An ISO 9001:2000 Certified Organization CS-611 COMPUTER FUNDAMENTAL & PC SOFTWARE BCA-1 IGNOU.

An ISO 9001:2000 Certified Organization

CS-611COMPUTER FUNDAMENTAL

& PC SOFTWARE

BCA-1 IGNOU

© Copyright PCTI Group 2009 | | <document classification>

BLOCK 1Computer Fundamentals:Hardware

& Software


Definition:

An electronic, digital device that stores and processes information.

Digitized Data(1010101010)

Final Result(example -Display of image)

Introduction


The tool known as ABACUS was the age-old tool used by

man to count and calculate was designed and developed by

Chinese some 5000 years ago.

Blaise Pascal designed a working mechanical calculator in

1642.

Gottfried Von Leibnitz a German, modified Pascal’s

calculating machine which could multiply numbers directly.

In 1833 Charles Babbage an English scientist, designed

Analytical Engine using tooth wheels so that it could perform

all mathematical operations in a predetermined sequence

using a set of operational instructions.

History


Lady Ada Lovelace is considered as the first lady Computer Programmer as she has developed the concept of writing systematic operational instructions for the analytical engine.

In 1850 George Boole an English mathematician proposed logic theory of using the binary (two) number system. This number system had (0 and 1).

Bool proposed a logic popularly known as Boolean algebra. Computer processors are designed on this system of logic.

A statistician Dr. Herman Hollerith, developed a punched card that would contain data coded in form of punched holes.

History


Computers have a very big impact on our day-to-day life.

They can be used for a number of applications like:

– Business

– Education

– Research

– Office

– Accounting

– Military

– Space

– Entertainment

– Medical

Applications of Computers


Following are the broad application

areas where computers are used

extensively

•Entertainment: It can be used to make cartoon

movies, animation and special effects in movies,

games etc.

•Day to day life: Collages, Hospitals, Railway and

Airline Booking Systems, Shops, Bank, ATM

centers etc. to carry out day to day work.

For example: Train ticket bookings

can be done with help of computer.



• Communication: Nowadays Internet is

becoming integral part of life to gather

information about different topics or to

send and receive emails etc.

• Scientist: use it for research purposes,

space programs, nuclear programs etc.

emails



• Speed: Computers carry out the jobs in microseconds or less time. The

human beings cannot think of doing the jobs in such speeds. Few lakh

calculations can be done in a second

• Accuracy: While doing a job human being may commit mistakes where

as if the data given to the computer is correct then the computer does

the job without any mistakes.

• Efficiency: Unlike the human beings efficiency is very high in

computers as it is a machine it does not get tired or bored of doing a job.

• Storage: Computer has memory in which the data can be stored for

future use. For example the details of the students, customers, suppliers

etc. can be stored in the computers to be used whenever it is required.

Advantages


• Computers cannot think by themselves and they require human

direction to perform specific tasks.

• If the data given is wrong then it gives the wrong result.

• Instructions given also should be correct that is instead of

addition if you ask it to multiply it will multiply.

• It will not work without electricity.

• Investment and maintenance in this equipment is also required.

Limitations


First Generation (1940-1956): Vacuum Tubes The computers of this generation were made of vacuum tubes for circuitry and magnetic drums for memory

Second Generation (1956-1963): Transistors The computers of this generation made up of transistors replacing vacuum tubes

Third Generation (1965-1971): Integrated Circuits The computers of these generations were made up of IC (Integrated Circuits)

Fourth Generation (1971): Microprocessors The computers of this generation saw the advent of Large Scale Integration (LSI) and Very Large Scale Integration (VLSI)

Generations of Computers


Personal Computers:

A microcomputer is the smallest general purpose processing system.

Minicomputers:A minicomputer is medium sized computer that is more powerful than a microcomputer.

Mainframes computers:Computers with large storage capacities and very high speed of processing.

Classification of Computers


Super computers: These have extremely large storage area and computing speeds, which are many times faster than earlier discussed machines.

Laptop/Note Book Computers:These are small in size and weigh few Kgs & you can carry any place.

Classification of Computers


Input Unit Output Unit

Control Unit

Main Memory

ALU

SecondaryMemory

Organization of a Computer


Any device designed to assist in the entry of data into a computer.

Mouse

Light Pen

Touch Screen

Joy Stick

Keyboard

Scanners

Optical Character Readers (OCR)

Magnetic Ink Character Reader (MICR)

Mark Sense Reader

Bar Code Reader

Input Unit


Any peripheral device that converts the stored binary coded data into convenient external forms as text, pictures & Sound

1. Visual Display Unit 2. Printer 3. Speakers

Output Unit


Arithmetic-Logic Unit (ALU): The ALU is an electronic

circuit used to carry out the arithmetic operations. (Addition,

Subtraction, Multiplication and Division)

Control Unit: The control unit coordinates the activities of all

the other units in the system.

Memory Unit: is used to store data temporarily.

Central Processing Unit


The storage capacity of the memory is generally measured in

megabytes.

8 Bits = 1 Byte

1024 Bytes = 1 Kilobyte (KB)

1024 Kilobytes = 1 Megabyte (MB)

1024 Megabytes = 1 Gigabyte (GB)


Memory

Memory is the main part of computer where we store our data either for temporarily or permanently

There are Two Types of Memory

1.Primary Memory

2.Secondary Memory


Primary MemoryWe can also called internal memory. This memory consists of semiconductor memory chips and is used to store the data and programs.

Two Types of Primary Memory

1.RAM (Random Access Memory) or Volatile Memory

2.ROM (Read Only Memory) or Non-Volatile Memory


This is the permanent memory. But user can delete

the data whenever they want.

Examples:

Floppy disks Fixed (hard) disks, Pen Drive Optical disks.

Secondary Memory


Secondary MemoryThis memory is external memory. This memory can store a large amount of data for permanently.

Types of Secondary Memory

1.Floppy Disk:- A floppy disk is made of flexible plastic material coated with iron oxide. This is used to store data and instructions. We can move the data from one place to another. The Floppy disks are available in two sizes 5.25 inches and 3.5 inches and their capacity range from 360 KB to 1.44 MB per disk.


2. Magnetic Disk:- A magnetic disk is circular platter of plastic which is coated with magnetized material. One of the key component of a magnetic disk is a conducting coil named as Head which performs the job of reading and writing on magnetic surface. The head remains fix while the disk rotates for reading and writing operation.


3. Winchester Disk:-

This is sealed rigid magnetic oxide medium disk, which holds 10 MB to 10 GB of data. These disks are not removable from the drive.


4.Magnetic Tape:-

Magnetic tapes are mounted on reels or cassette of tape to store amount of data. These are cheaper and removable from the drive. Information retrieval from tapes is sequential and not random. It takes long time for searching. They are low cost, low speed, portable.


5.Optical Memories

This memory is used to store a very-2 large amount of data. Data is written in optical disk through laser beam.

Three Optical Devices

1.CD-ROM

2.WORM

3.Erasable Optical Disk.


High Speed Memory

Cache Memory: These are small fast memories placed between the processor and the main memory.


Hardware: This comprises the Electronic,

Electrical and mechanical

components of the machine.

Software:Program means the set of

meaningful instructions written in

a particular order so as to carry

out some task.

Two important Computer terminologies


The term computer language includes a wide variety of languages used to communicate with computers.

Computer language is a system of communication.

The computer languages must have instructions to manipulate input/output, text etc.

Computer Language


These languages are broadly classified as :

Machine level language

Assembly level language

High level language

Fourth generation languages

Classification of Computer Language


Machine level language – A program written using binary numbers i.e. 0’s and 1’s specified for the processor’s operation and absolute binary address

Assembly level language -Language uses mnemonics or abbreviations to represent a particular operation.

High level language -

In this, instructions are written in simple English. (Examples: BASIC, COBOL, FORTRAN, PASCAL, C, C++ and Java etc

Fourth generation languages -

These are the application development tools, which improve the efficiency and productivity. Examples: DBMS, RDBMS

Classification of Computer Language


Two kinds of software are:

• System Software:

software control and direct the operation of the computer.Examples - Operating System, Compiler, and Interpreter

etc.

• Application Software:

software used for specific applications such as letter

typing, accounting, billing and inventory etc.

Kinds of software


Introduction to Operating Systems


Operating System

Operating system is an interface between user and machine. It is an essential component of computer system. The primary objective of an OS is to make computer system convenient to use and utilize computer hardware in an efficient manner.

An operating system is a large collection of software which manages resources of the computer system such as memory, processor, file system and input/output devices.


This is the system software, which acts as an interface between the user and computer.

All the computers require operating system without which one cannot work with the computer.

Operating system control, co-ordinates, synchronizes all the operations of the computer.

Examples: Microsoft Disk Operating System (MS-DOS), Microsoft-Windows 98, Microsoft-Windows XP, Microsoft-Windows 2003 Server, UNIX, LINUX etc.

Microsoft Disk Operating System

(MS-DOS),

Microsoft-Windows XP

Operating System


The main functions of Operating System are

1. Act as an interface between the user and the computer

2. To monitor the use of the resources of computers (Resources can be hardware or Software)

3. To control and coordinate Input and Output devices

4. It manage the program and data files i.e. to store, to retrieve, to delete files

5. Help the application programs execute commands given by the user

Functions Operating Systems


Examples of operating systems are • Microsoft Windows 98, Microsoft Windows XP, Microsoft

Windows 2000, Microsoft Windows 2003, UNIX, Linux, Novell Netware, Solaris etc.

Examples of OS


Evolution of Operating System

1.Serial Processing

2.Batch Processing

3.Multiprogramming


Different types of Operating Systems

1.Batch Processing System

2.Multiprogramming Operating System

1. Multitasking OS

2. Multi-User OS

3. Time Sharing System

4. Real Time System

3. Network Operating System

4. Distributed Operating System

Types of Operating System


Multiprogramming Operating System:-

The interleaved execution of two or more different and independent programs by the same computer.Multiprogramming is carried by placing the two or more user programs in main memory and executed them concurrently. The CPU switches from one program to another.


Multi-Processing:-A system that makes the use of more

than one CPU is called multiprocessing system. A multi-processing which describe interdependent computers with two or more independent CPU s have the ability to simultaneously execute programs. In this system, instructions from different and independent programs can be processed at the same instant of time by different CPU.


BLOCK 2Computer Fundamentals:

Communication, Networking, Security


BASIC TERMS

• Data are entities that convey meaning. Information is obtained by processing data using desired functions.

• Signals are electric or electromagnetic encoding of data,and signaling is propagation of signal along communication medium.

• Transmission is communication of data achieved by the propagation and processing of signals


DATA COMMUNICATION CODES (Data encoding)

• Computer manages, store and exchange data using electronic pulses or digital signals 0 or 1

0 1

OFF ON

(absence) (presence)

• Every char (letter, number, symbols) is composed of a group of bits called codes.


Data Codes

*American Standard code for information interchange

**Extended Binary coded decimal interchange code

ASCII* EBCDIC**

Controlling authority

Number of bits

Number of Character

ANSI

7

128

IBM

8

256


Communication Speed or Rate:-

• The speed at which two computers exchange or transmit data is called communication rate on transmission speed.

• The unit of measurement of speed is measured using bps (bits per second) or baud.


Private Vs Switched Channels

• Private leased lines are permanently connected circuits between two or more points.These lines are available for private use by the leasing party.

• Switched lines or dial up lines are available to any subscriber. For e.g. Telephone connection at our home or office


Analog and Digital Transmission

• An analog signal is one that is continuous with respect to time, and may take on any value within a given range of values. – Human voice, video and music when

converted to electrical signal using suitable devices produce analog signals.

• A digital signal may take on only a discrete set of values within a given range. Most computers and computer-related equipment are digital.


Parallel and Serial Transmission

• Parallel Data Transmission:- Multiple parallel lines connecting the transmitting and receiving units. Each wire carries a bit of information. Usually, one character id transferred in one go.

• Serial Data Transmission:- Each bit is sent sequentially one after another. It requires one pair of wire conductors receiving and transmitting units.


Communication Protocol/Standard

• Protocols are technical customs or guide lines that govern the exchange of signal transmission and reception between equipments.

• Some of the functions that communication protocol regulates are:

• Control of information transfer • Structure and formats of data • Error recoveries Re-transmission control • Interface managemen


DATA COMMUNICATION MODES

• Synchronous and Asynchronous Transmission

• Simplex, Half Duplex and Full duplex Communication


Synchronous and Asynchronous Transmission

• Synchronous Transmission:- characters are transmitted as groups with control character in the beginning and at the end of the bit train. The transmission and receiving intervals between each bit are precisely timed.

• Asynchronous Transmission:- Each Char is transmitted separately, one char at a time. Each char begin with a start bit (coding begin) and end with a stop bit (coding end). Then next character is sent, with start and stop bits.


Simplex, Half Duplex and Full Duplex Communication

• The direction in which information can flow over a transmission path is determined by the properties of both the transmitting and the receiving devices. There are three basic options:


Communication Hardware

• Sender and Receiver Hardware

• Communication Devices

• Communication Channel


• Sender and Receiver Hardware are used for handling Communication messages, data transfer etc.

• Nodes and Workstations

Data Communication is done using various communication devices and software inter-connected for information exchange. The devices used to communicate in a data communication network are called workstations. These workstations includes Computer, terminal, printer etc.

Sender and Receiver Hardware


• Multiplexer Multiplexing is a form of data transfer in which communication channels are used for several transmissions. Ex. Telephone lines.

In other words multiplexing is a type of network mechanism, which allows a number of simple, low cost terminals to share each communication line, introduces almost no delay and requires no special computer software.

Sender and Receiver Hardware


Communication DevicesModem or Modulation Demodulation• Computer generates digital data which is

unsuitable for long distances . Data must be converted to analog data is called modulation.

• The converted data in the form of analog signals can travel without any noise over long distances. This data when reaches its destination is converted back to digital data with the help of demodulation.

• Codec performs the opposite function of a modem


Communication Channels

• The most basic hardware required for communication is the media through which data is transferred .

• Two wires open line

• Twisted Pair Cable

• Coaxial Cable

• Fiber Optical Cables

• Wireless


Two wires open line

• This is the simplest of all the transmission media. It consists of a simple pair of metallic wires made of copper or sometimes aluminium of between 0.4 and 1 mm diameter, and each wire is insulated from the other.

• Distance: upto about 50 meters

• Data transfer rate: upto 19200 bits per second.


Twisted Pair Cable

• A twisted pair cable consists of pairs and copper wires. They are twisted together to enable canceling out noise and external disturbance to the signal that they carry.

• Distance: upto1km

• Data Transfer rate: upto 1-2 megabytes per second


Coaxial Cable

• Distance: upto 1km

• Data transfer rate: upto 100 megabytes per second

• A coaxial cable is of two types - a 75-ohm cable, which is used by the cable TV operators and the 50-ohm cable which is used in high-speed broadband networks and are low loss cables.


Fibre Optic Cables

• This contains a very thin (as thin as the human hair) cable made of optical fibre. The cable transmits much more data and much faster than others. This cable carries signals in light pulses. Telephone companies and large government organization which need and can afford it, are using it.

• Distance: long and medium transmission links

• Data transfer rate: upto 1000 megabytes per second


Wireless

• There will be no wires here and data will transmitted into radio waves, microwaves and through satellite channels.


A networking means connecting two or more computers together for sharing of information and resources.

A computer network is a collection of hardware and software that enables a group of computers to communicate. It provides shared resources includes data files, applications and hardware (printer) and other related resources.

Introduction to Networking


A networking is basically a communication system of computers. Just as the telephone system allows two people to talk to one another, networks allow computers to communicate.

The entire computer network can be classified into two Broad categories:-

1.LAN (Local Area Network)

2.WAN (Wide Area Network)


1. LAN :- A private network with in a range of 10 kilometers which is controlled by a single organization. It permits exchange of data and information among them with in a localized area. Typically it covers a building, a cluster of buildings.


LAN TopologiesA network Topology refers to the physical layout of the network in which all the devices are connected. The point of connection to the network by the station are called nodes.

There are several types of topologies

1. Star Topology

2. Bus Topology

3. Ring Topology


1. Start Topology:-

In this topology a number of stations are connected directly to a central station. The central controller manages and controls all communications between stations on the network.

Node

Node

Node Node

Node


2. Bus Topology:-

All the stations are connected to a single communication line. This single communication line is referred to as a bus.. On a Bus Network, all stations share the same medium.

Node

Node

Node

Node


3. Ring Topology:-

In this topology each station attached to an adjacent station using point-to-point link. Called a ring.

A

B

CD

E


LAN Access Method

Many techniques have been proposed, but two of these are commonly used

(i) Carrier-Sense Multiple Access with Collision Detection (CSMA/CD)

(ii) Token passing


Communication Architecture for Networking

Instead of using entire data communication as a single module, the task is broken into various subtasks. Each subtask operates separately by different layers of the communication architecture.

System that follow the OSI (Open System Interconnecting) are said to be open to one another at different layers and thus called open systems.

The easiest way design network is to break processes down into layers.


1. Physical Layer:- This layer defines the mechanical, electrical, functional and procedural standards for the physical transmission of data.

2. Data Link Layer:- It provides the functions and protocols to transfer data between network resource and to detect errors.

3. Network Layer:- This layer establishes connections between networks. It includes operational procedures for inter network communication.


4. Transport Layer:- This layer is responsible for transparent and reliable transfer of data.

5. Session Layer:- This layer provides the mechanism for organizing and structuring interaction between applications.

6. Application Layer:- This layer supports the applications of users and enables them to connect to the network.

7. Presentation Layer:- This layer presents data to the application layer.


The Basic Hardware components of LAN

1. Transmission Channel.

2. Network Interface Unit (NIU)

3. Server

4. Workstation

LAN Hardware & Software


Network Interface Unit

This unit connects each device in the LAN network to shared transmission device. It contains the rules or logic to access the LAN. NIU is also used to implement LAN protocols and for device attachments.


Server

A server is an important component of a network. The server runs the NOS and offers network services to users at their individual workstations. These services includes file storage, security, user management etc.

1. File Server:- is used to share storage space for files.

2. Printer Server:- Printer connected to the server can be accessed directly by all the users of the network.

3. Modem Server:- is also used to share telephone lines and modem by all connected workstations in a network.


Workstation:- When a computer is connected to a network. It becomes node on the network is called a workstation.

LAN Software:- Software of LAN OS facilitates the sharing of expensive resources such as printer, storage space etc. among all LAN users provides security for data.

Various types of LAN OS

Ex. Novel Netware, Windows NT


Communication Switching Techniques

• In a WAN, two computing devices are not connected directly.

• A network of switching nodes provides a transfer path between the two devices.

• The process of transferring data blocks from one node to another is called data switching.


• Circuit Switching

In circuit switching there is a dedicated communication path between the sending and receiving devices, like telephone network where a dedicated path is set between the caller and the called party for the duration of a telephone call is an example of Circuit Switching.

• Message Switching

In message Switching, the message is then passed through the network from one node to another till it reaches the intended destination. Example E-Mail, Telegrams


• Packet Switching

It combines the advantages of message and circuit switching. Same like Message Switching in which data is transmitted in blocks stored by the first switching node in the network and is forward to the next until it reaches its destination. Max length of packets is between 128 bytes to 4096 bytes.

• There are two approaches to packet switching

* Datagram

* Virtual circuit


WAN Devices/Hardware

• Bridges – Bridges are used to connect two LANs that use

identical LAN protocols over a wide area. – Bridges operate at the data link layer (layer 2) of the

OSI model. • Routers

– Routers can be used to connect networks that may not be similar.

– Routers operates at the network layer (layer 3).of the OSI model.

• Gateways – Gateways are used to connect two dissimilar LANs. – gateway operates on, the application layer (layer 7) of

the OSI model.


Types of Wide Area Networks

• Public Networks – Public Networks are those networks which are

installed and run by the telecommunication authorities and are made available to any organisation or individual who subscribe it.

– Public Switched Telephone Networks (PSTN)– Public Switched Data Networks (PSDN),– Value Added Services (VANs/VADs) and – the Integrated Services Digital Networks

(ISDN).

• Private Networks


Few Applications

E-Mail:-

E-Mail system is basically used for sending messages electronically to individuals or group of individuals in an inter or intra office environment. We can attach a file of any application software.


EDIEDI (Electronic Data Interchange):- It means replacing paper documents with electronic documents and replacing traditional methods of transmission such as Mail, Phone, in-person delivery with electronic transmission.

It can be used to electrically transmit documents such as purchase orders, invoice, shipping notice, receiving advices, transmit financial information and payments in electronic from.


InternetInternet is the world’s largest Network. It is a

global network. It is the best flower gifted by information technology.

Services:-

1. E-Mail

2. Usenet- Views and News:

Usenet is the BBS (Bulletin Board Service) of internet. The messages in this BBS are organized into thousand of News groups


3. Telnet (Remote Login)

Telnet allows an Internet user to access a remote computer (host). After properly connectivity and logging into the remote host, the user can enter data, run programs or do any other operations.

4. FTP (File Transfer Protocol):-

It permits an internet user to move a file from one computer to another. The files may have data, graphics, text etc.


5. Navigators (Information Servers)

There are several powerful tools used on internet for searching information. Means to develop easy method of discovering, locating, retrieving information from Gopher, WWW. WAIS (Wide Area Information Server)


Security:- Security means protection of data against accidental or intentional, destruction, discloser or modification.

Computer data security refers to the technological safeguards and managerial procedure which can be applied to computer Hardware, Software and data.


Privacy:-

Privacy applied to an individual. It is the right of an individual to decide what information he/she wishes to share with others.


Breaches of Security

1. Theft of PC

2. Damage due to breakage:- Floppies are easily breakable when we shifted from one place to another. Damage can also occur due to natural causes such as storm or flood due to electrical or other fires.

3. Environmental Damage:- Environmental conditions like temperature and humidity ranges, voltage limits, dust etc effects to PC and get damaged.


4. Inadvertent Corruption/loss:-

1. Usage of inferior media:- If sub standard media used, it would be cheaper, it may develop faults and data held.it may become unusable.

2. Erasure of files:- Files may be get erased from media due to incorrect actions by operator, wrong programming techniques, defective software.


5. Unauthorized Access

6. Modification Erasures:-The person accessing the data files may be authorized to read the data, modify or delete the data.

7. Environmental Losses

8. Malicious damage/leakage


9. Computer Viruses:-

This is the latest threat to computer users.

The problems created by viruses include:-

1. Destruction of File Allocation Table (FAT)

2. Erasing of specific programs or data on disc.

3. Destroy parts of programs/data held on disc by created bad sectors.

4. Overwriting of entire disc directories.

5. Hang the system at periodic intervals.


Security Measures

One of the best and first steps in ensuring data security is to create an awareness and develop a culture within the organization in which information can be lost/altered.

The other steps that can be taken are:-

1. IT Planning:- The organization must decide on a policy for introduction of IT. This must be done at highest level.

2. Selection of technology


3. Physical protection of machine.

4. Identification of points of exposure of weak links.

There are four Principles for ensuring Security and recovery in case of breaches of Security:-

1. Prevent

2. Detect

3. Minimize Damage

4. Recovery


Various Security Measures

1. Physical Security

1. Physically bolt down the PC

2. Floppies, Keyboards should be lock

3. Keep a record of all floppies in use.

4. Use lockable rooms for PC specially those handling sensitive data.

5. Locate the PC in such a way that it is conveniently accessible to the user but hidden from casual passerby.


2. Software Security

1 Use original software for operating system or software package.

2. Use Licensed software

3. Use correct procedure for shutting down the PC

4. Introduce password to access your applications. Password should not be visible on the screen

5. Keep backups of all your files.


3. Network Security

1. Keep the servers away and limit physical access to them for direct use of server.

2. Run servers in the background mode.For direct use, a separate password would be necessary.

3.Be aware that the network cables can be tapped, so that conceal them to prevent easy access, if possible, use fibre optical wire.

4. Use codes and ciphers in data communication.

5. Prohibit the use of passwords embedded in communication access script


4. Password Security

1. Identification:- User code indicates an object with a unique identify assigned to it.

2, Authentication:- This could be be achieved by asking some standard questions and getting answers to them. If answers match . The person is authentication.

3. Authorization:- Only a given user, terminal or other resource can access data to which permission has been granted to read, write or alter.A matrix can be created ti indicate which users have access to which file record. Otherwise he is denied.


CRYPTOGRAPHYCRYPTOGRAPHY is the process of transforming plain text or original information into an unintelligible form (cipher) text.

A data key control the transformation process.Authorized receiver

is assumed to have that key.

HELLO

XRVJF

Algorithm

(Encryption Process)

Plain Text XRVJF

HELLO

Algorithm

Decryption process Cipher

Text

Plain Text


Cipher Systems

These includes two classes are called

1. Transposition

2. Substitution

1. Transposition Cipher:- A transposition involves rearrangement or change in the sequence of the letters of the plain text, message.

2 Substitution Cipher involves a replacement of the plain text letter by other letters without any change in their sequence.


Code System:-

A code system is a specialized form of substitution in which entire words, long phrases or even sentences of the plain text are replaced by arbitrarily selected equivalents. These may be other words, groups of letters, groups of figures or some combination of these.

A code system makes use of a codebook in which the words, phrases and sentences of the vocabulary are listed in an organised manner and accompanied by their equivalent code groups.


DES (Data Encryption Standard)

IBM developed the DES algorithm. DES specifies a method for Encryption 64 bit blocks of plain text into corresponding 64 bit blocks of cipher text employing a user-specified 56-bit key.


VIRUS

Vital Information Resources Under Stress

Computer Virus are computer program which are a collection of coded information. The basic difference between a normal program and a Virus is that, virus are self replicating they have the capability of executing themselves without being asked for.

Viruses

Corrupt the most sensitive area of the disk the File Allocation Table (FAT)


The Process of Infection

The infection may begin as soon as a computer boots from a contaminated disk or executes an infected program. Whatever viruses are present gets activated which immediately begin to spread throughout the system.


Classification of Viruses

1. Boot Infectors: Infect the boot system

2. System Infectors:Infect the Hard disks

3. Executable Program Infectors:Infects the .EXE, .COM files.


Some Viruses

1. Score Virus:- activates two, four and seven days after the disk has become infected.

2. Brain Virus:- Pakistani Virus

3. Lehigh Virus:-with the booting of a PC from an infected disk then virus spread all the disk.

4. Friday the 13th: attacks not only the command.com but also attack other exe files.

5. Sunnyvale Slug: This Virus displaying a message ‘Greetings form Sunnyvale.


6. Raindrops:- This virus infects .com files. The first three bytes of the file are replaced by jumps instructions at the end of the file.

7. Happy Birthday 30th:


Prevention1. Use the CHKDSK

2. Don ‘t use pirated software on your system.

3. Write protect tags should be used on the original software disk.

4. Proper backup of all data and program files should be kept.

5. Copying of data files should be carefully

6. Restrict the use of outside floppies, Pen drives.


CureVirus can be cured by anti-virus program.

An ISO 9001:2000 Certified Organization CS-611 COMPUTER FUNDAMENTAL & PC SOFTWARE BCA-1 IGNOU.

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Transcript of An ISO 9001:2000 Certified Organization CS-611 COMPUTER FUNDAMENTAL & PC SOFTWARE BCA-1 IGNOU.