BCA - FCIT - Sem I

13 Programming Programming Languages
Languages NOTES

The Chapter Covers :

 Introduction
 Data, information And Knowledge
 Characteristicsof Information
 Comparison between human language and
 Computer Language
 What is a program?
 What is a Programming language?
 Programming development cycle
 Algorithm
 Program Flowcharts
 Pseudocode
 Programming approaches
 Programming Paradigms
 Typesof Programming Language
 Third Generation Language
 Fourth Generation Language
 Summary
 Exercise

INTRODUCTION

You read books and write articles, stories etc. in that particular language (script) which you
feel comfortable with. Books , novels etc. are developed in a particular language. Likewise,
we work in different application softwares for performing our different jobs. We develop
those applications softwares in a particular language. Programming language is not much
different than that of natural language which human beings speak. This chapter will deliver
you information on programming languages in an elaborate way.

233

Fundamentals of DATA, INFORMATION AND KNOWLEDGE
Computers &
Information Technology Data after processing gets converted into information. Therefore data is the foundation of
information. Information enhances the knowledge, therefore, the information is the basis
NOTES of knowledge. In this way data, information and knowledge are mutually related.
Processing of data and production of information are the preliminary stages of delivering
knowledge to the human being. Knowledge enables a person to carry out his job further
with more efficiency.
That is why man requires data and information regularly.

Figure 13.1 : Relation among Data, Information and knowledge
CHARACTERISTICS OF INFORMATION
Information incorporates the following characteristics :

 meaningfulness
 surprising element
 conformity with previous knowledge
 correction to previous knowledge
 brevity
 accuracy
 timeliness
 action oriented
 Meaningfulness : The relevance of information with requirement should be maintained
otherwise the information would be meaningless. For example, if we want to go to
Paris but we are collecting information about Shanghai, it will solve no purpose to us
and will remain irrelevant.
 Surprising Elements : Information should also cover the knowledge about exceptions
such that if any exception occurs, then we should be able to tackle it efficiently.
For example , in an intelligence bureau, some of its members are spying for other
agencies, then it is necessary to take immediate action to stop them. But if bureau
is unaware of such persons, they may lose many vital information to enemy agency.
 Conformity with Previous knowledge : If the information is changed suddenly and
lacks conformity with previous information then it may misguide us in attaining our
objective.
 Correction of Previous knowledge : The information gathered may have some
deficiency or may have some changes, in comparison to the previous knowledge. But
the new information should either insert some positive changes to the previous
knowledge or nullify the previous deviations. New information may be modified but
it should not be so exceptional that it becomes difficult to believe in.
 Brevity : In any detailed report, information should not incorporate irrelevant data
with it. If a detailed report is given to the decision makers then it will be difficult for
them to emphasis on vital items of desired project.Therefore the information should
234 be brief, so that decision maker can evaluate the projects under considerations and
conclude out the best result.

 Accuracy : Information should be accurate. The rate of accuracy could vary with the Programming Languages
requirement. The estimate of the population of a country may have tolerance level NOTES
of 15% which means that the data is 85% correct still it is accepted. But in the case
of a bank, the statement of an account should be 100% accurate, otherwise it may 235
lose its goodwill among its customers.

 Timeliness : To initiate a work, or to rectify any deviation in any activity a timely
information is required. If a doctor receives the reports of the seriousness of the
diseases after the death of the patient, it would be meaningless. If a manager receives
the report of zero inventory after the production has stopped, it would solve no
purpose. Timeliness should be maintained.

 Action Oriented : Many managers receive the information on time but they find it
deficient in some or other means items. This creates difficulties in planning and
actuating the job. So the information should be sufficient in itself, and helpful in
reaching some purposeful decision.

COMPARISON BETWEEN HUMAN LANGUAGE AND
COMPUTER LANGUAGE

Human language and computer (programming) language have one thing common; they
are language and they have the same concept. Both use syntactic and semantic rules. Both
have been evolved after a long period of time. Human languages like English, Hindi and
Urdu are not the output of one day, one year, one decade or one century. It took centuries
and centuries in bringing out this form of language that we speak today. Even today,
languages are evolving. New words are being added. Likewise, computer languages evolved
after a long journey from binaries to mnenonics and algorithms. Computer languages, like
human languages are based upon alphabet, words, phrases etc. Both are used to commu-
nicate. Human languages are used to communicate people locally or globally. Similarly,
computer languages help in communicating between computer and people as well as
computer and computer locally (Intranet) or globally (Internet). In fact the creation of
computer language is inspired from human language. In both languages grammatical and
syntectic mistakes may lead to wrong message. What seems as only difference is that
human languages are spoken while computer languages are not although this is not a very
strong difference yet.

WHAT IS A PROGRAM?

A program or a computer program is a collection of instructions that describes a task, or
set of tasks to be carried out by a computer. Formally speaking, a program is an expression
of a computational method written in a computer language.

WHAT IS A PROGRAMMING LANGUAGE?

A programming language is an artificial language that can be used to control the behavior
of a computer. Programming languages, like human languages are defined through the use
of syntactic and semantic rules, to determine structure and meaning respectively.
Programming languages are used to facilitate communication about the task of organizing
and manipulating information and to express algorithms precisely. Thousands of different
programming languages have been created and every year new languages emerge.

PROGRAMMING DEVELOPMENT CYCLE

When you start the task of programming for an application or start developing a software,
it has to pass so many phases before it takes the final shape. A program is a set of
commands to be implemented by the computer to complete a given task. It's a multi-step
process which includes the identification and solution of the problem, development of
computer solution for the problem and a sequence of commands to be run on the

Fundamentals of computer. While writing the program, one should keep the data in mind which the
Computers & program will process to generate information. The programming process is a set of activi-
Information Technology ties and they are executed to develop and execute a computer program.
While writing a program the following six activities are included :
NOTES
1. Understanding Program Specification
236 2. Designing a Program Model.
3. Determining Correctness of the Program.
4. Coding the Program.
5. Testing and Debugging the Program.
6. Preparing Documentation of the Program.

Understanding Program Specification

There are two main activities in understanding the specifications of the program. The first
activity is to define the problem. The second one is to analyse the requirements.

Defining the Problem

Before starting the building construction, a builder inspects the blue-print, and tests that
all the permits have been obtained and surveys the foundation of the building. Builder
undertakes different preparations to build a high rise building and a dog house. Whatever
be the project it is implemented carefully and indiciously only after measuring the prepa-
ration.
Before designing the programs module the first anticipation which you have to fulfil is that
you should prepare the statement of the problem that the program will solve. Without
discussing the probable solution the definition determines what, after all, the problem is.
It is a simple statement of one or two pages. It should appear like a problem. Problem
defining comes before requirement analysis which is the more comprehensive analysis of
the problem.
Problem determination should be in the language of the user and the problem should be
described from the user's point of view. It generally should not be described in technical,
computer language.
Without understanding the components of the problem the attempt to solve it might prove
a futile exercise. Since, in this condition the solution may not stand true to the need of
theuser. Therefore it is required to prepare the problem statement in such way that it can
explain even minute points of the problem. It can be done in the best manner when the
problem is written in the clear words. The consequence of better problem determination
is always a speedier, simpler and more accurate solution.

Requirements Analysis

Requirements describe expectations that are expected from the program. These are the
first steps in the direction of solution. This requirement determination activity is also
known as "functional specification". A clear set of requirements is important for many
reasons. Clear requirements help determining that it's not the programmer but the user
who conducts the functionality of the programs. If the requirements are clear, the user
may observe them and agrees with them. Clear requirements help you avoid guessing
regarding the requirements of the users. The clear specification of requirements is the key
to success of the program. While analysing the requirements, answering the following
questions can make the analysis more fruitful.

1. What is given as input ?
2. What is expected as output ?
3. How to reach the solution ?

Let us understand input process and output process with an example. A program, on the Programming Languages
request of an operator of a terminal, has to obtain motor car registration record from a NOTES
file. The operator will provide a vehicle registration number and the program will display
detailed description of its owner. If the program is unable to get a record, an error message 237
will be displayed.

Input : Vehicle Registration Number

Process : Look for it using the registration number and after finding it out, again
retrieve the information about the account of the vehicle and its masters
name.

Output : If retrieval gets successful then allow the detail of the vehicle to be
displayed on the screen, but if you don't succeed in it then show the
absence of the registration of the vehicle and display the appropriate
error message.

Designing a Program Model

Once the problem is determined its algorithms (one more term for processing logic) can
be developed. This is the most creative part of programming. In this phase, for reflecting
the possible options of algorithm it can be developed in a larger view.

Algorithm is a formula, recipe or step by step process, which can be followed to get the
solution to the problem.

To be useful as the basis of program writing, an algorithm :

1. Must reach a right solution at a fixed time.

2. Must be clear, accurate and free from delusions.

3. Must be in a format which proceeds towards pretty implementation in a program-
ming language.

To develop a solution and for preparing the algorithm, the flowchart and pseudocode are
among the important tools.

Flowchart produce a solution scene and graphic representation while pseudocode stands
for writing program logic in common English Language. The logic described by these tools
can be written again by using any of the programming language.

Determining Correctness of the Program

The most tiresome and difficult phase in the development of program or algorithm is to
ensure that the program or algorithm is error-free. The correctness of a program or
algorithm is that it should give correct output and do the expected things. The precision
of a program or algorithm can be testified by using any one of following methods- dry run,
independent inspection, structured walkthrough.

Coding the Program

It is a process to turn our solutions such as algorithm (flowchart/pseudocode) into real
computer program. Here we select a programming language and using the syntax and
symantics of language, we convert our algorithm which is represented in flowchart/
pseudocode into programming code.

Testing and Debugging the Program

After the coding is once over, you will insert the program into the computer. Then the
computer will compile our program into machine code. Compiling means to change the
source code, for example the user program which has been written using the high level
language, into machine code, which is a language understandable by the machine.

Fundamentals of The compilation leads to some special sort of errors which are displayed by the computer
Computers & after the process is over. These errors are to be rectified and the program is compiled
Information Technology again. This process goes on till the program doesn't get completely error-free. After it, we
should test, whether the program is performing every task for which it has been designed.
NOTES Three types of errors syntax, execution and logical are often faced.
Syntax Error :
238 Syntax errors are created when the computer is unable to understand the command insert
by the language compiler programer. When such errors are faced, the computer rejects
the program and releases a error message. These errors are faced during compilation and
are easy to rectify. In so many cases, these errors are caused because of spelling errors,
missing comma etc. and incorrect syntax. For example, if we type PRINTT in place of
printf then it causes syntax error.
Execution Errors :
These errors are faced during the execution of the program after error-free compilation.
The execution error is also called run-time error. The probable reasons of such mistakes
are as follows -

1. Use of infinite loop.
2. Correct output only for some specific data
3. In-correct data or data in incorrect order.
4. Name of an incorrect file.
5. Divide check error - These appear when a number is divided by zero or by the

number which is very close to zero.
Logical Errors :
The reason of logical errors are the mistakes committed by the programmers while coding
the program. A computer can't identify the logical errors. For example, the formula to
calculate the area of a rectangle is :

AREA = LENGTH * BREADTH
Just because vision fault at the time of coding the formula is written like this -

AREA = LENGTH – BREADTH
It is bound to produce an incorrect result, such errors can only be caught by using dry
run. To rectify these errors, we'll have to carefully study the algorithm of the program.
These errors can be found out by running some sample programs whose answers we know
in advance. By designing the program properly most of such errors can be rectified.
Checking the whole program and carefully done dry-run and walk through are such ways
which can help in removing these errors.
Debugging :
Debugging is a process of identifying the main reason behind the error and removing it.
It is quite opposite to testing, which is a preliminary way of finding the errors.

D ocument at i on

Once a program has been once written and debugged it is ready for action, and therefore
it requires a document or written procedure, in which how to run the program, how to
enter the data, what sorts of problems are expected, and how to handle them are an-
swered. In the documentation of a program, flowchart, pseudocode, program list and
algorithm and processes are included in detail. Documentation is necessary for the main-
tenance of a program. Without proper documentation, it would be more difficult to make
amendments in the program afterwards.

It is a wrong notion that algorithm is the last phase of development cycle. In fact, it should Programming Languages
be combined with the entire phase of programming process, specially with design and NOTES
implementation, for it is expected that documentation helps a person in understanding the
logic of the program. Check Your Progress:
1. What are themain charac-
ALGORITHM
teristicsof Information ?
In the last sections, we have seen, there are many phases in the programming develop- 2. What isaprogram ?
ment cycle. Algorithms are step-by-step commands which are used to complete task of 3. For writingaprogram what
your choice. Every command in algorithm is known as step while is programming lan-
guages, it is generally called statement. act i vi t ies should be in-
deed?
Let us see the out-line of algorithm. To describe algorithm you needn't know anything 4. What isBebugging ?
about computers. What you need to have is a broad thinking and knowledge about your
mother tongue. Suppose, you are given two glasses of coloured water-one red and the 239
other green. Now you are being asked to interchange the water of two glasses. It means
the glass with red colour should contain green water and vise-versa. Let us think of the
solution to this problem.

Step 1 : The glass no. 1 has red water.
Step 2 : The glass no. 2 has green water.
Step 3 : Take an empty glass which is the third one.
Step 4 : The red water of glass no. 1 will be poured into empty glass no. 3.
Step 5 : The green water of glass no. 2 will be emptied into already empty glass
no. 1
Step 6 : Now the red water of glass no. 3 will be poured into glass no. 2 (which
is completely empty).

Its not necessary to write the algorithm in english only, you can write in other languages
also. But the practice is, it should be written in English. The algorithm as a solution to the
above problem will be written like this in English :

Step 1 : Take red water in glass no. 1

Step 2 : Take green water in glass no. 2
Step 3 : Take an empty glass no. 3
Step 4 : Pour red water of glass no. 1 into glass no.3 (Glass no. 1 is empty)
Step 5 : Pour green water of glass no. 2 into glass no. 1 (Glass no. 2 is empty now)

Step 6 : Now pour red water of glass into glass no. 2 which is empty

PROGRAM FLOWCHARTS

Program flowchart is a pictorial presentation of the required logic to complete a task which
contains all the steps of a program. It is called flowchart as it charts the flow of the
program. It is a symbolic representation of every input, output and processing steps. Apart
from being the right method of writing the algorithm it is also a part of the documentation
of the program and helps in maintaining, debugging and understanding the programs.
In a flow charting technique, the operations are denoted as an appropriate symbol for
work. In traditional program flowcharting, simple geometrical symbols are used to repre-
sent the beginning and end of a program, process, decision. These flowchart symbol are
linked by arrow marks to display the sequence of operations. In short, flowchart, is a
graphical representation of operations, activities or procedures by using symbols. It is used
in computer system analysis, activity analysis and common program sequence represen-
tation.

Fundamentals of The following things denote the popularly used symbols and their commonly acceptable
Computers & meanings -
Information Technology
Beginning and end symbol marks the beginning and end of
NOTES a complete operation
Process symbol denotes a function or task and the most
240 used symbol in flowchartings.
Document symbol denotes any type of hard copy input and
output (for example report).
Off-page connector symbols is used to indicate something
that the flowchart continues on the next page. Quite often
for reference the page number is kept in figure.

The Input/Output symbol represents the data which are
available for input or resulting form processing (for example
customer database records).

Comment symbols are used when additional explanation or
comment is required. This symbol is generally attached to
the symbol which it explains with dashed line.
The Decision Symbol is a junction where decision making is
required. In a single entry there can be any number of op-
tional solutions, but only one can be selected.
The Connecter Symbol denotes exit or entry from the other
part of the same flowchart. It is used to break the order of
the flowline which will be continued somewhere else. It is a
good idea till a reference page number for the easy location
of the co-ordinators.
Flowline shows the sequence and direction flow of each feet.

PSEUDOCODE

Pseudocode program is the second and optional method. The program logic uses
pseudocode statement in place of symbols for representing logic steps which acts as bridge
between actual programming and simple English. In pseudocode, every step is written by
using English phrases which are also called construct. A pseudocode is the outline of a
program which is written in a form that can be converted into any actual programming
language statements. A pseudocode neither can be compiled nor can be executed, nor
does it have any actual formatting or syntax rule. The advantage of pseudocode is that it
exempts a programmer from the care of the descriptions of all language rules and they
can focus on algorithm. Without knowing which programming language you will use finally
you can write pseudocode. Some practices which are applied while writing pseudocode
are as follows :

1. All the statements in the loop should be intended. Programming Languages
2. All the alphnumeric value should be enriched by single or double quotation NOTES

marks. 241
3. The beginning and end of a pseudocode should be determined with 'Start' and

'End' keyword.
4. The definite keywords in all the statements should be include indicating a certain

task.
For example the pseudocode for the sum of two numbers will be as follows :

Start
Accept N1
Accept N2
SUM= N1 + N2
Display Sum
End
PROGRAMMING APPROACHES
There are various methods to solve a problem. Usually, we make programs with the aim
of solving problems. There are different programming approaches. They are Top-down,
bottom-up and modular programming.
a. Top-Down Design
Every system has a several hierarchy of components. The top level of component
represents the whole system. Top-down design technique starts from top level
component to lower level (bottom) component. In this technique the system is
divided into some major components. Similarly other components are divided
into some sub components.
b. Bottom-Up Design
This technique of designing a solution is just reverse of top-down design tech-
nique. It starts from lower level component to higher one. It first designs the basic
components and from these basic components it designs higher level compo-
nents. Every higher level component uses the lower level component.
c. Modular Approach
This is the best method for designing a complex system. In this technique we will
divide the large system into some smaller modules. If we discuss a module in
terms of programming, then it is a logical group of some sets of instructions, also
called function or procedure. Each module is a separate part of a program. It is
easy to modify the program with modular approach, because changes in one
module doesn’t affects the other module of the program. It is easier find a bug
in this module.

PROGRAMMING PARADIGMS

A programming paradigm is a fundamental style of programming regarding how problems
solutions are to be formulated in a programming language.
A programming paradigm provides (and determines) the view that the programmer has of
the execution of the program. For instance, in object-oriented programming, programmers
can think of a program as a collection of interacting objects, while in functional program-

Fundamentals of ming a program can be thought of as a sequence of stateless function evaluations. When
Computers & programming computers or systems with many processors, process oriented programming
Information Technology allows programmers to think about applications as sets of processes acting upon logically
shared data structures.
NOTES Just as different groups in software engineering advocate different methodologies, different
programming languages advocate different programming paradigms. Some languages are
242 designed to support one particular paradigm (Smalltalk and Java support object-oriented
programming while Haskell and Scheme support functional programming), while other
programming languages support multiple paradigms (such as Common Lisp, Python, Ruby
and Oz).
Many programming paradigms are well-known for what techniques they forbid as for what
they enable. For instance, pure functional programming disallows the use of side-effects;
structured programming disallows the use of goto. Partly for this reason, new paradigms
are often regarded as doctrinaire or overly rigid by those accustomed to earlier styles.
However, this avoidance of certain techniques can make it easier to prove theorems about
a program’s correctness— or simply to understand its behaviour— without limiting the
generality of the programming language.
The relationship between programming paradigms and programming languages can be
complex since a programming language can support multiple paradigms. For example,
C+ + is designed to support elements of procedural programming, object-based program-
ming, object-oriented programming and generic programming. However, designers and
programmers decide how to build a program using those paradigm elements. One can
write a purely procedural program in C+ + , one can write a purely object-oriented
program in C+ + , or one can write a program that contains elements of both paradigms.

Object-Oriented programming

Object-oriented programming (OOP) is a programming paradigm that uses “objects” to
design applications and computer programs. It can use several techniques from previously
established paradigms, including inheritance, modularity, polymorphism, and encapsula-
tion. Though many modern programming languages support OOP. It was not commonly
used in mainstream software application development until the 1990s.
Object-oriented programming’s roots reach all the way back to the 1960s, when the
nascent field of software engineering had begun to discuss the idea of a software crisis.
As hardware and software became increasingly complex, how could software quality be
maintained? Object-oriented programming addresses this problem by strongly emphasiz-
ing modularity in software.
The Simula programming language was the first to introduce the concepts underlying
object-oriented programming (objects, classes, subclasses, virtual methods, coroutines,
garbage collection, and discrete event simulation) as a superset of Algol. Smalltalk was the
first programming language to be called “object-oriented”.
Object-oriented programming may be seen as a collection of cooperating objects, as
opposed to a traditional view in which a program may be seen as a list of instructions to
the computer. In OOP, each object is capable of receiving messages, processing data, and
sending messages to other objects. Each object can be viewed as an independent little
machine with a distinct role or responsibility.
By way of “objectifying” software modules, object-oriented programming is intended to
promote greater flexibility and maintainability in programming, and is widely popular in
large-scale software engineering. By virtue of its strong emphasis on modularity, object
oriented code is intended to be simpler to develop and easier to understand later on,
lending itself to more direct analysis, coding, and understanding of complex situations and
procedures than less modular programming method.

Structured Programming Programming Languages
NOTES
Structured programming emerged in 1970s. Structured programming is a practice of build-
ing programs out of small modules which were easy to read and understand. Each module
had a single entrance and exit, and performed a single task. Structured programming
practices can be used with any programming language. Prior coding techniques resulted
in spaghetti code that was nearly impossible to read, understand and maintain. Software
developers have found that structured programming results in improved efficiency, but
they continue to struggle with the process of building software quickly and correctly.
Reuse is recognized as the best solution to these software development problems. Reusing
code allows programs to be built quickly and correctly.

Functional Programming

Functional programming is a programming paradigm that treats computation as the evalu-
ation of mathematical functions and avoids state and mutable data. It emphasizes the
application of functions, in contrast with the imperative programming style that empha-
sizes changes in state.
Functional languages include APL, Erlang, Haskell, Lisp, ML, Oz and Scheme.
Functional programming languages, especially “purely functional” ones, have largely been
emphasized in academia rather than in commercial software development. However,
notable functional programming languages used in industry and commercial applications
include Erlang (concurrent applications), R (statistics), Mathematica (symbolic math), Haskell,
and domain-specific programming languages like XSLT.

TYPES OF PROGRAMMING LANGUAGE

It is necessary to know, what the basic requirements of any language are, and what are
the aspects of the computer programmers for any language and also what types of diffi-
culties arise with other languages at that time. The programming languages could be
broadly divided into two categories:

1. Low Level Language
2. High Level Language

Fig. 13.2. : Classification of Programming Language 243

Low Level Language
The language, which doesn’t include any translator to convert its code to machine code
is called low level language. It means the low level language codes are not required to be
translated any way. Machine Language and Assembling Language are the examples of low

Fundamentals of level language. But these languages are very tough to program. It is required to have the
Computers & in-depth knowledge of computer hardware structure. It is also very time consuming and
Information Technology error prone. Also we have to write the program separately for each platform. Since the
low level languages are related with computer hardware directly, hence the execution of
NOTES the program is faster than high level languages. Low level language can be classified into
machine level and Assembly languages.

Machine Level Language
The computer system can understand only the digital signals, which is binary 1 or 0.
So the instructions given to the computer can be only in binary codes i.e. 0 and 1.
And the instruction given in the Binary code is called machine language. The machine
language is simple for machines whereas very tough for the programmers. The main-
tenance of machine language program is also difficult. There is possibility for errors
in memory locations of binary instructions. The machine language programs are also
not portable. Every computer system has its own machine codes instruction set, so the
program written on a particular machine will not run on other machine.
Assembly Language
In assembly language the instructions are given in the form of English like words, such
as MOV, ADD, SUB etc. They are called ‘mnemonic codes’. Compared to machine
language, the assembly language is easy to understand. But, as we know that com-
puter is an electronic device and it can only understand the binary codes. So, the
program written in assembly language has to be converted into machine level lan-
guage. The translator which is used for translating the assembly language into machine
language is called “assembler”.
The data are stored into the computer registers and every computer has different set
of registers. So, the program written into assembly language is also not portable. It
means we have to re-translate again for different computer systems.
High Level Language
High level language is designed keeping in mind the features of portability, means these
languages are machine independent. The high level language is English like language code,
so it is easy to code and understand. The high level languages require a language translator
to convert the high level language program into the machine code. The translator which
is used to do so, is called compiler or interpreter. FORTRAN, COBOL, BASIC, PASCAL,
C, C+ + , Java are few high level languages.

Generation Language Period
1st Generation Machine Language 1940- 1950
2nd Generation Assembly Language 1950- 1958
3rd Generation High Level Language 1958- 1985
4th Generation 4GLs 1985 onward

THIRD GENERATION LANGUAGE

Third generation languages were the first that relaxed programmers from writing programs
in machine and assembly languages. In the third generation languages, english words
replaced the binaries and mnemonics that were difficult to understand. Now, program-
ming became understandable to the learners and even learning process got simpler.
The third generation languages were not machine dependent and therefore could be
written without understanding the architecture of machine. Moreover, programs got por-
244 table means you could have copied the coding from one computer to the other with their

compiler or interpreter. Some of the most popular third generation languages included Programming Languages
BASIC (Beginner's All Purpose Symbolic Instruction Code), PASCAL, COBOL, C and C+ + NOTES
and so on are being discussed in brief here.
245
 BASIC – BASIC is contracted form of Beginner's All Purpose Symbolic Instruction

Code. It is widely used in micro computers and very easy to learn. It was developed
by Dr. John Kemeny and Thomas Kurtz jointly at Dart Mouth College, America in
1964. It is an appropriate language for learning computer programming. It is mostly
available on personal micro computers. BASIC uses interpreter to translate instruc-
tions in machine language. After writing each instruction, it is checked by interpreter
which causes instant information regarding any error. Due to these reasons this is
popular amongst programming learners. It takes less space on computer as its trans-
lator is small in size. It can work on most of the micro computers. BASIC is available
in the market in many versions today. GWBASIC and BASIC are the most popular
versions.

 FORTRAN – FORTRAN stands for Formula Translator. John Backus, from Interna-

tional Business Machine, in 1957 had developed it. This is a high level language
meant for solving scientific and mathematical problems.

FORTRAN IV was one of its several most popular versions. Algebraic calculations can
be performed easily with this language. FORTRAN has become Fortran now.

 COBOL – COBOL is an abbreviated form of COmmon Business Oriented Lan-

guage. This is used for solving problems of business data processing. Commander
Grace Murray Hopper and his team had developed it in the department of American
Defence in the year 1959. Later its development work was handed over to a group
named Conference on Data Systems Languages (CODASYL). The first official report
on COBOL was published in 1960. Later in 1968 its new version after some im-
provements appeared. Latter versions came in 1974 and 1984. Presently COBOL is
used as business data processing.

Development of COBOL aimed at promoting such a language which was not ma-
chine dependent and its programs could execute on different computers. COBOL
has got its own compiler to translate its programs into machine language.

 PASCAL – It is derived from ALGOL 60. It was named after the great mathema-

tician Blaise Pascal. Niklaus Wirth had developed it in 1970 for preparing system
softwares. This is a Block Structured Language.

 C – C language was developed in 1972 at AT & T Bell Laboratories in America. It

was developed by Dennis Ritchie. The name was derived from its earlier versions B
and BCPL. Today it is widely used in software developments. Apart from this, it is
related with UNIX which has increased its uses. Several built-in programs of Unix
were written in C language. C language is a powerful language because it provides
the data address in the memory.

 C++ – C+ + Language was developed to overcome troubles of solving repeatedly

the same problem. It is supposed to be an extension of C language. Bjarne Stroustrup
had developed it in 1980 at Bell laboratories. This language was developed based on
a new technique - object oriented programming leaving tradition of procedure ori-
ented language behind. Object oriented programming is such a method which can
develop complex and large programs. These sorts of programs were difficult to
handle so far.

 Java – Java is a language developed by Sun Microsystems in the decade of 1990.

It is specially used in web programming to create applets (small interactive programs)
for web pages. Java language creates self-contained codes for execution. Hence they
may be called platform independent languages.

Fundamentals of FOURTH GENERATION LANGUAGE
Computers & Fourth generation languages are easier to use than the third generation languages. Nor-
Information Technology mally, fourth generation languages use visual environment instead of textual environment
that was used generally in third generation languages. In textual environment, program-
NOTES mers use English words to create source codes. One line statement of fourth generation
languages equals to several lines of statements of third generation languages. In the visual
246 environment of the fourth generation language, programmers use toolbar to drop and
drag items like buttons, labels and text boxes and create visual definition of an applica-
tion. Once program designed the appearance of a program objects can be assigned
objects several responsibilities on the screen.
Most fourth generation languages provide programmers an integrated development en-
vironment to use it for software development. Integrated development environment of-
fers the programmers all necessary tools for applications development in a particular
program. Compilers and run-time supports are also available for their applications. Microsoft
Visual Studio and Sun's Java Studio are two such examples of commercial integrated
development environment. Visual Basic, C+ + , C# , Dreamweaver, JavaScript are a few
examples of this generation language.
The fourth generation language incorporates several features in itself and its pitfalls can
hardly be found out. However, all have some negative aspects with their positive ones.
Some of their advantages and disadvantages are mentioned in a nutshell as follows -
Advantages

 The fourth generation language is easy to learn and software development is
simple here.

 Fourth generation language provides textual interface as well as graphical inter-
face.

 Programmers have alternatives in the fourth generation languages as the number
is quite big.

 Programming takes less space in the fourth generation languages as one line
written in this generation language equals to several lines in the earlier genera-
tion languages.

 Availability of the fourth general language is not difficult.
Disadvantages

 The fourth generation languages require high configuration computers to run.
 Expertise is less required in the fourth generation languages means easy program-

ming enables novices develop softwares. Consequently, importance of experts
diminished.
 In the fourth generation there is a big series of programming languages that
makes it a bit difficult to decide which should be used and which should be left.
Fourth generation languages include Visual Studio, Visual Studio.NET, Sun Studio etc as
being briefly mentioned here-
 Visual Studio –
Visual Studio includes Visual Basic, Visual C+ + and Visual FoxPro that were earlier
used when textual interface came with visual environment. Now everything starts
getting done in an integrated development environment and commands replaced
with menus and icons. In Visual C+ + IDE programming codes and errors can be
seen highlighted.

 Visual Studio.NET – Programming Languages
.NET technology is an outcome of the world wide web. Now applications are devel- NOTES
oped seeing how useful they can be online. Visual Studio .NET comes with C+ + ,
C# , J# and VB.NET in only one package. Though .NET has been devised to develop
online applications primarily they are equally useful for developing offline or say
traditional softwares.

 Sun Studio One –
Sun Studio One is a visual editor for Java where in an visual environment Java
applications and applets can be developed using in-built features also.

SUM M ARY

 A programming language is an artificial language that can be used to control the
behaviour of a computer.

 Human language and computer language both uses syntactic and semantic
rules.

 A program or a computer program is a collection of instructions that describes
a task, or set of tasks to be carried out by a computer.

 Data, after processing, gets converted into information. Therefore, data is the
foundation of information.

 Meaningfulness, brevity, accuracy, timeliness are a few characteristics of
information.

 Low level and high level are two types of languages.

 Low level language includes machine level and Assembly languages.

 Machine language programs are not portable and difficult to learn.

 Assembly language enables users to write English words like MOV, ADD, SUB
etc. in the programs. They are called mnemonic codes.

 High level language is designed keeping in mind the features of portability or
machine independence.

 Third generation languages were the first one that relaxed programmers from
writing programs in machine and assembly languages.

 A programming paradigm is a fundamental style of programming regarding how
problems solutions are to be formulated in a programming language.

ANSWER OF THE CHECK YOUR PROGRESS :

1. Characteristics of Information–Information incorporatesthe following charac-
teristics :

 meaningfulness  surprising element Check Your Progress:
5. DefineAlgorithm.
 conformity with previous  correction to previous 6. What doyouunderstandby
knowlknow knowledge
Bottom-up-design.
 brevity  accuracy 7. Name t he cat egor y i n

 timeliness  action oriented. whi ch progr aming lan-
guages can bedivide.
2. A program or a computer program isa collection of instructionsthat describes 8. Define"C" Language.
a task, or set of tasks to be carried out by a computer. Formally speaking, a
program is an expression of a computational method written in a computer 247
language.

3. While writing a program the following six activities are included :

a) Understanding Program Specification

b) Designing a Program Model.

Fundamentals of c) Determining Correctness of the Program.
Computers & d) Coding the Program.
Information Technology e) Testing and Debugging the Program.
f) Preparing Documentation of the Program.
NOTES 4. Debugging–Debugging is a process of identifying the main reason behind the
error and removing it. It is quite opposite to testing, which is a preliminary way
248 of finding the errors.
5. Algorithms are step-by-step commands which are used to complete task of
your choice. Every command in algorithm is known as step while is program-
ming languages, it is generally called statement.
6. Bottom-Up Design–Thistechnique of designing a solution isjust reverse of top-
down design technique. It starts from lower level component to higher one. It
first designs the basic components and from these basic components it designs
higher level components. Every higher level component uses the lower level
component.
7. The programming languages could be broadly divided into two categories:
(i) Low Level Language
(ii) High Level Language
8. C – C language was developed in 1972 at AT & T Bell Laboratories in America.
It was developed by Dennis Ritchie. The name was derived from its earlier
versions B and BCPL. Today it is widely used in software developments. Apart
from this, it is related with UNIX which has increased its uses. Several built-in
programsof Unix were written in C language. C language isa powerful language
because it provides the data address in the memory.

EXERCISE

1. What do you mean by a programming language ? How is it different from a
natural language?

2. What is a program ? Define data and information.

3. Write five most important characteristics of information.

4. How many types of a programming language are there ? Elaborate them.

5. What do you mean by machine level and assembly language ?

6. Elaborate third and fourth generation languages.

7. What are the steps involved in developing a program ? Clarify them.

8. What is a programming paradigm ? How is it important ?

9. What do you mean by object oriented programming ?

10. Write short notes on the following -

(i) BASIC (ii) C

(iii) FORTRAN (iv) C+ +

(v) Java (vi) PASCAL

(vii) Visual Studio.NET (viii) Sun Studio One

11. What do you understand by pseudocode ?

12. Explain flowchart and symbols used in a flowchart.

13. What do you understand by structured programming ?

14. What do you understand by object oriented programming ?

14 Virus Virus
NOTES
The Chapter Covers :

 Introduction
 Virus
 History
 Mechanism of virus
 How A VirusSpreads
 How isvirus named
 A few Prominent Viruses
 Typesof Computer Virus
 Related Concepts:
 Anti VirusPrograms
 Norton Anti - Virus(nav)
 Execution of NortonAnti-Virus
 Summary
 Exercise

INTRODUCTION

The name of virus is enough to scare any user. No computer in the world is protected from
virus. Virus infect the computer in many ways and are of various types. There are many
programs to stop them. This chapter will deal with the information about virus in detail.

249

Fundamentals of VIRUS
Computers &
Information Technology Usually when we come across the term virus we are mistaken of the virus we suffer from
and get ill with flu and like that. It is actually not. Virus in terms of computer is not a living
NOTES organism which affects our body. It is named after such because of its characteristics.
A computer virus, in real, is a tiny program which when enters a computer, gets associated
250 with pre-installed programs and applications and induces malfunctioning the programs.
Like virus (biological organism) which enters a human body affects severely his health.
Similarly a computer virus (a program) when enters the computer destructs the proper
working of a computer. It can affect working of a computer in the following ways -

 by destroying important information in the computer.
 by making change in directories.
 by formatting floppy or hard disk.
 by diminishing the speed of computer processing.
 by altering the function of the keys on keyboard.
 by altering the data stored in programs and files.
 by stopping or hindering the execution of files.
 by flashing irrelevant messages on screen.
 by hindering the booting of a computer.
 by altering the size and structure of files.

When a virus affected program is executed, the virus executes itself in the primary memory
of the computer.

HISTORY

The word virus was, first, used by Fred-cohen, a student of California University, in his
research paper. The student showed in his research paper how the computer program
should be written which can enter a computer and attack its system just as virus enters
our body and infects it.
First, it is very difficult to find out computer virus. People didn't know about it till the
decade of 1980, and they denied the existence of such a program which can harm the
computer.
(C) Brain is supposed to be the first modern virus which spread on a big level in the whole
world. It created a news because it contained the name, address and the privilege year
of the person who created this virus. That program contained the name and complete
address of two pakistani brothers - Basit and Amjad and their company. At that time virus
was a new thing so people didn't think about it seriously.
In the beginning of 1988, Macintosh Peace Virus emerged. This virus was from Richard
Brandow, the publisher of a Montnel based magazine MacMag. This virus was specially
developed to hamper the Macintosh Operating System and on 2nd March, 1988 the
following message came on to the screen.
Richard Brandow, Publisher of MacMag, and its entire staff would like to take this oppor-
tunity to convey their Universal Message of Peace to all Macintosh users around the world.
Viruses kept coming with the passage of time and to avoid them the user started thinking
of a solution and then anti-virus software came into existence which is an industry in itself.

But the faster the anti-virus software came into existence, the more viruses were invented. Virus
When anti-virus software industry was reassured that it had achieved the aim of controlling NOTES
viruses then only macro-virus came into existence. Normal virus were used to infectes
executable files and system area while Macro virus started infecting files in Microsoft word 251
and this led to a large scale problem as generally people exchange files written in MS-
Word through e-mail. Macro virus were capable of causing more harm than the normal
virus. They directly attacked the application program resulting in huge loss of data. This
compelled the anti-virus industry to develop a new type of anti-virus.

MECHANISM OF VIRUS

After knowing about virus and their history let us know how they work. It is computer
program which can duplicate itself. But, since, virus is a computer program it too has its
limits. Virus can do as much as it has been instructed by its programmer through program.
For example, a Michael Angelo virus destroys a data on March 6 as the programmer has
instructed it to ensure, first, it is 6 march and if he ascertains that it is 6 March it displaces
the disc sector with the given instructions.
Unlike other programs a virus can duplicate itself. Generally a program duplicates itself
when we issue an instruction as we give copy command to make a copy of a specific file.
We also know, that no command can be executed themselves, till we issue such an
instruction. Likewise a virus program is either executed directly by the user or when
another program is executed by the user. Now the questions is why a user will execute
a virus on his own computer. For it, virus creaters use a technique so that the user can
be be fooled to execute the virus. In most of the situations, virus are present in already
existing executable file. When that file is executed the virus codes too are executed.
Once the user execuets the virus program, it spreads in the entire system and as per the
instructions available in the program it start damaging the entire system. Usually the virus
program gradually start copying themselves in other executable files; and when these files
are executed by the user, then they start spreading on the entire system.
Therefore, the virus needs to be executed to infect a system or program.

HOW A VIRUS SPREADS

A virus is a communicable program. It may be propagated by one of the following reasons.
 Using a pirated software – When a user acquires a program illegally it is called a

pirated software. A pirated software has maximum probability to be infected from
viruses as it comes from unauthentic sources and wherever the pirated softwares are
used, they carry viruses.
 Through Network System – On the network when one client gets affected and it
is shared with other clients then this causes infection spread among all the shared
clients.
 Through Secondary Storage Devices – When a file is copied from a virus affected
computer through secondary storage devices, virus also gets communicated to that
very system.
 Through Internet – Presently, Internet is supposed to be the most critical carrier of
viruses. Virus making people also use this medium frequently for their ill - venture of
spreading viruses.

HOW IS VIRUS NAMED

The typically beautiful names of viruses like Lucifer, Eddie, Disk Washer amaze the user
after all how they are named.

Fundamentals of In most of the examples, viruses are named by the people who find them. Anti-virus
Computers & programmers decide the name on the basis of virus code, their work, the size of virus
Information Technology code, their additional impact and the message sent during virus load. Even, after consid-
ering all these factors the appropriate name of the virus on that basis is not available then
NOTES it is given any name by the anti-virus programmer for the sake of identifying it. For
example, Disk Washer was named on the basis of its internal message, "From Dish Washer
252 with Love."
At times, it happens two working anti-virus professionals come to know about the same
virus at the same time. In such a condition, the single virus is known by two names, for
example, V3000 which was named by McAfee Scan, is also known as GumNam which
can be scanned by Nashot.
To save a user from the problem of multi-naming of a single virus, the computer Anti-virus
Research Organisation, if such dispute takes place, give a standard name to the virus by
which it is known all over the world. But before CARO names them they are known by
different name but when CARO give them a standard name then all those names are
known as there aliases.

A FEW PROMINENT VIRUSES

Today our computer is infected with several types of viruses. Everyday new types of viruses
are developed. The development of Internet has given a new dimension to the spread of
virus. Numerous sorts of viruses are infecting the computers today through net.
In this section, let us in this section, know about some very popular viruses which have
infected the computers at a very large scale.
M i chelangel o
By far the most famous computer virus around, the Michelangelo virus is so named
because it wipes out the data in the affected hard disk on the 6th of March (Michelangelo's
Birthday). It is also referred to as the 'March 6 virus' by some virus preventives. The virus
was first discovered in the middle of 1991 and nearly all virus preventive softwares
developed after its discovery were capable of correctly removing this virus. This is one of
the most well-known viruses largely because many antivirus researchers (wrongly) pre-
dicted widespread doom affecting the computer users on March 6th. The technical jour-
nalists in the industry went wild (what with a fancy name like Michelangelo) and predicted
millions of infected computers, enormous loss of data and the precise date on which this
catastrophe would occur. The hype that built up to March 6th collapsed when nothing
actually happened on that date. Some reports which came up later mentioned that the
estimates of the number of infected computers were in all probability highly exaggerated.
But Michelangelo remains the favourite of the media, even in India, where Michelangelo
reports continued right fill 1994. It is only recently that the hype surrounding the virus has
died down.
Diskwasher
The DiskWasher virus, so named because it contains a message having the term 'DiskWasher',
is a highly destructive virus that was first noticed in India in the latter part of 1993. The
virus would wait until the disk has been accessed a specific number of times and would
then proceed to low-level format of the hard disk. During the formatting process, the virus
displays the text 'From DiskWasher with love' repeatedly on the screen.
Since the virus only waited for around 5000 accesses before proceeding to format the disk,
in most cases, the virus destroyed the data on the disk even before it had a chance to
spread. In fact the virus was so destructive that it formatted itself out of existence and
today is rarely found in the wild. All anti-virus software created from 1994 onwards detect
and remove the 'Disk Washer' virus.

C-Brain Virus
Amzad and Basit two pakistani brothers developed this virus in January 1986. However, NOTES
it is not certified that this virus was created by the two brothers. It is considered because
the virus contained the true address of those two brothers. It's purpose was to discourage 253
people from buying software illegally. It is supposed to be the first virus of the world.
Additionally it was the most popular virus among all viruses which had infected lacs of
computers. It was a boot-sector virus.
Macmag
The particular thing about this virus was that it didn't appear to be a virus. It ended on
your monitor with a peace message. One more specific thing about this virus was that it
infect, only Apple macintosh computers Richard Bramdow is supposed to be the fatch of
this virus. Richard Macmag is the publisher of a magazine and the virus was named after
this magazine. It did caused much damage but the terror which it had created, wasted
some time resulting in some loss.
Jenusalem
This virus was first found in Hebrew university Jerusalem. Therefore it was named Jerusa-
lem. It got active only on fridays. It was a very dangerous virus. This virus used to delete
all those file on which work was performed on fridays. It destroyed executable files with
the extensions .com and exe.
Columbus
Columbius virus is also known as Datacrime and 13 October. It was named 13 October,
as it became active on all the infected computers only on 13 October 1989. It, like
Jerusalem, infected the executable files and destroyed the data on the hard disk.

TYPES OF COMPUTER VIRUS

Viruses can be classified into many categories. They are classified as follows on the basis
of their style of affecting the computer system -
 Boot Sector Virus :

These types of computer viruses get themselves stored in the boot sector of floppy and
hard disk. When we boot a computer system it hinders the loading of operating
system. If somehow Operating System becomes operative, then it starts affecting the
other storage devices of the computer.
 Partition Table Virus :
These kind of viruses affect the partition table of hard disk but do not affect the data
in the computer.
It only affects MBR - Master Boot Record of the hard disk which may have following
consequences :
 This virus executes itself on the high priority place in MBR.
 It decreases the capacity of RAM.
 It affects the I/O stream of disk which leads to the malfunctioning of I/O pro-

grams.
 File Virus :

This kind of virus gets associated with executable files. When an EXE file is executed,
virus also executes to affect the computer system.

Fundamentals of  Stealth Virus :
Computers & A stealth virus is a computer virus that makes every effort to conceal its presence from
Information Technology the user. The techniques range from hiding the increase in size of an infected file from
the user, all the way to infecting the disk in multiple areas so that simply removing
NOTES the infection from one area does not actually remove the virus.

254  Polymorphic Virus :
A polymorphic virus is one that is capable of changing itself so that each infection of
the virus is completely different from the original. It is very difficult to check such
viruses since every time they are completely different.

 Macro Viruses :
A macro virus is a virus specially meant to infect specific type of file such as document
file and spreadsheet file. Micro viruses disguised as macro (a special program contain-
ing set of commands for execution of a particular task in the very softwares), can
damage data when used.

RELATED CONCEPTS :

Apart from real computers viruses, there are some virus like programs which damage the
system, though they do so differently. Therefore we must know about these concepts. This
chapter throws a light on these principles.
TROJANS
A 'trojan' is a program that claims to do something useful or interesting, but in effect does
something harmful ( like formatting the hard disk ) when actually runs. Some trojans do
not perform their action immediately but delay their harmful act based on the specific
situation (like a date or when the hard disk becomes half-full).
Since a trojan never duplicates itself, it cannot be said to be a computer virus. However,
since a trojan performs potentially harmful activity and since it is easier to write a trojan
than an actual virus, plenty of learner virus writers create trojans instead. In some cases,
trojan programs have been used as a 'dropper' to actually release a new virus when run.
To persuade users to utilize the trojan, the program is usually attributed to a known
computer expert or a well-known computer program. Examples of trojans include the
recent PKZ300 trojan that many users downloaded from the Internet, thinking it to be the
latest version of the popular PKZIP program.
BOMBS
A bomb is a routine hidden inside a normal program that can intentionally cause it or
other programs to malfunction under certain conditions. Bombs can be inserted by an
angry employee or as a prank. One common example quoted is that of a company
inserting code into its programs so that if a pirated copy of it is used, the code would
delete the pirated copy from the hard disk. Just like viruses and trojans, bombs are also
despised by the computer user community due to the potential danger involved.
An ANSI bomb or a Letter bomb is a displayable text material that contains ANSI key
redefinition codes that reprogram the keys to perform harmful activity. ANSI codes are
given by displaying certain escape sequences to the screen. Therefore the key redefinition
can take place by simply displaying the text material on the screen say by using the 'TYPE'
command. For example, an ANSI bomb could redefine the F3 key to a format command
and the user pressing the F3 key would cause the disk to be formatted.
WORMS
A 'worm' is similar to a virus in the sense that the worm propagates by duplicating itself.
The difference is that while a virus infects other executable files, a worm usually exists as
a stand alone program. The best example was the 1988 Robert Morris Worm program that

was executed on one or more hosts connected to the Internet. This program proceeded Virus
to collect the host, network, and user information and then utilizing this information, NOTES
broke into other machines. The Worm utilized flawsin the system to infect Sun Microsystems'
Sun 3 systems, and VAX computers running variants of 4 BSD UNIX. After breaking in, the Check Your Progress:
program would attempt to replicate itself and the copy would also attempt to infect other 1. What isVirus?
systems in a similar manner. While this Worm was not written with malicious intent, it had 2. How a virus spreads ive
an undesirable side effect. The infected systems became overloaded with running pro-
cesses as they became repeatedly infected that, as time went on, some of these machines some reasons ?
were unable to continue with any further processing and had to be shut down. 3. What isBoot sector virus?
EMAIL-HOAXES 4. What is filevirus ?
A new kind of hoax is being perpetrated among the Internet community in general. By
1994, the non-technical computing users on the net had increased enormously. The easy 255
availability of information, combined with the gullible non-technical users who were
online, led to the creation of the e-mail hoax.
The concept of an e-mail hoax is simple. Somebody sends out a mail, warning users about
a new kind of virus and asks users to tell all their friends about it. The mail may also
contain technical information which manages to just about sound plausible and also quote
some kind of authority to persuade the user regarding the authenticity of the mail. The
unsuspecting user immediately decides to inform his friends about it. Assuming every user
on an average sends out 5 copies of the letter, it is quite easy to calculate that after around
10 cycles, the number of mails being sent would amount to 510 letters or 9765625 letters.
Imagine the enormous waste of time and money involved! And, sooner or later, friends
who received the mail from other sources would start sending you the mail resulting in
multiple copies of the same mail tying up your mailbox.
In short, any E-mail that informs you about a virus and asks you to inform all your friends
about it is most likely to be a hoax.
COMPANIONS
Companions is a harmful program, it does not damage executable files, on the contrary,
it creates a completely different file with the same name with .com extension. When a
user executes an executable file then in place of the real file the codes of the companion
program are executed and their instructions generate harmful results after getting activated
in the computer.

ANTI VIRUS PROGRAMS

It is interesting to note that the arrival of the computer virus generated a whole sub-
industry of software development concentrating on providing software antivirus tools to
the user. It is also interesting to note that most users prefer to think that it is the antivirus
guys who themselves create and release viruses. After all, aren't they the ones who profit
?
In fact, most antivirus personnels know perfectly how harmful a virus is, and the potential
for damage involved, and would refrain from doing any such thing. However, every
industry has its black sheep and it is indeed possible that all antivirus personnels may not
have the same high moral standards. Most antivirus personnels have accumulated highly
specialized knowledge about viruses; so they admittedly have the knowledge to churn out
highly complicated viruses. However, it should also be noted that most of the viruses that
are crop up by the dozen are actually quite simple viruses or variants of existing ones. This
just confirms belief that most viruses are actually created by people who are learning
assembly language and do not realize the problems that their creations can actually cause.
PREVENTERSAND CHECKSUMMERS
One category of antivirus programs deals with preventing the virus from entering the
system. The notion is that if the system can not be infected, viruses will never spread.

Fundamentals of These preventors work either by scanning for specific virus signatures during program
Computers & execution or by looking for virus like behaviour. While the benefits of having a preventor
Information Technology is unquestionable, this type of approach has many inherent drawbacks.
A preventor takes up memory for its own use, slows down the system ( since it scans for
NOTES viruses during program execution ) and may not catch the newer viruses. However, this
type of approach is useful as a short-term remedy to completely get rid of a persistent virus
256 infection.
Most of the antivirus packages come along with a prevention program that is capable of
defecting the virus before the system becomes infected. For example, Nashot Antivirus
package comes with the 'NashMem' preventor.
CheckSummers are used to report the change in contents of executable files in the system.
When a new virus infects the system, it has to necessarily make modifications either to
the system areas (boot/partition sector) or to the executable files present in the system. The
CheckSummer keeps track of a CheckSum or CRC ( Cyclic Redundancy Check ) associated
with each executable file and informs the user when a change happens.
Unlike Preventors, CheckSummers do not prevent the infection from taking place, but
they do help to keep track of any unauthorized modification to executable files and system
areas by a virus. In short, a CheckSummer can only inform the user about the modification
that have happened. CheckSummers are not perfect since some of the newer stealth
viruses have the ability to filter themselves out of the files when they are being
CheckSummed. Most preventors also include some sort of CheckSumming facility.
SCANNERS
Scanner programs check for the presence of virus signatures either in memory or program
files and can tell you if your system is infected or not. Most scanners perform both a
memory and a file scan. Scanners do not remove virus, they merely report the presence
of the infection. As a result, some antivirus companies give away their scanning software
as freeware, so that the user would be able to evaluate the product. Of course, if you want
to remove an infection, you will have to buy the product.
Most scanners merely check for the presence of the virus signature in the files. Some
scanners also include heuristic scanning - which is also capable of detecting most new
viruses. However, all scanners which support the heuristic method of scanning also pop
up a warning message about possible misdetections.
Since the signature being scanned for is merely a set of bytes, it is entirely possible that
the same set is present in memory or in a file as possible data or even code statements.
Seeing the set of bytes (i.e., the signature) the scanning program will misreport it as a virus
infection. This is referred to as a 'false positive' match in the antivirus community. Examples
of scanners include Scan by McAfee and NashScan by Nashot.
REMOVERS
If any computer system is affected by virus then there are remedies to wash off the virus.
These are special computer programs or software which are used to detect virus by
scanning the whole system, and later repairing it by removing the viruses. These are called
anti virus programs.
The most popular anti virus program is NORTON ANTI VIRUS or NAV in short.

NORTON ANTI - VIRUS (NAV)

It is a very powerful software which can detect and remove almost every kind of computer
virus. It can also check the virus from Internet through e-mail. If this anti-virus is executed
with the booting and kept remain executing till the computer is on, it checks the virus
from being executed as and when a file is received or executed. It filters all incoming files
through e-mail to stop them entering computer system.

EXECUTION OF NORTONANTI-VIRUS Virus
NOTES
When you click the "Norton Anti-Virus" in program menu, a scheduler window appears
on screen. This window has a "SCAN" button; which on being pressed executes the NAV.
Execution comprises detection and removal of viruses from files and programs from the
computer. (See Figure 14.1)

Figure 14.1 : NAV scanning your computer

SUMMARY Check Your Progress:
5. H ow wil l you defi ne a
 A computer virus is a tiny program which when enters a computer gets associated
with preinstalled programs and applications and induces maling functioning in the worm?
programs. 6. What t ask per for m by

 Virus can affect working of a computer by destroying important information, by scanner programs?
making changes in directories, by formatting floppy or hard disk, by diminishing 7. Name most popul ar
the speed of computer processing and so on.
Antivir us program.
 When a user acquires a program illegally it is called a pirated software.
257
 A pirated software has maximum probability to be infected from viruses.

 Presently, Internet is supposed to be the most critical carrier of viruses.

 A stealth virus is a computer that makes every effort to conceal its presence from
the user.

 A polymorphic virus is one that is capable of changing itself so that each infection
of the virus is completely different from the original.

 A Macro virus is a virus specially meant to infect specific type of file such as
document file and spreadsheet file.

 The Michelangelo virus is so named because it wipes out the data in the affected
hard disk on the 6th of March (Michelangelo's Birthday).

Fundamentals of  The disk washer virus, so named because it contains a message having the term
Computers & 'Disk Washer', is a highly destructive virus that was first noticed in india in the
Information Technology latter part of 1993.

NOTES  A 'trojan' is a program that claims to do some thing useful or interesting but in
effect does something harmful (like formatting the hard disk) when actually runs.
258
 Since a trojan never duplicates itself, it cannot be said to be a computer virus.

 A bomb is a routine hidden inside a normal program that can intentionally cause
it or other programs to malfunction under certain conditions.

 Bombs can be inserted by an angry employee or as a Prank.

 A 'worm' is similar to a virus in the sense that the worm propagates by duplicating
itself.

 The concept of an e-mail hoax is simple. Somebody sends out a mail, warning
users about a new kind of virus and asks users to tell all their friends about it.

 Any e-mail that informs you about a virus and asks you to inform all your friends
about, it is most likely to be a hoax.

 Most antivirus personnels have accumulated highly specialized knowledge about
viruses; so they admittedly have the knowledge to churn out highly complicated
viruses.

 A preventor takes up memory for its own use, slows down the system (since it
scans for viruses during program execution) and may not catch the newer
viruses.

 Most of the antivirus packages come along with a prevention program that is
capable of defecting the virus before the system becomes infected.

 The most popular antivirus program is NORTAN ANTI VIRUS or NAV in short.

ANSWER OF THE CHECK YOUR PROGRESS :

1. A computer virus, in real, isa tiny program which when entersa computer, gets
associated with pre-installed programs and applications and induces malfunc-
tioning the programs.

2. Using a pirated software–When a user acquires a program illegally it is called
a pirated software. A pirated software has maximum probability to be infected
from viruses as it comes from unauthentic sources and wherever the pirated
softwares are used, they carry viruses.

Through Network System–On the network when one client gets affected and
it is shared with other clients then this causes infection spread among all the
shared clients.

Through Secondary Storage Devices–When a file is copied from a virus af-
fected computer through secondary storage devices, virus also gets communi-
cated to that very system.

Through Internet–Presently, Internet is supposed to be the most critical carrier

of viruses. Virus making people also use this medium frequently for their ill - Virus
venture of spreading viruses. NOTES

3. These types of computer viruses get themselves stored in the boot sector of 259
floppy and hard disk. When we boot a computer system it hinders the loading
of operating system. If somehow Operating System becomes operative, then it
starts affecting the other storage devices of the computer.

4. This kind of virus gets associated with executable files. When an EXE file is
executed, virus also executes to affect the computer system.

5. A 'worm' is similar to a virus in the sense that the worm propagates by dupli-
cating itself. The difference is that while a virus infects other executable files, a
worm usually exists as a stand alone program.

6. Scanner programs check for the presence of virus signatures either in memory
or program filesand can tell you if your system isinfected or not. Most scanners
perform both a memory and a file scan. Scanners do not remove virus, they
merely report the presence of the infection.

7. The most popular antivirus program isNORTAN ANTI VIRUSor NAV in short.

EXERCISE

1. What is computer virus ?

2. Write the differences between a biological and a computer virus.

3. Define boot sector virus.

4. What is Hoax ?

5. What do you mean by pirated software ?

6. When was Michael Angelo virus to be executed ?

7. Why was Disk Washer named so ?

8. Explain the functioning of Virus.

9. Write the probable causes behind virus infection.

10. Write about Jerusalem virus.

11. Explain Disk Washer virus in brief.

12. Internet is the major carrier of virus. Explain this statement.

13. Differenciate between WARM and Virus.

14. Write a short note on scanner.

15. Describe the history of virus in detail.

16. How is virus named ? Explain.

17. What do you mean by Companion and Bomb ?

Fundamentals of 18. Explain different sorts of viruses.
Computers & 19. What does anti-virus do ? Describe the functions of Norton Anti-virus.
Information Technology

NOTES

260

15 Communication Communication and IT
and IT NOTES

The Chapter Covers :

 Introduction
 Virus
 Computer Network
 Communication Process
 Communication Types
 Transmission Media
 WirelessMedia
 Communication Channels/Media
 Modem
 CharacteristicsOf a Modem
 Typesof Modem
 Summary
 Exercise

INTRODUCTION 261

Computer is the creator of information, but this information can not be useful for the
human being unless and until they are exchanged. Going back to the previous centuries
we know sending information took time much more than today. Today it takes not only
very less time but it is very much convenient too. Satellite and television have changed
the world into a village.
We have a number of options to communicate our messages and exchange our ideas.
They are as follows :

1. Letter
2. Telephone
3. Fax
4. Telegram
5. Internet
6. Telex etc.
Internet is such a powerful medium which can communicate our messages as well as
exchange our views across the world in a very short period of time and at a very low cost.

Fundamentals of Today, large scale factories, companies and offices are opening all over the world. These
Computers & companies and factories consist of several departments, all rely on each other. All the
Information Technology departments are equipped with computers in order to perform the operations at the
earliest possible. But information takes a lot of time in getting communicated. For ex-
NOTES ample, a factory has departments like purchase, sale, store and accounts. In this case the
department of accounts should have information related to purchase and sale. The same
way sale department should be aware of the store. Here, performance of work depends
upon the speed of information. Speedier the information , earlier the work will be. The
most powerful medium in this way is computer network. Computer network can keep you
update to a second.

COMPUTER NETWORK

Nowadays, computerized system of working is replacing manual system of working. In the
computerized system, interconnection of different computers with the help of any me-
dium is called computer network. With the help of computer network data can be
exchanged mutually. Computer network works according to a protocol which can be
removed if any problem occurs in data transmission. Computer network is a useful system
in which multiusers can use the same data and information collectively. Software programs
can also be shared on computer network.

Figure 15.1 : Computer network

Likewise on computer network, the computer devices, such as- disk, printer and micro-
processor can be shared. Therefore, a computer network stands for using internally con-
nected computers and devices in a group.
Computer network can be defined by the following criteria :
1. Devices share data and information with the help of a group communication medium

on network.
2. Network provides with the facility to check unauthorized users.
3. Network contains a particular address so that sent data from a device should reach

the concerned device only.
Computer network includes mainframe, personal computer and various other communi-
262 cation devices.

COMMUNICATION PROCESS Communication and IT
NOTES
Communication chiefly aims at exchanging data and information. Data communication is
meant by exchanging data between two different or similar devices.
Effects of data communication can be illustrated by three main properties.
 Delivery – Delivery means sending and receiving data from one place to the other.
 Accuracy – The property ensures reliability and accuracy of data.
 Timeliness – This ensures delivery of data at right time.
Communication process comprises five factors.

(i) Message
(ii) Sender
(iii) Medium
(iv) Receiver
(v) Protocol
The picture below illustrates communication process.

Figure 15.2 : Communication process 263

COMMUNICATION TYPES

Communication media are classified on the basis of directions of data transmission. In
communication media, data are transmitted at a time in one direction or both directions.
On this basis , it can be classified into three classes – Simplex, Half Duplex and Full
Duplex.
SIMPLEX
In this state of transmission, data or signals get transmitted in one direction. For example,
by computer connected keyboard, data is transmitted only from keyboard to computer.
Therefore Two-way transmission of data requires two lines. Though simplex line is cheaper,
it is inappropriate for computer based communication. Computer based communication
specially requires Two-way communication.
Even with the devices like printer, in which data are transmitted one way, it is inappro-
priate.

Fundamentals of
Computers &
Information Technology

NOTES

Figure 15.3 : Simplex mode
HALF DUPLEX
In this state, transmission is possible in two directions but at one time transmission is done
in one direction only. For example, from a hard disk, data are exchanged in a half duplex
state. When data are saved onto hard disk, data can not be read from hard disk likewise
while reading data, it can not be saved onto that.

Figure 15.4 : Half duplex
FULL DUPLEX
Full Duplex lets data transmit in both directions. Special purpose telephone lines avail this
facility.
Computer to computer hardware communication uses full duplex state. In this state, a lot
of data transmission takes place same time in both direction.

Figure 12.5 : Full duplex
TRANSMISSION MEDIA
In this medium, computers are connected to a network or they are inter-connected using
metal wire or optical fibre of glass. Physical connections are of three types :
 Twisted wire pairs – This is a cheaper communication medium. It is a pair of inter

twisted wires in which both wires are also made up of strands of metallic thin wires.
Twisted pair is made up of two copper conductors. Each conductor are with plastic
electric insulation and are twisted together. One of them is used to take signal to the
receiver and the second one is used for ground reference. The receiver uses the
264 difference between the two.

Communication and IT
NOTES

Figure 15.6 : Twisted wire pairs
Apart from the signal sent by the wire, noise and other sounds can affect both the
wires and unwanted signals are created.
If both the wires are parallel, the effect of this unwanted signal is not same on both
the wires. As both are on different locations with respect to noise and cross talk. It
means one is wire is nearer to noise and cross-talk while the other one is a bit away
from it which may create difference between the signals obtained by the receiver.
When the wire pair is twisted a balance is restored. Suppose in a twisted state one
wire is close to the noise and the other one is far and in the next twist condition, it
is reverse.

Figure 15.7 : RJ45 Connector

Because of the twist, both the wires are equally affected by an external effect (noise
or crosstalk). It means the receiver calculating the differences between the both gets
two unwanted signals. The unwanted signals are mostly cancelled.
It is now clear that the number of twists per unit affects the quality of the table.
Unshielded twisted pair is the most used twisted pair wire. RJ45 is the most popular
UTP connector. The complete name of RJis Registered Jack. It is a keyed connector,
therefore, can be inserted in a single way.
This technique of communication medium has been in use for a long time. This is
mostly used in telephone line.
Modem also uses this wire to get computer connected with a telephone line.

265

Fundamentals of Application of Twisted Pair Cable :
Computers & Twisted pair cables are used to provide data channel and voice in the telephone. The line
Information Technology linking the customer to the main telephone is made up of unshielded twisted pair. DSL
Line which presents high data rate connector by telephone companies uses high band-
NOTES width capacity of unshielded twisted pair cable.
Local Area Network such as 10 Base-T, and 100 Base-T also uses twisted pair cable.
 Co-axial cable – In this medium, copper wire is fixed in the centre of a metallic axial

and there is a layer of bad conductor matter in the centre of both. Coaxil cables are
used to send higher frequency signal than that of twisted pair cable. It is so because
both mediums have been prepared in a different way. Instead of two cables, co-axial
cable has a central conductor of a solid or standard cable, mainly made up of copper
and is covered with electric-insulation care that is wrapped with metal foil, stripe or
with conductor of both metail foil and stripe. The metal cable being wrapped on the
outside protects the cable from external noise and acts as the second conductor which
completes the circuit. Even this external conductor is covered with electric-insulator
and the entire cable is covered with plastic.
Twisted wire, at times interrupts communication and double voice is heard while
talking on telephone. To solve this problem co-axial cable has been devised. It is used
in very sensitive communication in which interruption may cause communication
badly like cable connection to television. Co-axial connectors are used to connect the
co-axial cables to the device. Bayone-Neill-Concelman or BNC connector is the most
popular connector.

Figure 15.8 : Co-axial cable

Application of Co-axial Cable :

These are used in Analog Telephone Network when one co-axial network was capable of
sending 10,000 voice signals, later it was used in Digital Telephone Network where it
could send 600 MBPS data. But, now a days telephone lines only use fibre optic cable.

Cable TV Networks too used Co-axial cable. Now they prefer Fibre optic cable. Now only
hybrid network used co-axial cable in Network boundary Cable TV uses RJ 59 co-axial
cable.

The other normal use of co-axial cable is in Ethernet LAN. Because of high bandwidth
capacity and high rate of data, co-axial cable are used in traditional ethernet LAN.

 Fibre Optic Cable – This is a modern technique of communication media. This cable
is made up of thousands of thin strands of glass in which light can travel. Each strand
is thin like a hair.

In this, for transmission, data is converted into light pulses and this light pulse of data
is transmitted with the speed of crores bits per second by a laser device. Each strand
is called a fibre. Hair like one fibre can send some television signals and thousands
of telephone line signals. Fibre optic cable is smaller and lighter than co-axial cable.
266 It is easy to use. Transmission is interrupted at the joints of two co-axial cables while

fibre optic joints are not even visible as after joining two fibre optic wires it becomes Communication and IT
one as it is sticken. In fibre optic ,the capacity of data transmission is ten times more NOTES
than co-axial cable. Co-axial cable weighs twenty times more than fibre optic cable.
In fibre optic cable data transmission is in condition which does not have any chance Check Your Progress:
of interruption. Hence, bit error in data transmission is zero. Electro magnetic trans- 1. What doyouunderstandby
mission of data has more errors and transmission is not clear.
acomputer Network?
Only three types of connectors are available for Fibre Optic Cables. Subscriber chan- 2. What arethe effect of data
nel connectors are used for Cable TV. It uses Push Pull Locking system. Straight Tip
connectors are used to connect the cable with networking device. It uses Bayonet communication?
locking system and is more reliable than SC. MTRJ is of the same size of RJ-45. 3. DefineHALF Duplex.

Applications of Fibre Optic Cable : 267

It is often found in backbone network for
its bandwidth is inexpensive. Nowadays
with Wavelength Division Multiplexing, we
can send data at the rate of 1600 GB per
second. Same Cable TV companies use
Fibre Optic Cable with co-axial cable to
create hybrid network. Optical fibre pro-
vides backbone structure while co-axial
cable provides connections to the user. It
is an in expensive configuration since, be-
cause of the necessacity of less bandwith
on the user's end the use of optical fibre
is not considered wire.

Fibre Optic Cable is used for LAN, such as Fig. 15.9 : Fibre Optic Cable
100 base- fx network (fast ethernet) and
100 base X network.

Advantage and disadvantages of Fibre Optic Cable

Advantages :

High Bandwidth – It supports very high bandwidth in comparison to other cables.
Currently, the use of data rate and bandwidth on Fibre optic is not restricted, but the
formation of signals and the available reception techniques fix its limits.

Less Signal Attenuation – The length of Fibre optic transmission is more than that
of other mediums. Signal, without regeneration can travel for 50 kms on fibre optic.
While, when we use co-axial or Twisted pair cable, after every five kilometres one
repeater is required.

Immunity to electromagnatic interference – Electromagnetic interference can't affect
Fibre Optic Cable.

Resistance to Corrosive materials – More prone to corrosive materials than glass,
copper.

Light weight – They are comparatively lighte than copper cables.

Greater Immunity to tapping – They are immune to tapping. Copper cables form
antenna effect which can be tapped very easily.

Disadvantages :

Installation and Maintenance – Being relatively newer, it needs expertise for instal-
lation and maintenance which is not available everywhere.

Unidirectional Light Propagation – Light has only one direction. If we need commu-
nication in two directions then we need two fibres.

Fundamentals of Cost – The cost of fibre optic cable and interface is more than other wire-mediums.
Computers & If high potential bandwidth are not in demand their use is not justified.
Information Technology
WIRELESS MEDIA
NOTES
It is also called unguided media. These media transport electromagnetic waves without
268 any physical medium. The signals are transmitted through free space, therefore, they are
available to everyone with a device capable of receiving them.
Wireless signals can travel from source to destination in several ways. These are ground
propagation, sky propagation and line of sight propagation. In ground propagation, radio
waves after touching the ground passes to the lowest part of the atmosphere. These are
propagated in all the directions with the help of less frequency transmitting antenna and
follow the curvature of planet. The distance depends upon the amount of strength of the
signal. The more the strangth the greates the distance. In sky propagation high frequency
radio waves radiate in ionosphere is the layer of earth's atmosphere, 80 to 1000 kilometers
above the earth's surface that sends back radio waves to earth from where they are sent
back to earth. Such transmission travel a greater distance with less output strength.
In line of light propagation, high frequency signals are transmitted from one antenna to
another in straight lines. The antennas are infront of each-other or so close to one-another
that the curve of the earth does not affect them. Line of light propagation is complex since
the radio transmission can't be focussed completely. Radio waves are microweb and
Infrared wireless Transmission media.
Radio Waves
It is a wireless medium. Though their is no perceptible limit between radiowaves and
microwaves still the electromagnetic waves with the frequency between 3 KHz and 1 GHz
are normally radio waves. And those between 1 GHz and 300 GHz are called microwaver
but for classification behaviour of waves is better standard than their frequency.
Radio waves move in almost all directions. When the antenna transmit radio waves they
are transmitted in all directions. It means the antenna sending the signal and the one
receiving the signal needn't be in a straight line. Waves are send by sender antenna that
are received by receiver antenna. It moves in all the directions which becomes its demerit.
The waves transmitted by one antena is very easily affected by the other antenna which,
just by using one frequency or band can send signals.
Low and medium frequency radio waves can pass through walls. This can be both merit
and demerit. It's a merit as an AM (Amplitude Modulation) Radio can receive signals inside
a building. It's a demerit as we can't restrict the communication to only inside or outside
of the building. Radio waves are narrower (within 1 ghz) than microwave band. When this
band is divided into sub-bands, even the subbands get narrower which leaves less data
rate for digital communication.
Almost entire band is controlled by the officers. One needs permission from the officers
to use any of their parts.
Applications of Radio Waves :
The all direction movement feature of radio waves makes them useful for multi-casting in
which there is one sender and many visitors. AM and FM radios, Television, Chordless
phone, are the examples of multicasting.
M i cr owaves
The Electromagnetic waves with the frequencies between 1 and 300 GHz are called
microwaves. Microwaves are the waves which move only in one direction. When an
antenna transmits microwave waves they can be focused limitedly. It means the sender
and the receiver antennas need to be in a straight line. This property of its is a clear
advantage. One pair of antena, without interferring by another pair, can be aligned straight.
Microwave transmissions have the following features :

 Microweve transmission is line of light Communication and IT
transmission since the antenna towers NOTES
should be in a straight line. The towers at
a remote distance should be very tall. If 269
the curve of the earth or other obstacles
become a hindrance between both the
towers, the shorter towers can't commu-
nicate using microweves. For long distance
communication only repeaters are re-
quired.

 Very high frequency microweves even
can't pass through walls. This symptoms
can prove to be its demerit if the receiver
is inside a building.

 Microwave bands are relatively wider. Figure 15.10 : Microwave controller
They are of almost 299 Ghzs. Therefore, applied to a oven
big sub bands can be assigned and these
high data rate becomes possible.

 To use a particular segment of the band, one needs permission from the officers.

Applications of Microwave :

Because of transmission only in one direction, Microweve are very useful when unicast
(one one one) communication is required between the sender and the receiver. These are
used in cellular phone, satellite network and wireless LAN.

Infrared

The Infrared waves with the frequency between 300 GHzs to 400 Tera Hzs (1 mm to 770
Nenometre wavelength) are used in small area communication. The Infrared waves of
great frequency can't pass through the walls. This advantageous system prevents interfer-
ence between two systems. The small range communication system of one room is not
affected by the other system in another room. While using owr infrared remote control
we don't hamper the use of remote by our neighbours. But the same symptom makes it
useless for long range communication. Addition we can't use infrared waves outside a
building as infrared waves are available in sun rays and it can hamper communication.

Application of Infrared :

There is good possibility of data transmission in the Figure 15.11 : Infrared
infrared band of 400 terahtz. The same kind of big directing PDA
bandwidth are used to transmit digital data at a very
high rate. Infrared data association is a union which
sponsors Infrared waves and have set standards for
communication between, key-board, mouse, computer
and printers. For example, a few manufacturers pro-
vide a special port named RDA in which chord-less
key-board communicate with PC. The standard de-
fines 75 KBPS data rate for basically 8 metres. The
latest standard define 4 MBPS data rate. RDA defined
Infrared signal are transmitted through line of site. The
RDA port of key-board needs to be pointed out to-
wards PC to start transmission.

COMMUNICATION CHANNELS/MEDIA

Data transmission between two devices is done in two ways:

(i) Parallel transmission

(ii) Serial transmission

Fundamentals of PARALLEL TRANSMISSION
Computers & Parallel transmission organises binary data in a group of bits and transmitted altogether. As
Information Technology we speak a word getting letters together, the same happens in parallel transmission.In
parallel transmission, each bit uses one wire to send one bit . 8-bits transmission requires
NOTES 8 wires as shown in the figure 15.12.
Parallel transmission possesses the advantage of speed. It transmits faster than serial way
of transmission but it is costlier than that.

Figure 15.12 : Parallel transmission
SERIAL TRANSMISSION
Serial transmission communicates data bit after bit as it is in 9 queues.

Figure 15.13 : Serial transmission
It is cheaper than parallel transmission. It is of two ways :
 Asynchronous Transmission
 Synchronous Transmission
 Asynchronous Transmission – In this Data transmission, stop bit and start bit are
added to data. It is just to inform the receiver about the start and end of the byte.
Bytes are used for data transfer in this type of transmission as shown in the figure
15.14.

270
Figure 15.14 : Asynchronous transmission

 Synchronous Transmission – In this very transmission, data are in frames consisting Communication and IT
of different sets of bytes. Receiver separates the bytes from the frame. Synchronous NOTES
Transmission has been illustrated in the figure 15.15.

Figure 15.15 : Synchronous transmission

MODEM

It stands for Modulation and Demodulation. It converts digital signals to analog ones and
vice versa. Infact, digital signals cannot be transmitted on analog phone line therefore
digital signals (1 and 0) are converted to analog . This process is called modulation.
Similarly, analog signals cannot get transmitted over digital media hence it is converted to
digital. The process is called demodulation.
Modem-Working and Characteristics
Digital symbols cannot be passed on analog phone lines therefore digital symbols (1 and
0) are converted into analog symbols. This process is called modulation. The same way,
analog symbols can't be sent on digital mediums, therefore analog symbols are turned into
digital symbols. This process is called De-modulation. There is a device to perform both
the process- Modulation and Demodulation which is called Modem. Modem is the short
form of Modulation and Demodulation. Modem is useful even when signals are weak
because modem enchances speed of data signals for data transmission at distant places.
It increases the speed before transmission of data signals.
Today, fibre optic modem are also available which can convert digital signals into optical
signals which can make data communication in Fibre Optic Cables possible. The modem
launched by AT&T is called Data Sets.
The Data Transfer Rate for Micro computers is 300, 1200, 2400, 4800 and 9600 bits per
second. The modems with even higher speed are also available today.

271

Fig. 15.16 : Modum- working

Fundamentals of CHARACTERISTICS OF A MODEM
Computers &
Information Technology There are two most important characteristics of a modem. They are transmission speed,
error detection and correction and compression. All three characteristics are being dis-
NOTES cussed ahead-

272  Transmission Speed

 Modems are available in different transmission speeds, which are measured

in bps (bits per second)

 Standard modems speeds are 9600 bps, 14400 bps, 28000 bps, 33600 bps,

56800 bps.

 Error detection and correction

 Nowadays most of the modems support advanced error detection proto-

cols at the hardware level.

 Detection and correction is achieved using such protocols as:

 Microcom Networking Protocol (MNP) – a protocol developed

by Microcom. It was developed to detect, and correct, errors
resulting from noisy telephone connections.

 ITU-T (International Telecommunications Standardization Sector)

is a home for various other protocols, known for their names
which start with a V (otherwise known as the V-Dot Standards)
eg. V.34: An error control standards for 28800 baud modems/
14400 baud faxes.

 Compression

 Due to the low transmission speeds achieved by modems, most modems

support a variety of data compression protocols.

 Using these protocols, the data throughout can rise by an average of

50%.

TYPES OF MODEM

There are mainly three types of modems. They are being discussed ahead.

EXTERNAL MODEM

External modem is a box that keeps Figure 15.17 : An external modem
modem circuitary outside the computer
system. This is connected to a com-
puter system using a serial port, uni-
versal serial Bus or a firewire port and
connected to a telephone line with a
standard telephone jack. This kind of
modem is on the verge of disappear-
ance from the market. (See Figure
15.17)

INTERNAL MODEM

Internal modem is a circuit board that is plugged into an expansion slot of the computer
system. Internal modem has one advantage that it does not occupy any space on the
desktop however, uses one expansion slot.
Nowadays, modems are coming in the form of PC cards. This kind of modem is used with
wireless or mobile phones and provide wireless transmission.

FAX MODEM Communication and IT
NOTES
Using fax modem you can send a fax from your computer as well receive a fax from others.
You can exchange faxed information from other fax modems or machines from other ends. Check Your Progress:
This has got one advantage that you can edit faxed information after converting them into 4. What are theadvantage of
files using an appropriate software.
Fibre OpticCable ?
SUMMARY 5. What are the applications

 Computer is the creator of information, but this information can not be useful of Microwave ?
for the human being unless and until they are exchanged. 6. Definemodulationandde-

 Internet is such a powerful medium that can communicate our messages as well modulation.
as exchange our views across the world in a very short period of time and at a 7. Namethetypesof modem.
very low cost.
273
 Nowadays, computerized system of working is replacing manual system of work-
ing.

 Devices share data and information with the help of a group communication
medium on network.

 Network provides with the facility to check unauthorized users.
 Network contains a particular address so that sent data from a device should

reach the concerned device only.
 Communication chiefly aims at exchanging data and information.
 Communication media are classified on the basis of directions of data transmis-

sion. In communication media, data are transmitted at a time in one direction
or both directions.
 In simplex state of transmission, data or signals get transmitted in one direction.
 In half simplex state, transmission is possible is two directions but one transmis-
sion is done at one time in one direction only.
 Full Duplex lets data transmit in both directions. Special purpose telephone lines
avail this facility.
 Twisted wire pairs is a cheaper communication medium. It is a pair of inter
twisted wires in which both wires are also made up of strands of metallic thin
wires.
 Modem also uses twisted wire to get computer connected with a telephone line.
 In co-axial cable medium, copper wire is fixed in the centre of a metallic axial
and there is a layer of bad conductor matter in the centre of both.
 Twisted wire, at times interrupts communication and double voice is heard while
talking on telephone.
 Parallel transmission organises binary data in a group of bits and transmitted
altogether.
 Serial transmission communicates data bit after bit as it is in 9 queues.
 In asynchronous Data transmission, stop bit and start bit are added to data.
 Modem stands for Modulation and Demodulation. It converts digital signals to
analog ones and vice versa.
 Similarly, analog signals cannot get transmitted over digital media hence it is
converted to digital. The process is called demodulation.
 There are mainly three types of modems.
 External modem is a box that keeps modem circuitary outside the computer
system.
 Internal modem is a circuit board that is plugged into an expansion slot of the
computer system.
 Using fax modem you can send a fax from your computer as well receive a fax
from others.

Fundamentals of ANSWER OF THE CHECK YOUR PROGRESS :
Computers &
Information Technology 1. Interconnection of different computers with the help of any medium is called
computer network. With the help of computer network data can be exchanged
NOTES mutually. Computer network works according to a protocol which can be re-
moved if any problem occursin data transmission. Computer network isa useful
274 system in which multiusers can use the same data and information collectively.
Software programs can also be shared on computer network.

2. Effects of data communication can be illustrated by three main properties.

 Delivery – Delivery meanssendingand receivingdata from one place to the other.

 Accuracy – The property ensures reliability and accuracy of data.
 Timeliness – This ensures delivery of data at right time.

3. Half Duplex–In this state, transmission is possible in two directions but at one time
transmission is done in one direction only. For example, from a hard disk, data are
exchanged in a half duplex state. When data are saved onto hard disk, data can not
be read from hard disk likewise while reading data, it can not be saved onto that.

4. Advantage of Fibre Optic Cable :

 High Bandwidth  LessSignal Attenuation

 Immunity to electromagnatic interference  Resistance to Corrosive materials

 Light weight  Greater Immunity to tapping

5. Applicationsof Microwave–Because of transmission only in onedirection, Microweveare
very useful when unicast (one one one) communication isrequired between the sender
and the receiver. These are used in cellular phone, satellite network and wirelessLAN.

6. It stands for Modulation and Demodulation. It converts digital signals to analog ones
and vice versa. Infact, digital signals cannot be transmitted on analog phone line
therefore digital signals (1 and 0) are converted to analog . This process is called
modulation. Similarly, analog signals cannot get transmitted over digital media hence
it is converted to digital. The process is called demodulation.

7. Types of Modem–There are mainly three types of modems :

(i) External Modem (ii) Internal Modem

EXERCISE

1. Write the uses of communication.

2. What do you mean by communication process ?

3. What is simplex ?

4. Define half duplex and full duplex.

5. What do you mean by parallel and serial transmission ?

6. What is a modem ? How many types of modem are there ?

7. Write a note on computer network.

8. Write the names of different modes of a communication channel.

9. Explain Transmission Media.

10. Explain Wire-Media and Wireless media.

11. Explain Twisted pair cable in detail. Write about it utility.

12. What are co-axial cables ? What are their functions ?

13. What is Fibre Optic Cable ? Write about its functions.

14. Write advantages and disadvantages of Fibre optic.

15. Explain Parallel and Serial Transmission.

16. What do you mean by Asynchronus and Synchronus Transmission ?

17. Write about the chief characteristics of Modem.

16 Networks Networks
NOTES
The Chapter Covers :
 Introduction
 Virus
 Internet VsIntranet
 Typesof Network
 Topology
 Typesof Connectivity
 Network Devices
 Summary
 Exercise

INTRODUCTION

Networks as studied in the last chapter enable computers get to connected mutually and
thus users can share resources available on more than a computer. There are various types
of arrangement of computers on a network and there are many devices that are used to
network the computers. This chapter presents maximum information required at this level.

275

Fundamentals of INTERNET VS INTRANET
Computers &
Information Technology Internet and intranet seem to be identical terminologies however they have some clear
differences. If you look at literary meanings of the two then probably the differences
NOTES would be clear. For example, you would have heard about inter schools competition.
Similarly, Intra school competition takes place. Both have a prominent difference. Inter
276 schools competition is held among several different schools while intra school does not go
beyond the school boundaries means this competition is supposed to be held among boys
and girls of that particular school only. Likewise, Internet consists of several wide networks
across the world. And intranet is limited to private network of a particular organization.
LAN can be thought as an example of Intranet to some extent. Internet and intranet have
one distinguished difference of its environment. Both sites are designed in a different way.
Both have different audience group. Both are different in their access speed. Both may
be different in their platforms and operating systems. Differences may be summarised as
follows -

 Internet always starts with capital I whereas intranet begins with small i provided the
sentence does not start with it.

 Internet is a network of networks. Most of business networks are usually internetworks
therefore they may be two or more Local Area Networks.

 Internetwork of a company consists of several different networks. Intranet of several
companies is extended within a specific building and others are located in its offices
across the globe.

 Internet presence of a company is built on different server groups. It serves both sorts
of public and private users.

 Intranet is a platform independent client/server computing network located within a
private inter-network. Intranet may be assumed as a private Internet, in that it uses
the same tools and services as Internet services, but for private use only.

 Intranets can have web sites, FTP servers and especially interactive client/server ap-
plications, just like on the Internet, except with greater speed, security and platform
independence.

 Designing a website for Internet is comparatively more difficult than designing websites
for intranet.

 While designing an Internet website size of files is kept small so that it can be
downloaded or accessed fast. Whereas, size of file in an intranet website does not
matter. Its file size may be large as its access speed is fast.
AA

G G BB

CC B

BB

CC

Figure 16.1 : Network A,B,C are equally connected to gateway G. Network A, B
and C may be assumed as a private network or intranet whereas the entire
structure can be understood as Internet

 Internet website works perfectly on a big series of browsers while intranet website is Networks
developed for a specific type of browser. NOTES

 In an Internet website frames are least used as search engines find difficulties to index
frames of the website. However, there is no problem in using frames in designing
intranet sites.

Apart from to all these, since Internet website is used by people all across the world with
diversified technologies and platforms. All these things are kept in mind while designing
such websites which is not applied in case of designing intranet sites. Figure 16.1 illustrates
differences between Internet and Intranet.

TYPES OF NETWORK

There are different types of network. They include mainly LAN, MAN, and WAN as being
dicussed ahead.
LOCAL AREA NETWORK
A Local Area Network (LAN) is a computer network covering a local area, like a home ,
office, or group of buildings. Current LANs are most likely to be based on switched IEEE
80 Ethernet running at 10, 100 or 1,000 Mbit/s or on Wi-Fi technology. Media commonly
used in LAN are coaxial cables, twisted wire pairs and also wireless.
Characteristics of LAN are :

 Much higher data transfer rates
 Smaller geographic range
 No requirement of leased telecommunication lines
 Limited number of computers can be connected only
LANs are capable of transmitting data at very fast rates, much faster than that can be
transmitted over a telephone line; but the distances are limited, and there is also a limit
on the number of computers that can be attached to a single LAN.

Figure 16.2 : Geographic area of Local Area Network 277

WIRELESSLAN (WLEN)
Wireless LAN is very common nowadays. The system of WLAN is based on a technology
known as WiFi which is an abbreviation of wireless fidelity. During the WLAN installation,
the distance is measured in feet and metres instead of miles as in other cases. Therefore,
this technology is not directly linked to ISP as in the line in the case of WWAN or satellite
connection but this can be used to link with any other LAN or equipment through which
Internet access can be obtained. In WWAN a wireless access pointer acts like a wireless
hub or switch. In a Wireless LAN, primarily a wireless access point is used that links
wireless computers to the wired LAN. Thus, users are able to exploit resources available
on LAN and using router they get connected to the Internet as well.

Fundamentals of To connect to the Internet, wireless access point, like any other device is linked to a wired
Computers & LAN and then the computers using wireless NICs are in position to access the LAN.
Information Technology Wireless access points can be bought with features like firewall routers and switches.
Wireless access point may be linked with the port of a standard hub or with a switch
NOTES associated with LAN.

router

Switch interface
Wireless Access

Point

Computer with
wireless NIC

Computer with Personal Digital Laptop
wireless NIC Assistant

Figure 16.3 : Wireless LAN

While mentioning the wireless LAN, it is also important to pen about hotspots. Hotspots
are public WLANs and available at airports, entertainment places, restaurants etc. for
providing access to the Internet for visitors in the range. However, there are risks in using
as they are open to public and hence quite unsafe.

METROPOLITAN AREA NETWORK

Metropolitan Area Network is a high speed network that can carry voice, data and images
at up to 200 Mbps or faster over distances of up to 75 km. Based on the network
architecture, the transmission speed can be higher for shorter distances. A MAN, which
can include one or more LANs as well as telecommunications equipment such as micro-
wave and satellite relay stations, is smaller than a wide area network but generally oper-
ates at a higher speed.

Characteristics of MAN are :

 Covers towns and cities

 Media used are fibre optic and cables

 Message routing is fast

278
Figure 16.4 : Geographic area of Metropolitan Area Network

WIDEAREA NETWORK Networks
A wide area network or WAN is a computer network covering a broad geographical area. NOTES
Contrast with local area networks (LANs) or metropolitan area networks (MANs) that are
usually limited to a room, building or campus. The largest and most well-known example
of a WAN is the Internet.

Figure 16.5 : Geographic area of Wide Area Network

WIRELESSWIDEAREA NETWORK
Wireless Wide Area Network is a digital network which is spread across vast global areas.
Wireless WAN receive and send the data through cellular sites and satellite radio signals
which in turn make the network accessible for mobile computer system. The wireless
WAN gets disintegrated into pieces or segments and then link with some public or other
network, through the telephone or some other speed communication link (See Figure
16.6).
The expansion area of coverage of Wireless WAN (WWAN) goes in miles and hence it is
very sensitive towards environmental factors and weather. WWAN is completely bi-direc-
tional having a speed of data processing at 100 Mega Bits Per Second (MBPS) or more.
In Wireless WAN, the signal starts from a centralized transmission unit of the service
provider. Through the medium of a cable, the company interfaces using the dish antenna.
This Dish antenna is linked with a transceiver equipment with the help of coaxial cable.
On the other side of transceiver, there is a port for ordinary CATS ethernet cable which
joins the LAN bridge containing multiport hubs. These hubs allow the speed of 100 MBPS
through the LAN.

Figure 16.6 : Wireless WAN 279

Fundamentals of VIRTUAL PRIVATE NETWORK
Computers & Virtual Private Network (VPN) can not have one clear cut answer. It can mean a lot of
Information Technology things, but the most common way to describe it as a private data network that transmits
data over the public telecommunication infrastructure. In essence, it is another “layer” on
NOTES top of an existing network.
For example, your company might require you to “VPN into” their corporate system while
you are at home or travelling. The reasons for this requirement are simple: Security,
Security, Security. VPNs allow you to securely access internal company resources from an
outside network as if you were sitting in your company’s building plugged into their
internal network. How is this done? IP Security. IP Security essentially encrypts every
packet of information sent between you and your company’s servers which can only be
read by either side with the appropriate “key”. As you might know, your internet traffic
frequently passes through dozens of hosts (or routers) before it arrives at its destination,
any of which would be able to “snoop” your traffic were it not encrypted.

Fig. 16.7 : Virtual Private Network
The Virtual Private Network (VPN) has attracted the attention of many organizations
looking to both expand their networking capabilities and reduce their costs.
The VPN can be found in workplaces and homes, where they allow employees to safely
log into company networks. Telecommuters and those who travel often find a VPN a more
convenient way to stay “plugged in” to the corporate intranet.
A VPN supplies network connectivity over a possibly long physical distance. In this respect,
a VPN is a form of Wide Area Network (WAN).
The key feature of a VPN, however, is its ability to use public networks like the Internet
rather than rely on private leased lines. VPN technologies implement restricted-access
networks that utilize the same cabling and routers as a public network, and they do so
without sacrificing features or basic security.
A VPN supports at least three different modes of use:

 Remote access client connections
 LAN-to-LAN internetworking
 Controlled access within an intranet
280

PROS AND CONS OF VPN Networks
Like many commercialized network technologies, a significant amount of sales and mar- NOTES
keting “hype” surrounds VPN. In reality, VPNs provide just a simple few clear potential
advantages over more traditional forms of wide-area networking. These advantages can be Check Your Progress:
quite significant, but they do not come for free. 1. Define L ocal Area Net -
The potential problems with the VPN outnumber the advantages and are generally more
difficult to understand. The disadvantages do not necessarily outweigh the advantages, work.
however. From security and performance concerns, to coping with a wide range of some- 2. What are main character-
times incompatible vendor products, the decision of whether or not to use a VPN cannot
be made without significant planning and preparation. sticsof MAN are?
Advantages of VPN 3. What are advantage& dis-

 Cheaper advantageof VPN?
 Network stability 281
 Easy to use
Disadvantages of VPN
 Complex Installation
 Weak VPN technology standard
 Internet based VPN is not under full control of organisation.

THE FUTURE OF VPN
The success of VPNs in the future depends mainly on industry dynamics. Most of the value
in VPNs lies in the potential for businesses to save money. Should the cost of long-distance
telephone calls and leased lines continue to drop, fewer companies may feel the need to
switch to VPNs for remote access. Conversely, if VPN standards solidify and vendor
products interoperate fully with other, the appeal of VPNs should increase.
The success of VPNs also depends on the ability of intranets and extranets to deliver on
their promises. Companies have had difficulty measuring the cost savings of their private
networks, but if it can be demonstrated that these provide significant value, the use of
VPN technology internally may also increase.

VPNS VS LEASED LINES
Organizations historically needed to rent network capacity such as T1 lines to achieve full,
secured connectivity between their office locations. With a VPN, you use public network
infrastructure including the Internet to make these connections and tap into that virtual
network through much cheaper local leased lines or even just broadband connections to
a nearby Internet Service Provider (ISP).

WIFI
Wi-Fi also known as wireless fidelity is the industrial name for wireless LAN (WLAN)
communication technology related to the IEEE 802.11 family of wireless networking stan-
dards. To some extent, the term Wi-Fi is synonymous with 802.11b, as 802.11b was the
first standard in that family to enjoy widespread popularity. Today, however, Wi-Fi can
refer to any of the three established standards 802.11b, 802.11a and 802.11g.
The Wi-Fi alliance certifies vendor products to ensure 802.11 products in the market
follow the various 802.11 specifications. Unfortunately, 802.11a is not compatible with
802.11b/g, so the Wi-Fi market remains somewhat fragmented.

Fundamentals of TOPOLOGY
Computers &
Information Technology Topology refers to the shape of network or the network’s layout. How different nodes in
a network are connected to each other and how they communicate are determined by
NOTES the network’s topology. Topologies are either physical or logical.

Simply defining, topology is the geometric arrangement of the computers in a network.
There are four types of topologies that prevalent across different networks.

RING TOPOLOGY

The ring network is a local area network (LAN)
having topology as a ring and has no host or
central controlling computer. Each computer is
connected with the nearest next computer and
becomes the subordinate of the former. In this
network there is no master computer. It is also
called circular network. Messages travel around
the ring, with each node reading those mes-
sages addressed to it.

Access and control of the network are main- Figure 16.8 : Ring Topology
tained by a token passing method. It is like
merry-go-round. Each computer passes message
to its closest computer and it goes on till the
message is not reached to the right computer.
Advantages of Ring Topology :

 This type of network can span larger distances than other types of networks.

 This network is more reliable as it does not depend on any central controlling
computer.

 If a particular line or computer stops working, network does not fail, it starts working
using line from another direction.

Disadvantages of Ring Topology

 Speed of this topology network is directly proportional to the number of computers
working under this network. Larger the number, less the speed.

 It is less trendy than star networks because this needs complex softwares to run it.

BU S TOPOLO GY

Bus networks have some similarities with ring networks. They have also no central con-
trolling computer. It is different as unlike ring networks their ends are not connected rather
than they are carried on a common cable or bus and are available to each device on the
networks.

282 Figure 16.9 : Bus Topology