSAC is attributed to a team headed by Maurice Wilkes and it is the world’s first stored
program computer.

UNIVAC is the first commercially successful computer and it could handle both characters and
numbers.
The Second Generation: 1960-1964
In the second generation efforts have been put to reduce the cost and size of the machine and
increase the speed and reliability of the computer. To achieve this objective, transistors were used as
the basic electronic elements.

Transistors had the following on their credit side. They:

 Are smaller
 Are more reliable
 Use less electric energy
 Generate little dissipated heat

In addition, the computers with transistors could operate much faster than those with vacuum tubes.

Other achievements of this generation include:

 The concept of multiprogramming that allows several users to share the machine jointly.
 The concept of timesharing that allows sharing a computer in which tens or hundreds of users
access the central computer through dumb terminal.
 The introduction of high-level computer programming Languages (FORTRAN and ALGOL).
The Third generation: 1965-1971
In the third generation the integrated circuit (IC) technology was introduced. Integrated circuits are
electronic components that consist of several hundreds of small transistors on a single silicon chip.
The use of these chips served the purpose of reducing the cost, size and power requirements and
increasing the operating speed and the reliability of the machine substantially.

The most important computers of this generation are the IBM/360 series. The family concept of
computers was introduced by which an organization could start with a small computer system and
then upgrade to larger systems as it grew.

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Other advantages of the third generation computers over the previous ones include:
 Better storage devices
 Improved input/output devices
 Low cost of auxiliary memory or storage devices.

The Fourth Generation: 1972- present

The fourth generation is marked by the use of Large-Scale Integrated circuits (LSI) and very large-
scale integrated circuits (VLSI) with many thousands of transistoGrs on a single silicon chip. This
generation is also called the microcomputer generation as a result of the introduction of the
microprocessor. The microprocessor is a single chip that performed all the operations of the
computer’s processor.
Computer power that might have cost hundreds or thousands of dollars some decades ago now costs
only a few dollars – an incredible achievement.
Other advantages of the fourth generation include:
 More compact size (miniaturized)
 Much faster than ever
 More accurate and reliable
 Better memory and storage capacity
 Better interface between the user and the computer.
The Fifth Generation
Computers of this generation are said to be truly intelligent machines that is, machines that:
 Learn from experience (heuristic devices)
 Incorporate artificial intelligence
 Can process natural Language.
As a matter of fact, these machines are said to incorporate most of the virtues that human beings
have.
Concluding Remarks
As can be seen from the various advancement phases of the computer technology size, cost and
reliability of the machine is directly linked to the technology used to build it.
Another interesting point worth mentioning is that the computer industry has managed to become
one of the three world’s giant industries with the petroleum and the automobile industry. This is
attributed to the rapid development and changes it has gone through.
Each of the first four generations was characterized by a major advance in the hardware
component (electronic) and it is widely believed that a breakthrough in the software make the
fifth generation possible.

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Generation Time Circuit Storage Languages Operating Access Time

elements devices systems
First 1950s Vacuum Punched cards Machine Operator 1 millisecond
tubes &assembly controlled
Second 1960-1964 Discrete Magnetic tape COBOL Batch 10 microseconds
transistors FORTRAN
Third 1965-1971 IC Magnetic disk Structured Interactive 1 nanoseconds
Language
Fourth Late1970s VLSI Mass storage Applications Virtual 100nanoseconds
oriented

2.2 Characteristics of computers

Human being develop computer so that it can perform intricate operation, such as calculation data
processing, or simply for entertainment. Today, much of the world’s infrastructure runs on
computers and it has profoundly changed our lives.
Computer is a machine; just like other machines with the following unique features.
 Programmability: the computer can do virtually anything, provided that it is given the right
set of instructions to do the job. Other machines may do a set of predefined tasks, nothing
more nothing less.

 Storage and Retrieval: Unlike other machines computer can store data for indefinite period
of time and makes the data available for later retrieval.
Other distinguishing features of the computers are:
 High speed: computers process data at extremely fast rate, at millions or billions of
instruction per second. The speed of computer is calculated in MHz (Megahertz) that is
one million instructions per second. At present powerful computers can perform billions
of instruction in just one second.

 High precision and accuracy: computers are very accurate. The level of accuracy
depends on the instruction and the type of machine being used. Since computers are
capable of doing what it is instructed to do, faulty instruction for data processing may
lead to faulty results. This is known as GIGO (Garbage In Garbage Out).

 Diligence: A computer being a machine that doesn’t suffer from the human traits of
tiredness and lack of concentration. If 1 million instructions have to be performed then
the computer will perform the last millionth instruction with same accuracy and speed as
the first instruction.

 Reliability: generally reliability is measurement of performance of a computer, which is

measured against some predetermined standard for operation without any failure. The
major reason behind the reliability of the computer is that, at a hardware level it doesn’t
require any human intervention between its processing operations.

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 High storage capacity: computer can store large amount of data and can recall the
required information almost right away. The main memory of the computer is relatively
small and it can hold only certain amount of information, therefore, the data is stored in
secondary storage device such as magnetic tape or disks. Small section of data can be
accessed very quickly and bought into storage devises, as and when required, for
processing.

 Versatility: computers are quite versatile in nature. Versatility, literally, means “with
many uses”. It can perform multiple tasks simultaneously at equal ease. For example, at
one moment it can be used to draft a letter, another moment it can be used to play music
and in between, one can print a document as well. All this work is possible by changing
the program (computer instruction).

 Resource sharing: in the initial stage of development, computers used to be isolated

machine. With tremendous growth in computer technologies, computer today have the
capability to connect with each other. This has made sharing of costly resources like
printers possible. Apart from device sharing, data and information can be shared among
groups of computers, thus creating a large information and knowledge base.

Although the processing becomes less tedious with the development of computers, it is still time
consuming and expensive job. Computer parts need regular checking and maintenance in order to
give correct result. Further computer need to be installed in a dust free place. Generally some parts
of a computer get heated up due to heavy processing. Therefore, the ambient temperature of the
computer system should be maintained.

2.3 Types of computers

Computers can be categorized broadly based on:
 The type of data they process (method of operation)
 The purposes of application
 Their physical size, speed, storage capacity, and price.
Based on the type of data they process
Computers may process analog data or digital data. Hence computers can be either digital or analog.
Virtually all-modern computers are digital. Digital refers to the processes in computers that
manipulate binary numbers (0s or 1s), which represent switches that are turned on or off by electrical
current. A bit can have the value 0 or the value 1, but nothing in between 0 and 1. Analog refers to
circuits or numerical values that have a continuous range. Both 0 and 1 can be represented by analog
computers, but so can 0.5, 1.5, or a number like p (approximately 3.14).

A desk lamp can serve as an example of the difference between analog and digital. If the lamp has a
simple on/off switch, then the lamp system is digital, because the lamp either produces light at a

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given moment or it does not. If a dimmer replaces the on/off switch, then the lamp is analog, because
the amount of light can vary continuously from on to off and all intensities in between.

Analog computer systems were the first type to be produced. A popular analog computer used in the
20th century was the slide rule. To perform calculations with a slide rule, the user slides a narrow,
gauged wooden strip inside a ruler like holder. Because the sliding is continuous and there is no
mechanism to stop at any exact values, the slide rule is analog. New interest has been shown recently
in analog computers, particularly in areas such as neural networks. These are specialized computer
designs that attempt to mimic neurons of the brain. They can be built to respond to continuous
electrical signals. Most modern computers, however, are digital machines whose components have a
finite number of states for example, the 0 or 1, or on or off bits. These bits can be combined to
denote information such as numbers, letters, graphics, sound, and program instructions.
In summary, analog computers measure things. Digital computers, in contrast, count things. A digital
computer is one that operates on discrete data. Analog computer in contrast is one that operates on
continuous data.

Hybrid computers are both digital and analog. They can serve as both digital and analog. They can
measure continuous flow of data (act as analog) and manipulate discrete values (0s and 1s).
Classification by purpose of application
Computers can be applied or used for different purposes. Based upon their application, they are
classified as special purpose or general purpose computers.
Special purpose computers
They are designed to solve a single type of problem, that is their components and their functions are
uniquely adapted to a specific situation involving specific application.

Example:
 The public telephone box
 Traffic control system
 Ticket machines (used in grocery, super market etc.)
 Pocket-calculators etc.
 Counters
Most analog computers are special purpose computers.
General purpose computers
They are designed to solve variety of problems through the use of “store program concept”. A
program or set of instructions designed to solve a problem is read and stored into the memory and
then executed by the computer one by one. The same computer can be applied to solve another set of
problem using different program. General computers are more flexible and versatile.
Examples
 Micro computers
 Mini computers

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 Mainframe computers
 Super computers etc.

With respect to physical size, speed, storage capacity, and price

Based on their size, speed, storage capacity and price computers can be categorized into four major
groups.
1. Microcomputers
2. Minicomputers
3. Mainframes
4. Super computers (Monsters)
Micro computers
Microcomputer, desktop or notebook size computing is a device that uses a microprocessor as its
central processing unit, or CPU. Microcomputers are also called personal computers (PCS), home
computers, small-business computers, and micros. The smallest, most compact are palm tops.
Laptops are also small in size (size of brief case). When they first appeared, they were considered
single-user devices, and they were capable of handling only four, eight, or 16 bits of information at
one time. More recently the distinction between microcomputers and large, mainframe computers (as
well as the smaller mainframe-type systems called minicomputers) has become blurred, as newer
microcomputer models have increased the speed and data-handling capabilities of their CPUs into
the 32-bit, multi-user range.

Computer circuit board integrated circuits (ICS) make the microcomputer possible; without them,
individual circuits and their components would take up far too much space for a compact computer
design. Also called a chip, the typical IC consists of elements such as resistors, capacitors, and
transistors packed on a single piece of silicon. In smaller, more densely packed ICS, circuit elements
may be only a few atoms in size, which makes it possible to create sophisticated computers the size
of notebooks. A typical computer circuit board features many integrated circuits connected together.

Mini computers
Minicomputers, the first of which entered general business use in the early 1960s, are now
widespread in commerce and government. Terminals linked to the central processing unit (CPU) are
under the direct control of the individual user rather than centralized staff. In recent years, however,
it is the microcomputer, or personal computer (pc), that has come to play the principal role in most
office workplaces

Minicomputer, a mid-level computer built to perform complex computations while dealing

efficiently with a high level of input and output from users connected via terminals. Minicomputers
also frequently connect to other minicomputers on a network and distribute processing among all the
attached machines. Minicomputers are used heavily in transaction-processing applications and as
interfaces between mainframe computer systems and wide area networks.
Mainframe computers

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Mainframe computers have more memory, speed, and capabilities than workstations and are usually
shared by multiple users through a series of interconnected computers. They control businesses and
industrial facilities and are can also be used for scientific research.
Mainframe computers are large, very expensive, high-speed machines that require trained operators
as well as a special temperature-regulated facility to prevent overheating. Use of these machines
today is limited to large organizations with heavy-volume data-processing requirements. Time-
sharing, allowing more than one company to use the same mainframe for a fee—was instituted to
divide the cost of the equipment among several users while ensuring that the equipment is utilized to
the maximum extent.

Mainframes with remote terminals, each with its own monitor, became available in the mid-1970s
and allowed for simultaneous input by many users. With the advent of the minicomputer, however, a
far less expensive alternative became available. The transistor and microelectronics made
manufacture of these smaller, less-complex machines practicable.
Super computers
Supercomputer, computer designed to perform calculations as fast as current technology allows and
used to solve extremely complex problems. Supercomputers are used to design automobiles, aircraft,
and spacecraft; 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 behavior and evolution of stars and galaxies. Supercomputers are also
used extensively by the military for weapons and defense systems research, and for encrypting and
decoding sensitive intelligence information.

Supercomputers are different than other types of computers in that they are designed to work on a
single problem at a time, devoting all their resources to the solution of the problem. Other powerful
computers such as mainframes and workstations are specifically designed so that they can work on
numerous problems, and support numerous users, simultaneously. Because of their high cost usually
in the hundreds of thousands to millions of dollars—supercomputers are shared resources.
Supercomputers are so expensive that usually only large companies, universities, and government
agencies and laboratories can afford them.

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CHAPTER THREE
3. The computer system Organization
As discussed in the earlier parts, a system, generally, is any collection of component elements (also
called subsystems) that work together to perform a task. The components collectively make the
whole (the system). Each component has a specific task to accomplish. A computer is not a single
machine. It is a system and the system contains lot of subcomponents. A computer system is made
up of both hardware and software. Software is another term for computer program. Software
controls the computer and makes it do useful work. Without software a computer is useless.
Hardware refers to the physical components that make up a computer system. These include the
computer's processor, memory, monitor, keyboard, mouse, disk drive, printer, and so on.

3.1 Computer Hardware

Hardware is the general term for the physical devices that carry out the activities of capturing,
processing, storing, and communicating data and information. The hardware of a computer system is made
up of a number of electronic devices connected together. It is composed of a number of interacting physical parts based
on the need of the information flow.

The computer hardware falls into four categories:

 Input devices
 Processors
 Output devices
 Storage devices
3.1.1 Input Devices
An input device is any machine or device that feeds data into a computer.
Input devices are the part of computer hardware that is used to convert data or information into
electronic machine-readable form. These devices enable a computer user to enter data,

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commands, and programs into the CPU. These devices convert information from a form suitable
to human beings to one understandable by the computer.
A cursor, a blinking line on the computer screen, indicates the point at which data or information
will be input. The following are some of the devices that are commonly used to input data to the
computer:
• Keyboard
• Mouse
• Voice recognition devices
• Scanning devices
• Digital computer cameras
• Optical data readers
• Automatic teller machines, etc.

Keyboard:
The QWERTY keyboard, so called because the keys ’Q’,’W’,’E’,’R’,’T’ and ’Y’ are adjacent, is the
commonest form of keyboard. But other types of keyboard are available, some being specially
designed for people with special needs. It should be noted that the layout of keys on the QWERTY
keyboard owes its origins to typewriter designers who were actually trying to slow down the speed at
which a typist could type. The reason was that the old lever-based typewriters were liable to levers
getting interlocked if two keys were pressed in rapid succession. Typewriter designers laid out the
keys in a fashion that made it difficult to type quickly, the QWERTY layout being the product of this
design. Because so many people trained on such keyboards, the layout still remains with us today,
many years after the engineering problem which it was designed to alleviate disappeared. It is worth
noting that in some non-English speaking countries the layout is slightly different giving rise to
QWERTZ and AZERTY keyboard layouts.
A keyboard normally consists of 101/102 or 105 keys. These keys can be divided into five sections.
 Typing keys: These keys work just like a conventional typewriter. These keys include
English alphabets a-z, digits 0-9, the enter key, space, the backspace key, the shift key,
the caps lock key, etc.
 Function keys: These keys perform different tasks based on the type of software being
used. These keys are labeled as f1, f2… and f12.
 Numeric keys: These keys let you enter numerical data more easily when you are
working on number intensive tasks. To use this section of the keyboard make sure that
the Num Lock key is on.
 Navigation keys: These are keys that are used to navigate through your document. The
following are navigation keys.
Page up, page down, home, end,, , , , etc.
 Computer keys: These are keys not found on typewriters. They perform different tasks
when used alone or in conjunction with other keys.
Esc, alt, ctrl, print screen, scroll lock, pause, insert, delete

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The following keys are very important:

 The shift keys are used to type capital characters and special characters labeled on the keys
such as ?, !, @, &, #, @, $, *, etc.
 Alt and ctrl are modifier keys that are used in conjunction with other keys to perform a
function.
 The print screen key is used to print a paper copy of whatever is on the screen when the key
is pressed (if a printer is attached).
 The pause key temporarily suspends an activity. Pressing the pause key once stops the
activity, pressing any typing key (except shift, caps lock) resumes the activity.
The keyboard also has a status-indicator area. This area has three lights that display the status (on or
off) of num lock, caps lock, and scroll lock. When one of these indicator lights is on, the
corresponding mode is on.
Mouse
 Mouse is a hand-operated device that controls the movement of the cursor or pointer on a
display screen. It is a small object that can be rolled along a rough flat surface.
 Its name is derived from its shape, which looks a bit a mouse; it’s connecting wire that one
can imagine to be the mouse’s tail and the fact that one must make it survey, along a surface.
 Mouse can have as many as three buttons whose function depends on what program is
running
 Mouse was invented by Douglas Engelhard of Stanford research center in 1963. It is one of
the great breaks through in computer ergonomics because it fees the user to a large extent
from using the keyboard.
Mouse pad - Is a pad on which you can move a mouse. It provides more traction than smooth
surfaces such as glass & wood, so they make it easier to move a mouse accurately.
Scanners
 Are input devices that can read text or illustrations printed on paper & translate the
information into a form that a computer can use.
 Device which scans an image (document, photograph) and produces a digital version of the
image i.e. the image is stored as a sequence of binary numbers. Special software can then
display the digital version of the image on a monitor. They effectively photocopy the image
into the computer. This type of technology is very useful for storing legal documents,
application forms and anywhere there is a requirement to access the contents of an original
document very quickly.

Fig. Scanner

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Bar code scanners

 A bar code is a computer readable code consisting of bars or lines of varying widths or
lengths
 Bar code system called Universal Product Code is used in supermarkets.

Digital camera and video cameras: - are used to capture a single frame images or continues video
streams for the pc. There are digital and photographic cameras attached to your pc to create image
and video files.

Speech recognition devices

 Often used in multimedia systems
 Capture the voice or sounds for use in computer processing
 Converts a person’s input into digital form

3.1.2 The Central Processing Unit (CPU)

The CPU, also called the processor, as its name suggests, is the unit that does the work of the
computer system i.e. it executes computer programs. A computer programs is composed of
instructions, which are executed (obeyed) by the processor. These instructions tell the processor
when and what to read from a keyboard; what to display on a screen, what to store and retrieve from
a disk drive and so on. A computer program is a set of such instructions that carries out a meaningful
task. It is worth remembering at this stage that the processor can only perform a limited range of
operations, logical and arithmetic. It can compare numbers and perform input/output (read
information and display or store it) or perform one of the arithmetic operations like addition,
subtraction, division or multiplication. It has no magical powers. It is instructive to bear in mind that
all computer programs are constructed from sequences of instructions based primitive operations.
The CPU may be a single chip (microprocessor) or a series of chips that performs arithmetic and
logical operations and controls the operations of the other elements of the system.
The processor consists of three functional sections:
The arithmetic and logic unit (ALU) the registers and the control unit,
The Arithmetic and Logic Unit (ALU): - gives the chip its calculating ability and permits
arithmetical & logical operations. The ALU carries out arithmetic operations like addition and
subtraction and logical operations like and, or, etc
The registers: - in addition to the ALU and cu, the processor has a small number (usually less than
100) of storage locations to store information that is currently being processed. These locations are
called registers. They are temporary storage areas that hold data, keep track of instructions, and hold

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the location & results of these operations. Depending on the processor type, a register may typically
store 8, 16, 32 or 64 bits. The register size of a particular processor allows us to classify the
processor. An n-bit processor is said to have an n-bit word size so a 32-bit processor has a 32-bit
word size. The greater the number of bits the more powerful the processor is, since it will be able to
process a larger unit of information in a single operation.
The CPU consists of different types of registers:
 The Program Counter (PC): contains the address of the instruction currently being
executed or the one to be fetched next. More accurately, it is called instruction pointer.
 The Instruction Register (IR): holds the instruction currently being executed.
 The Memory Address Register (MAR): holds the part of the program instruction that
tells the ALU the address of the data that is to be processed next.
 The Memory Data Register (MDR): holds instruction and data just fetched and
temporarily stores the result of processing before they are written to main memory. They
are also called accumulator.
 Packet Status Register (PSR): contains flags that describe the status of the most recent
operation carried out by the CPU.
 General Purpose Registers (GPR): may perform many functions such as handling
constants and/or accumulating arithmetic results.
The Control Unit (CU): - performs all the control functions of the computer. That is, it times and
regulates the operations of the entire computer system; reads instruction from a designated register
and translates it into an activity; and regulates the amount of CPU time that each operation may
consume.
Arithmetic
Input
&
Control CPU Logic Unit
CP Memory Unit [ALU]
interconnection
U

Output
Registers

Fig. Computer inside the CPU

Purposes of CPU
 Fetch instruction: the CPU read instruction from the memory
 Interpret instruction: the instruction must be decoded to determine what action is required
 Fetch data: the execution of an instruction may require reading of data from memory or
an I/O module.
 Process data: the execution of an instruction may require performing some arithmetic or
logical operation on data.
 Write data: the result of an execution may require writing data to memory or an I/O
module.
3.1.3 Memory and storage devices

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Memory also known as primary storage, main memory or internal memory is physically located
close to the CPU (to decrease access time). The CPU interacts closely with memory - referring to it
both for instructions and data and information. However memory is separate from the CPU.
Memory provides the CPU with a working storage area for program instructions and data. The chief
feature of memory is that it rapidly provides the data and instructions to the CPU.

Memory space is used in five different ways.

 To hold the computers operating system program (dos, windows, etc.) That oversees
processing and acts as an interface between the hardware and the application programs.
 To hold applications programs - word processing, spreadsheet, etc.
 To hold data and information temporarily, receiving from input devices and sending them to
output devices during processing.
 To store other data or information needed in processing in the working storage area.
 To provide additional space for programs or data, as needed.
Memory size (storage capacity)
• Like the CPU, memory devices contain thousands of circuits imprinted on a silicon chip. By
representing data as a combination of on or off circuit states, the data is stored in memory.
• Computers vary widely in the amount of internal (primary) memory they have. The size of memory
is measured by the number of storage locations it contains. Each storage location or byte has a
predetermined capacity
• a byte is the amount of memory required to store one digit, letter or character. A byte is equal to
eight bits. Bytes are generally measured by
 Kilobyte (KB, K-Byte)
Although accepted as approximately one thousand, actually means 2 10 or 1,024. A storage device
with 640 kb capacity can hold 640 x 1,024 (or 655,360) bytes.
 Megabyte (MB, M-Byte) :-millions of bytes.
Accepted as approximately one million, actually equals 1,048,576 (1,024 x1,024 or 220)
 Gigabytes (GB,G-Bytes) :-billions of bytes
Accepted as approximately one billion, actually equals 1,073,741,824 (1,024 x 1,024 x 1,024,
or 230)
 Terabyte (TB, T-Byte) :-trillions of bytes
Accepted as approximately one trillion, actually equals 1,099,511,627,776 (1,024 x 1,024 x 1,024 x
1,024 or 240).
RAM (Random Access Memory)
 Random access means that data and information can be written to or read from the any
memory address at any time and randomly.
 In main memory, bytes are identified by a memory address that allows the computer to
determine where an element of data or information is stored.
 Stores data and instructions temporarily
 It is volatile in that its contents exist as long as electric current is maintained.
 Ram chips lose their contents if electric current is turned off or disrupted.

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 Ram chips are directly mounted on the computer’s main circuit board on chips mounted on
peripheral cards that plugs into the computer’s main circuit board.
 Ram chips consist of millions of switches that are sensitive to changes in electric current.

ROM (Read Only Memory)

 Provides random access to a memory location
 Holds data and information even after the electrical current is turned off—it is non volatile.
 Unlike the contents of ram chips, the contents of ROM chips cannot be changed—it provides
permanent storage.
Secondary storage devices
The term storage or secondary storage refers to the parts of a computer that retain data permanently,
even after turning off the computer. Examples of storage devices would be floppy disk, hard disk,
compact disk (CD), digital versatile disk (DVD), and magnetic tape. Commonly used secondary
storage devices can be grouped as magnetic or optical. Magnetic devices use magnetic technology to
write and read data from the storage surface. This category includes hard disk, floppy disk, and
magnetic tape. On the other hand, optical storage devices use laser technology. CD and DVD fall
under this second category.
a) Magnetic storage devices
Floppy disk
A storage medium that is made from a disk of flexible plastic (the "floppy" part) covered with a
magnetic material. The floppy disk is many decades old. The standard floppy disk can hold 1.44mb
of data and has 3.5 inch diameter. Floppy disks are slow, unreliable and can hold much less data than
the other storage devices.
Hard disk
A hard disk contains both the disk and the drive (the slot) that is used to read and write data on the
disk. A hard disk uses rigid turning disks to store data and programs. They have read/write heads
which can read data from the hard disk and write data to the hard disk. The hard disk drive is sealed.
This protects the hard disk drive internals from dust, condensation, and other sources of
contamination. Hard disks can store much more data than floppy disks, and access and transmit it
faster. Currently an average hard disk can store 60 to 80 gb of data. For both hard disks and floppy
disks, data is stored on the surface in sectors and tracks.
Magnetic tape
A tape drive, also known as a streamer, is a device that reads data from and writes data to a magnetic
tape. It is typically used for archiving or backing up of data stored on hard disks. Magnetic tapes are
long lasting and inexpensive storage media.
b) Optical storage devices
Optical storage is a newer storage technology using a high-power laser beam to burn small holes in a
disk's surface coating. Data is represented by the presence and absence of holes in the disk’s surface.

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Optical media are more durable than tape and less vulnerable to environmental conditions. On the
other hand, they tend to be slower than typical hard disks, and hold less data.
Compact disk (CD)
A compact disc (CD) is an optical disk used to store digital data.
It was originally developed for storing digital audio.
Types of CDs
The different types of CDs include: CD-ROM, CD-R, and CD-RW:
CD-ROM (Compact Disc – Read Only Memory): is a version of the CD that allows the information
to be stored so that the user can only read from the disks. Once data is recorded on a CD-ROM, new
data cannot be stored and the disc cannot be erased.
Although CD-ROMs look like music discs, they can only be used with a computer equipped with a
CD-ROM drive.
CD-R (compact disc - recordable): refers to compact disks that can be recorded only once, but read
many times. If the recorded content is no longer wanted, additional material can be recorded only on
the remaining space on the disk. The disks themselves are constructed differently from ordinary
CDs.
CD-RW (compact disc - rewritable): is an extension of CD-R whereby you can rewrite data or audio
to the same CD many times. Not all CD drives can read CD-RWs.
Digital Versatile Disc (DVD)
DVD is an optical disc storage media that can be used for storing data, including movies with high
video and sound quality. DVDs resemble CD: their physical dimensions are the same – 12 cm or the
mini 8cm - but they are encoded in a different format. This enables DVDs to store more data than
that of CDs. A typical DVD can often hold more data than 6 CDs. DVDs can store an entire movie,
or several hours of audio.
Common types of DVDs
 DVD-ROM: these DVDs are read-only disks. They are accessed using a special DVD drive
attached to a personal computer. They are often used for movies (which are more
specifically referred to as DVD-video) and computer games.
 DVD-R: it offers a write-once, read-many time’s storage format similar to CD-R, but can
hold more information than a CD-R.
 DVD-RW: a recordable DVD format similar to CD-RW.
3.1.4 Output Devices
An output device is a peripheral device that enables a computer to communicate (send out)
information to the user. It receives information from a computer ram and transforms it into human
readable form (that the user can understand). Output devices are parts of the computer that are
designed to receive output from the computer and provide it to the user. Examples of output devices
are monitors, speakers, and printers. In general, there are three types of output from a computer. These are:
 Printed or hard copy output
 Display output
 Voice output

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Monitor
A monitor is an output device similar to a television screen that receives video signals from the
computer and displays the information for the user. It is the most commonly used output device for
displaying text and graphics from a computer.
Today's monitors have much better quality displays than any TV. There are two main types of
monitors:
 CRTS (Cathode Ray Tubes): have a large part at the back and are most common on desktop
computers.
 LCDS (Liquid Crystal Displays): are flat screens and are commonly used on laptops and
some desktop systems.
Monitors differ in several ways. However, the major differences are the resolution and the number of
colors it can produce at those resolutions.
Resolution refers to how clear the image on the monitor is. It is a width times height measurement
of computer monitor display capabilities in pixels. Pixels are individual dots that are used to display
an image on a computer monitor. The more pixels a screen can show, the higher the quality.
Resolution refers to how clear the image on the monitor is. It is measured in pixels, which are
individual dots that are used to display an image on a computer monitor.
The more pixels a screen can show, the higher the quality.
Printer
A printer is a device that produces a paper copy, sometimes called a hard copy, of data stored in a
computer. Broadly speaking, there are two types of printers: impact printers and non-impact printers.
Impact printer
With this type of printer, a pin or a hammer strikes the paper and the ribbon together to form a
character, like a typewriter. Impact printers are less expensive but they are noisy and have low print
quality.
Non-impact printers
This type of printer does not involve actually striking the paper. Instead, it uses ink spray or toner
powder. It has low noise and can print graphics and often a wider variety of fonts than impact
printers. However they are more expensive. There are three types of non-impact printers, ink jet,
thermal and laser printers:
Ink jet printer: sprays ink onto paper to form characters and graphics. Most color printers are ink
jet.
Thermal printer: uses heat on chemically treated paper to form characters. Fax machines that use
rolls of paper are of this type.
Laser printer: works like a copy machine, using toner and a heat bar. It is faster and more
expensive than the other printers.
Plotters
Are devices that produce hard copy graphical output for engineering design, whether map, etc.

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Plotter
Speaker
A speaker is an output device that allows you to hear voice, music, and other sounds from your
computer. There are usually two of them and they come in various sizes.

3.2 Computer Software

Software is a term for computer programs. A program is a set of
instructions that enables a computer to operate or instructions that tell the computer how to perform
a specific task.
Computer software has two major categories:
 System software
 Application software
3.2.1 Systems Software
Systems software includes the computer's basic operating system and Language software. The term
also usually covers any software used to manage the computer and the network. Thus we can say
that systems software includes operating systems, device drivers, programming tools, utilities and
more.
Operating systems
An operating system is the most important program that runs on a computer. Every general-purpose
computer must have an operating system to run other programs. Operating systems perform basic
tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping
track of files and directories on the disk, and controlling peripheral devices such as disk drives and
printers.
For large systems, the operating system has even greater responsibilities and powers. It is like a
traffic policeman - it makes sure those different programs and users running at the same time do not
interfere with each other. The operating system is also responsible for security, ensuring that
unauthorized users do not access the system.
As of 2005, the major operating systems in widespread use have consolidated into two main
families: the Unix-like family and the Microsoft windows family.
The Unix-like family is commonly used to refer to many operating systems, which resemble an
operating system called UNIX. The Microsoft windows family contains operating systems such as
windows 9x, windows 2000, and windows xp.
Operating systems provide a software platform on top of which other application programs can run.
The application programs must be written to run on top of a particular operating system. Your choice
of an operating system, therefore, determines the applications you can use.
Language software

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 Are software which is used by programmers to develop application software and translate
programs to machine code.
 Language software is a generic name consisting of various programs that serve as editors &
translators to develop programs in a number of programming Languages.
 Includes: - translators, general purpose routines and utilities & high level Languages
1) Translator: - is a program that converts one or more Languages to another
Language. Three types of translators are assemblers, compilers & interpreters.
a. Assemblers:-is a program that translates assembly Languages into machine code.
b. Compiler: -is a program that translates a high level Language into machine code.
(PASCAL, FORTRAN,COBOL)
c. Interpreter: -is a program that translates each instruction of high-level Language
& executes the instruction before translating the next instruction.
2) The general-purpose routine and utilities include programs, which are used to handle file
processing, editing and debugging.
3) High-level Language software is software, which have their own compilers to detect
syntax errors of the user’s program code.
Example: COBOL, FORTRAN, PASCAL, C/C++ etc.
3.2.2 Applications Software
Applications software allows a user to accomplish one or more specific tasks. Typical applications
software includes office suites, business software, educational software, databases and computer
games. The uses of computers discussed in section 4 of unit1use applications software. The
following are examples of application software:
 Word processing: WordPerfect, open office, AmiPro, and ms-word.
 Desktop publishing: MS-Publisher, quark press, and adobe in design.
 Spreadsheet: lotus 1-2-3, ms-excel, and Corel Quattro pro.
 Database management: ms-access, my sql, and oracle.
 Presentation: ms-PowerPoint, freelance graphics, and adobe persuasion.

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CHAPTER FOUR
4. Data Representation and Computer Arithmetic’s
4.1 Units of Data Measurement and Representation

This section discusses how data is represented in the computer system. It also deals with
measuring units of the size of memory and storage devices.

Digital computers store data using two state components. With two such states, we can
represent exactly two different values. These two values correspond to the two digits used
by the binary number system. As such, the computer employs the binary number system.
The binary number system works just like the decimal number system, with two
exceptions: the binary number system allows only the values 0 and 1 (rather than 0- 9),
and the binary number system uses powers of two rather than powers of ten.
Units on data measurement
Bits, bytes, kb, mb
A bit (short for binary digit) is the smallest unit of data; it represents one binary digit (0
or 1). However, computers usually do not operate on single bits; rather they store and
manipulate a fixed number of bits. Most often, the smallest unit or number of bits a
computer works with is eight bits. These eight bits make up a byte. A byte is a group of
eight bits that usually make up a single character - letter, number, or special character.
Most coding standards use eight bits, and the eight bits represent a single character, such
as the letter “a” or the number “7”. Thus, the computer can store and manipulate an
individual byte (a single character) or a group of bytes (several characters, a word) at a
time. These individual bytes, or groups of bytes, form the basic unit of memory. The
memory size can be measured in kilobytes (kb), megabytes (mb), gigabytes (gb), etc. The
common units are shown in the following table:

Unit Equivalent Quantity

1 byte 8 bits =1 character

1 kilobyte (kb) 210 =1,024 bytes

1 megabyte (mb) 220 = 1,048,576 bytes

1 gigabyte (gb ) 230 = 1,073,741,824 bytes

1 terabyte (tb) 240 =1,099,511,627,776 bytes

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Units of Data Representation

 When data is stored, processed or communicated within the computer system, it is

packed in units;
 Arranged from the smallest to the largest, the units are called bit, byte and word;
 These units are based on the binary number system;

Bit

 Bits are the smallest units and can convey only two possible states 0 or 1;
 Bit stands for binary digits;
 A bit is a single element in the computer, on a disk that stands for either “on”
indicating 1 or “off” indicating 0;
 In the computer “on” is represented by the existence of current and “off” is
represented by the non existence of current
 On a magnetic disk, the same information is stored by changing the polarity or
magnetized particles on the disk’s surface;

Byte

 Bits can be organized into large units to make them represent more and meaningful
information;
 This large unit is called a byte and is the basic “unit of data representation” in a
computer system;
 The commonly used byte contains 8 bits;
 Since each bit has two states and there are 8 bits in a byte, the total amount of data
that can be represented is 28 or 256 possible combinations;
 Each byte can represent a character(a character is either a letter, a number or a special
symbol such as +,-,?,*, $, etc
 A byte is then used as a unit of measurement in the computer memory, processing
unit, external storage and during communication;
 If the computer memory is 524288 byte, this is expressed in short by saying 512kb,
where kb stands for kilobyte.
 1 Kilobyte(1KB) is 210 or 1024 bytes
 1 Megabyte(MB) is 220 bytes or 210 kilobytes
 1 Gigabyte(GB) is 230 bytes or 220 kilobytes or 210 megabytes

Word
 Word refers the number of bits that a computer process at a time or a
transmission media transmits at a time

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 Although bytes can store or transmit information, the process can even be faster if
more than one byte is processed at a once;
 A combination of bytes, then form a “word”
 A word can contain one, two, three or four bytes based on the capacity of the
computer;
 Word length is usually given in bits
 We say that a computer is an 8-bits, a 16 bit, a 32 bit or a 64 bit computer to
indicate that the amount of data it can process at a time;
 The large the word length a computer has the more powerful and faster it is.
4.2 Computer Arithmetic
Number Systems
There are different number systems. Some of are:
 Decimal number systems
 Binary number systems
 Octal number systems
 Hexadecimal number systems

Decimal Number Systems (base 10)

 It is the common and widely used number system
 It uses 10 symbols to represent or count things
 Probably it was invented because we have 10 fingers with which we count and
add.
 For numbers greater than 9 it uses the symbols 0-9 to represent the number
example 10 which is a combination of 1 and 0 and so on.
Binary Number System (base 2)
 What if we had only two fingers we might use 0, and 1 and for numbers greater than
1 we might use 10 and so on.
 It uses 2 symbols 0, and 1 for rest it represents them in terms of 0 and 1 example 2 as
10 and so on.
Example
0
1
10
11
100
101
110
111 etc

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Octal Number System (base 8) (Oct)

 Again what would happened if we had only 8 fingers off course we would have
used the 8 symbols (0-7) and for numbers greater than we would represented them
in terms of the first 8 symbols example for 8,10 and so on.
 It uses 8 symbols 0-7 to represent numbers

Ex. 0
1
2
3
4
5
6
7

When we compare the octal with the decimal 0-7 in octal is the same as 0-7 in decimal
but 10 in octal is not the same as 10 in decimal because 10 in octal holds the position of
8 in decimal, off course 10 in octal is the same as 8 in decimal.
Hexadecimal Number System (base 16) (hex)
 Suppose we had 16 fingers instead of 10 in case of 10 fingers they invented
new symbols until they exhausted all their fingers. Now they would have to
invent new symbols because there would have be some more fingers left
 Unrepresented. These extra symbols are usually represented by the letters
at the beginning of the English alphabet.
 It uses 16 symbols to represent numbers. But for the numbers greater than
15 they represented in terms of the 16 symbols example 16 as 10 and so on.
 When we compare the hexadecimal with decimal 0-9 in hexadecimal is the
same as 0-9 in decimal but 10 in hexadecimal is not the same as 10 in
decimal, off course 10 in hexadecimal is equal to 16 in decimal because it
holds the position of 16 in decimal.
Example
0 A
1 B
2 C
3 D
4 E
5 F
6
7
8
9

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Conversion from one base to another

The values that members have within given number systems are largely determined by
their positional notation. Positional notation means that the position of one symbol
relative to other symbols in a given number system determines the value of that symbol.
For example, these symbols 1 & 7 can represent either 1 or 7 or 71 depending upon their
relative position to one another.
The decimal number 135 may be expanded as:
(135) 10 = 1*102+3*101+5*100
 The subscript 10 is used to indicate that 135 is a base 10 number.
 The number 10 in binary is not the same as 10 in decimal because the value of 1 in the
binary is not the same as the value of the 1 in the decimal.
 The binary number 1101 may be expanded as

(1101)2 = 1*23+1*22+0*21+1*20
= (1*8)+(1*4)+(0*2)+(1*1)
= 8+4+0+1
= (13)10

*a number x1 x2 x3 …xn is base m can be expanded as

(x0 x1 x2 x3 …xn)m=x1*mn-1+x2*mn-2+x3*mn-3+ …xi*mn-i+xn*m0

Conversion from decimal (base 10) to other base (base m)

(base 10……….base m)
To convert a decimal number x to a number in base m, divide x by m, find the remainder,
again divide the result by m, find the remainder, continue until the result is 0. And
concatenate (collect) the remainders starting from the last up to the first.

Ex.1 convert (56)10 to base (binary) x=56 m=2

(56)10 =(111000)2
Ex.2 convert (78)10 to base 8 (octal)

(78)10=(116)8
Ex. 3. Convert (30)10 to base 16 (hexadecimal)

(30)10=(1e)16

Convert (16)10 to base 16 (hexadecimal)

(16)10= (a)16
Conversion from base m to base 10 (decimal)

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To convert a number x consists of digits x1 x2 x3 …xn in base m to decimal, simply

expand the number with base m. That is

(x1x2x3…xn)m =x1*mn-1+x2*mn-2 +x3*mn-3+ …. + xi*mn-i+… xn-1*m1+xn*m0

=(y)10

Example 1. Convert (1001001)2 to decimal

=73
2. Convert (234)8 to decimal
=156
3. Convert (101)8 to decimal
=65
4. Convert (a1b)16 to decimal
= 2587
5. Covert (101)16 to decimal
=257
Conversion from binary (base2) to octal (base 8) or hexadecimal (base16) and vice
versa
To convert a number in binary to octal group three binary digits together starting from
the last digit (right and if there are no enough digits add zeros in front (left) and find the
corresponding octal of each group.

Example. Convert 1001001 to octal

1001001=001,001,001
= (111)8

Convert 101101001 to octal

101101001=101,101,001
=(551)8
To convert binary to hexadecimal group four binary digits together starting from right
and if there are no enough digits add zeros at the left.

Ex. Convert 111100100 to hexadecimal

111100100=0001,1110,0100
= 1 14 4
= (1e4)16
To convert from octal to binary, convert each octal digit to its equivalent 3 bit binary
starting from right.

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Ex. Convert (675)8 to binary

(675)8 =110 111 101

=(110111101)2
Convert (231)8 to binary
(231)8 = 010 011 001
=(10011001)2

To convert from hexadecimal to binary convert each hex. Digit to its equivalent 4-bit
binary starting from right.
Ex. Convert (234)16 to binary
(234)16 =0010 0011 0100
= (1000110100)2
convert 2ac to binary
(2ac)16 =0010 1010 1100
=(1010101100)2
Conversion from octal to hexadecimal and vice versa
To convert from octal to hexadecimal, first we have to convert to binary and the binary to
hexadecimal. To convert from hexadecimal to octal, first we have to convert to binary
and then the binary to octal.
Ex.1. Convert (235)8 to hexadecimal
(235)8=010 011 101
=0000 1001 1101
= 0 9 13
=(9d)16
Convert 1a to octal
(1a)16=0001 1010
=000 011 010
=0 3 2
=(32)8

Summary of conversion from one base to another base

From base To base Method

2 10 Expand binary number in powers of 2
10 2 Factor the decimal number by 2
2 8 Group 3 binary digits together
8 2 Each octal digit is converted to 3 binary digits
2 16 Group 4 binary digits together
16 2 Each hexadecimal digit is converted to 4 binary digits

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8 10 Go from 8…….2…….10
10 8 Go from 10 … ..2……..8
16 10 Go from 16 …….2…….10
10 16 Go from 10 …….2…….16
8 16 Go from 8 …….2…….16
16 8 Go from 16 …….2…….8

CHAPTER FIVE
5. Data Communication and Computer Networking
5.1 Data Communication

The need of information has increased from time to time. This leads to the need of
sharing of information among different agents (individual). This may be at different
places or locations data communication is the exchange of information between two

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agents. For exchange of information the information should be transmitted from one
point to another through a transmission media called channel. The following figure
shows the different components of data communication.

Input Transmi Output

Agent device tter Transmiss Receiver device
agent
ion
medium

1 2 3 4 5 6

Source system destination system

Information is transmitted in a form of packets the information is divided into packets

and one packet is transmitted at a time. When a packet of information is transmitted the
sender must be sure that the receiver receives the information and the receiver must check
that it receives correct information. The information is transmitted successfully the
receiver must send an acknowledgment to the sender.
Elements of Communication
 Sender
 Receiver
 Transmission media
Communication=source + transmitter + transmission system + receiver + destination

Mode of transmission
The transmission medium may be physical (it connects the transmitter and receivers
through wire) or logical (there are different mode of transmission)

Simplex transmission: - in this transmission signals are transmitted in only one

direction: one station is transmitter and the other is receiver
Half-duplex transmission:- in this transmission signals are transmitted in both direction,
both stations may transmit, but only one at a time.
Full-duplex transmission: - in this transmission signals transmitted in both direction,
both stations may transmit simultaneously. The medium carries signals in both directions
at the same time.
Transmission media
Transmission medium is the physical path between transmitter and receiver in a data
communication system. The characteristics and quality of data transmission are
determined both by the characteristics of the medium and characteristics of the signal.
Media of data transmission:
1) Guided transmission media- data transmission is through solid medium (wired

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system).
2) Unguided transmission media– data transmission through air /space (i.e
wireless system)
Commonly used guided media:
 Twisted pair

 Coaxial cable

 Optical fiber
5.2 Computer Networks
When a computer system is processing data all by itself, without any interaction or
interconnection with any other computer system, it is called a stand-alone computer
system. A network system is a system of two or more computers that are connected to
each other for the purpose of data communication and sharing of resources.
A network also consists of communication channels that are responsible for connecting
devices with each other and transmitting information..
Some of the most important advantages of a computer network system are:
 Data sharing between different users of computers with certain amount of
data security and access control.
 Sharing of software application systems.
 Distribution of computing load on computers at distributed locations to
reduce peak load.
 Sharing or high power computing resources situated at a central location
on a need basis.
 Sharing of costly special devices by several computer users.
5.2.1 Types of networks
Networks may be classified based on a number of parameters:
 Span of control
 Geographical span

1) According to span of control

Based on span of control computer networks can be classified into two major groups:
 Centralized network
 Distributed network

I) Centralized network
Centralized network has one main CPU that processes all information requests and
handles communication. The main CPU in a centralized network is usually a mainframe

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or minicomputer capable of handling the processing workload of many people

simultaneously. People interface with the host computer by using terminals and other
input and output devices.
A terminal is a hardware device consisting of a keyboard and monitor. There are two
types of terminals:
 Dumb terminals
 Intelligent terminals
Terminals that have no storage or processing capabilities are called dumb terminals.
Because dumb terminals do not have any processing capabilities, they must be connected
to a host computer that can perform any processing functions necessary.
Intelligent terminals, on the other hand, do have limited storage and processing
capabilities.
II) Distributed Network
Distributed network is a collection of workstations connected to each other, along with
various shared storage and input and output devices (for example, scanners and printers).
In a distributed network each workstation can handle some, if not all, of its own
processing. Workstations in a distributed network also maintain local information and
software.
Distributed network can be either
 Client/server, or
 Peer-to-peer
A client/server network is a distributed network in which many workstations (called
clients) are connected to a central host computer (called the server). The clients are the
workstations in a client/server network that maintain local software and information and
do as much of the processing as possible.

A peer-to-peer network is a distributed network in

Peer-to-peer
In a peer-to-peer network, workstations are connected to each other and do not rely on a
server for global software and data, data processing tasks, or communication within the
network. Basically, a peer-to-peer network consists of many workstations connected
together that can share resources and communicate with each other. Each workstation can
be a client at one time and a server at another time.

Peer to peer

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2. According to geographic span:

Based on the geographic span of coverage, computer networks are broadly classified into
three major categories.
 Local area network
 Metropolitan network
 Wide area network
I) Local Area Network (LAN)
 May be located within a single building or campus
Ii) Metropolitan Area Network (man)
 A larger version of a LAN
 May span several corporate offices or an entire city
Iii) Wide Area Network (WAN)
 May span a country, a continent or the entire globe

MAN
LAN LAN LAN

WAN

5.2.2 Network Topology

The way in which connections are made is called the topology of the network. Network
topology specifically refers to the physical layout of the network, especially the locations

Network Topologies
The term topology, or more specifically, network topology, refers to the arrangement or
physical layout of computers, cables, and other components on the network. "Topology"
is the standard term that most network professionals use when they refer to the network's
basic design. In addition to the term "topology," you will find several other terms that are
used to define a network's design:
 Physical layout
 Design

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 Diagram
 Map
A network's topology affects its capabilities. The choice of one topology over another
will have an impact on the:
 Type of equipment that the network needs
 Capabilities of the network
 Growth of the network
 Way the network is managed
Developing a sense of how to use the different topologies is a key to understanding the
capabilities of the different types of networks.

Before computers can share resources or perform other communication tasks they must
be connected. Most networks use cable to connect one computer to another. However, it
is not as simple as just plugging a computer into a cable connecting to other computers.
Different types of cable—combined with different network cards, network operating
systems, and other components—require different types of arrangements. To work well, a
network topology takes planning. For example, a particular topology can determine not
only the type of cable used but also how the cabling runs through floors, ceilings, and
walls. Topology can also determine how computers communicate on the network.
Different topologies require different communication methods, and these methods have a
great influence on the network.
There are four basic types of computer topology: bus, star, ring and mesh.
1. Bus Topology
The bus topology is often referred to as a "linear bus" because the computers
are connected in a straight line. This is the simplest and most common method of
networking computers. Figure 5 shows a typical bus topology. It consists of a single cable
called a trunk (also called a backbone or segment) that connects all of the computers in
the network in a single line.

Figure 5 – the bus topology

Computers on a bus topology network communicate by addressing data to a particular

computer and sending out that data on the cable as electronic signals. To understand how
computers communicate on a bus, you need to be familiar with three concepts:

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 Sending the signal

 Signal bounce
 Terminator
2. The star topology
The star type topology has a controller at its centre that is connected in a star shape to
stations via dedicated transmission lines. The controller at the centre controls all
communications between stations. Accordingly, as and when the central controller fails, the
entire network communication will be disabled.

3. The ring topology

The ring type consists of a network configuration that connects nodes at certain intervals on
a ring-shaped, high-speed data transmission line. All nodes share the ring - the ring is
connected separately to the transmitting and receiving sections of each node. Data placed
on the ring by a station makes its round on the ring.
Each node receives the data and checks to see if the data is addressed to it. When the data
is received by the node to which it is addressed, the node accepts and responds accordingly.
Otherwise, the node reproduces and repeats the data for transmission to the next node.

Token ring access method can be described as follows:

• An idle token rotates around the ring

• A sending computer takes the token and attaches the message to be sent on it

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• The token passes to the neighboring computer and so forth

• The receiving computer takes the token and copies the message and leaves the
token to rotate
• The sender again takes the token and removes the massage from the token to
make the token empty
4. Mesh topology

 Mesh topology has multiple connections between each of the nodes on the network.
 Each computer connects with separate cabling.

mesh Fdfffsdf Mesh Topology

5.3 The Internet

Definition
 The internet is a term used to describe a worldwide network of computer networks
connecting millions of computers around the world.
 The internet is one of the largest, most widely used networks (in fact, a network of
networks) that has evolved and grown overtime. It is a group of two or more networks
that are :

 Interconnected physically
 Capable of communicating and sharing data with each other
 Able to act together as a single network.
 The internet connects millions of computers globally and provides worldwide
communications to businesses, homes, schools, and governments.
Brief history of the internet
The internet has had a relatively brief, but explosive history so far. It grew out of an
experiment begun in the 1960's by the u.s. department of defense. Its goal was to create a
method for widely separated computers to transfer data efficiently even in the event of a

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nuclear attack. If part of the network were damaged or destroyed, the rest of the system
still had to work. That network was arpanet, which linked u.s. scientific and academic
researchers. It was the forerunner of today's internet.
Today's internet is made up of a loose collection of interconnected commercial and non-
commercial computer networks, including on-line information services to which users
subscribe. Servers are scattered around the world, linked to the internet using modems,
phone lines, and satellite links.
From a handful of computers and users, today the internet has grown to thousands of
regional networks that can connect millions of users. It has grown explosively in the
1990s to thousands of regional networks that can connect millions of users. There are
millions of server computers on the internet, each providing some type of information or
service. The number of users of the internet is harder to measure.
Because the internet is a world-wide distributed collection of computers rather than one
central computer that everyone ties into, there is no central, controlling agency, nor can
there ever be (no one is in charge of the internet). There are organizations, which develop
technical aspects of this network and set standards for creating applications on it, but no
governing body is in control. The internet backbone, through which internet traffic flows,
is owned by private companies. Any computer on the internet that is properly configured
can share information with any other computer found there

Advantages of the Internet

The internet helps in various ways:
To get information
You could get information about people, products, organizations, research data,
electronic versions of the printed media, etc. From the internet. You can get easy access
to a wealth of information and entertainment. As such it is often described as the
prototype for a worldwide information "superhighway".
To provide information
Most of what you WAN to provide could be considered global advertising. The best and
most inexpensive way to let people know who you are, what you are doing/have done,
and how
 Publishing: including full test articles, reports, abstracts, computer programs,
and demonstrations
 Extension: in which some of the delays associated with the printed media,
may be reduced.
 Teaching: the possibilities here include both distance learning and assistance
for students

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 Sharing/exchanging information with the outside world.

 Ability to communicate

The internet gives people the ability to communicate with other connected
computer users through electronic mail and real time typed conversations (bulletin
boards, databases, and discussion groups). Users will be able to use electronic mails
to transmit messages, announcements and document/file attachments to other users
within the intranet or over the internet.
How big is the internet?
It's difficult to judge the size of the internet. People and systems are being added
daily. However, it is estimated that in the United States alone, more than 27.5 million
people are connected to the internet.

There are over 150,000 unique domain names in the us alone.

Some of the largest internet search engines have over 30 million web documents
listed, with an annual growth rate exceeding 28%.

There are more than 65 countries currently connected to the internet.

Internet connectivity
You can connect to the internet in one of two basic ways, dialing into an internet service
provider’s (ISP) computer, or with a direct connection to an internet service provider.
The difference is mainly in the speed and cost. In most cases, you connect to your ISP
using a telephone line modem. This type of connection is called the dial-up connection.
Sometimes you go in for a direct connection.
Dial-up connection
To establish a conventional dial-up connection to the internet, you will need the
following
 An account with an ISP ((a company that provides the internet access)
 A telephone connection
 A computer
 Modem (external/internal)
 A communication software
Your internet service provider (ISP) will install the following in your computer:
 Telecommunications software
 A World Wide Web browser.
 An email program.
 An ftp program (optional)
 A newsgroup reader
With all this software installed, you will be ready to access the internet. Your computer
will dial a local number, which is provided by your ISP. Once you have logged into your
ISP, you are connected to the internet.

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There are two classes of computers on the internet, hosts and clients. Unless you have a
permanent link to the internet and your machine is always connected and on-line, then
you are probably a client and not a host.
6.7.4.2. Direct connection
You can also get a direct connection to your ISP, where you have a fixed cable or a
dedicated phone line to the ISP. Often the dedicated line is an isdn (integrated services
digital network) line that is a higher speed version of the standard phone line.
APPLICATIONS and services on the internet
The internet is actually very boring since it is nothing more than hardware connections. It
is the internet applications and services that make the internet come alive.
Internet applications include
 World wide web (www),
 Electronic mail,
 File transfer
 Telnet
 Discussion groups
 Usenet (news group),
 Internet relay chat,
 Search services
World Wide Web(www)
In simpler terms, the web is an internet-based computer network that allows users on one
computer to access information stored on another through the worldwide network.
The www is an internet service that provides a network of interactive documents and the
software to access them. It is based on documents called web pages that combine text,
pictures, forms, sound, animation and hypertext links called hyperlinks. To navigate he
www, users “surf” from one page to another by pointing and clicking on the hyperlinks in
text or graphics.
E-MAIL
Email is the ability to write a message to someone, using a mail program, and use the
internet as a means of delivering that message. Email is not a free service. The cost of your
email is covered in your service charge to your provider.
E-mail is the most popular application of computer communication system. For the purpose
of our discussion, we shall adopt the simplest definition of e-mail as follows:
Email (electronic mail) refers to a computer-based system allowing two or more people to
communicate through the transmission of character coded or graphic information by
electronic means.
Electronic mail, or e-mail, allows computer users locally and worldwide to exchange
messages. Each user of e-mail has a mailbox address to which messages are sent.
Messages sent through e-mail can arrive within a matter of seconds.
a typical electronic mail system requires:

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Personal computer/workstation (through which messages are created, edited, and

displayed);
Communication software (which make electronic mail possible);
Telephone line (which links the sending and receiving computers);
Modem (to provide the communications link), and
Account: e-mail address and password (mail box address and mail box ownership)
Just as a letter makes stops at different postal stations along its way, e-mail passes from
one computer, known as a mail server, to another as it travels over the internet. Once it
arrives at the destination mail server, it is stored in an electronic mailbox until the
recipient retrieves it. This whole process can take seconds, allowing you to quickly
communicate with people around the world at any time of the day or night.
To send e-mail, you need a connection to the internet and access to a mail server that
forwards your mail. The standard protocol used for sending internet e-mail is called
SMTP, short for simple mail transfer protocol. It works in conjunction with pop
servers. Pop stands for post office protocol.
When you send an e-mail message, your computer routes it to an SMTP server. The
server looks at the e-mail address (similar to the address on an envelope), then forwards it
to the recipient's mail server. Once the message arrives at the destination mail server, it's
stored until the addressee retrieves it. You can send e-mail anywhere in the world to
anyone who has an e-mail address. Remember, almost all internet service providers and
all major online services offer at least one e-mail address with every account. Telnet
Telnet is a program that allows you to log into computers on the internet and use online
databases, library catalogs, chat services, and more. To telnet to a computer, you must
know its address. This can consist of words (locis.loc.gov) or numbers (140.147.254.3).
FTP
Ftp stands for file transfer protocol. This is both a program and the method used to
transfer files between computers. Anonymous ftp is an option that allows users to transfer
files from thousands of host computers on the internet to their personal computer account.
Ftp sites contain books, articles, software, games, images, sounds, multimedia, course
work, data sets, and more.

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