RIng topology

Ring topology:

In this topology, each node is connected to two and only two neighboring nodes and forms, a close loop, • It is fast, short cabling and reliable but break in loop affects all devices on network, difficult to configure and troubleshoot.

b) Bus Topology:

b) Bus Topology:

It consists of a single length of transmission medium(normally coaxial cable) onto which various nodes are attached i.e. it provides a common or shared communication pathway, It is easy to install. extend, needs short cabling, low cost but difficult to troubleshoot and less reliable.

LAN Topology:

LAN Topology:-

The pattern of interconnection of nodes or workstations in a network is termed as a network topology, Before selecting a topology one should consider on the factors such as cost, flexibility and reliability of the topology. Some common LAN topologies are:

a) Star Topology:

It consists of a central hub to which all other nodes are connected by a single path. The advantage of the star topology is that every connection is dedicated to one user so it gets full bandwidth of the channel, easy to troubleshoot and simple access protocol. Its disadvantage is high cost of media and equipment needed to supply individual connection and central node dependency,

Types of Network

Types of Network:-

The computer networks vary in size, complexity and geographical spread. Mostly on the basis of a geographical spread, there are three basic types of networks, which are:
1. Local Area Network (LAN)
2. Metropolitan Area Network (MAN)
3. Wide Area Network (WAN)
Local Area Network (LAN): It is a small computer network that is confined to a localized area, such as a building, an office or a factory. LANs are found in most business enterprise, government offices, and educational institutions. The key purpose of a LAN is to serve its users in sharing data, information, programs, printer, hard disk, modem, etc. In this network, computers are mostly connected with a physical medium such as a twisted pair cable or coaxial cable.

Network Architecture

Network Architecture

Depending upon the involvement/contribution of computers in a network system, there are two types of network architecture which are, client/server architecture and peer to peer architecture,
Client/Server Architecture
A network architecture in which each computer or a process on the network is either a client or a server, Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers). Clients are PCs or workstations on which users run applications. Clients rely on servers for resources, such as files, devices, and even processing power,
Peer-To-Peer Architecture
It is often referred to simply as peer-to-peer, or abbreviated P2P. It is a type of network in which each workstation has equivalent capabilities and responsibilities. Unlike the client/server architectures, in which some computers are dedicated to serving the others, in this architecture, each node (a computer in network) may have equal contribution to the system and available system resources can be shared among them.

Network Hardware

Network Hardware:

Network hardware directs the flow of data over the network channels.

Network Interface Card (NIC): It is a network adapter, a small circuit board designed to plug into an expansion slot on a computer motherboard, It accesses the physical media that link computers, receive packets from the network software, and transmits instructions and requests to other computers.

Network Hub: It is a device that joins communication lines together. There are two types of hubs viz, passive hub (which add nothing to the transmission) and an active hub (which may regenerate signals to boost strength as well as monitor activity).

Repeater: A device that amplifies or regenerates the data signals in order to extend the distance of a transmission.

Router: A device that examines the destination address of a message and selects the most effective route. It is used in complex networks where there are many pathways between users.

Bridge: A device that connects two networks of the same type together, a contrast with a gateway.

Gateway: A computer that inter-connects and performs the protocol conversion between two dissimilar types of networks, contrast with a bridge.

MODEM: A modulator and demodulator, a communication device that converts digital signals to A/F (audio frequency) tones, which are in the frequency range that the telephone lines can transmit and also convert the transmitted tones back to digital signals.ATM : Automated Teller Machine, a special purpose device with a keypad and display unit, connected to bank's computer in order to serve the remote financial transaction.

Communication Channel

Communication Channel

The media through which the communication is established or the workstations are interconnected is called communication channel. A network may use a physical medium such as cables and optical fibers or/and wireless medium such as radio wave or micro wave for communication. The transmission capacity of a communication channel is termed as Bandwidth,
The most commonly used communication channels are:

Twisted-pair cable: It is just like a telephone cable, which consists of copper wires twisted together and terminates in a square plastic RJ-11 or RJ-45 plug or connector.

Coaxial cable:It is like cable-TV or cable with a round, silver BNC connecter at either end and is a high-capacity communication cable consisting of a copper wire conductor, non- conducting insulator, metal shield (net), and plastic outer coating.

Fiber-optic cable: It consists of a bundle of extremely thin tube of glass. Each tube, called an optical fiber, is much thinner than a human hair. It usually consists of a strong inner support wire; multiple strands of optical fiber, each covered by a plastic insulator and a tough outer covering.

Network Software

Network Software

A network software or network operating system (NOS) is a type of software that manages network resources, controls the flow of data, maintains security, and tracks user accounts. It consists of computer programs that establish protocols, or rules, for computers to talk to one another. These protocols are carried out by sending and receiving formatted instructions of data called packets, Protocols make logical connections between the computers in a network, transfer packets from one computer to another, and minimize the possibility of collisions between packets sent at the same time, Some popular network operating systems (NOSs) are;
Novel NetWare, Windows 95/98, NT Workstation and 2000 Professional,

Common Symptoms of Infection

Common Symptoms of Infection

# Your program takes a longer time to load suddenly.

# The program size keeps changing,

# Your disk keeps running out of free space.

# You keep getting 32 bit errors in Windows.

# The drive light keeps flashing when you are not doing anything.

# You may notice a list of unnecessary files with a strange
filename, which you have never created and used by your system.

# Clicking noise keeps coming from your keyboard. D Your computer may not remember CMOS settings even though
the battery is new. etc.
Preventive measures
# Keep 'Write Protect' tabs on all your system disks. If possible.

# available, go for virus protection software.

# Do not use pirated software,

# Do not accept free software that looks too good to be true,

#Buy software only from proven source.

# Do not use external Floppy disks, if possible.

# Avoid swapping floppies across machines.

# Avoid booting from many floppies, in case your system does not
have a hard disk.

# Check all floppy disks periodically and remove infected programs

Common Routes for virus infiltration

Common Routes for virus infiltration

# Floppy disks or other media that users can exchange.

# E-mail attachments,

# Pirated software.

# Shareware.

How Do Computer Viruses Spread?

How Do Computer Viruses Spread?

Infections spread from machine to machine, and from organization to organization, in a number of ways. Basically viruses can be transmitted by:

# Booting a PC from an infected medium.

# Executing an infected program,

# Opening an infected file,

Types of Computer Virus

Types of Computer Virus

Viruses may be classified under four major categories according to their nature and the way they infect a computer system.

1. Message Carrying Viruses:
These viruses do not infect the computer programs and do not damage data and information but display (pops up) interesting messages, pictures, dialogues, etc. which may entertain the computer user.
2. Boot Sector Viruses:
These viruses infect diskettes and hard disks and become active when an infected disk is used to start the computer. These viruses infect Boot Record, Master Boot, FAT and Partition Table,
3. System Infectors:
System infectors infect/destroy/corrupt the system files concerned with OS such as IO.SYS, MSDOS.SYS, COMMAND>COM, etc. These enter to the system as a device driver and get loaded into memory,
4. Application Infectors or Program Viruses:
These viruses infect computer programs (executable program files such as .COM, .EXE, OVL, .DRV, SYS, .BIN, etc.) and become active when the infected program is run,
Nowadays, some new category of viruses is also found which can be classified as:
a) Multipartite Viruses: These viruses show multiple features which can infect both programs and boot sectors.
b) Document Viruses or Macro Viruses: These viruses infect MS Word documents (files) through the macro programming capabilities of some newer programs. Macro virus becomes active when an infected document is opened, and the program opening the document has its macro capabilities turned on (enabled).

Computer Virus

Computer Virus

Computer virus is a parasitic program written intentionally to enter a computer without the user's permission or knowledge. The word parasitic is used because a virus is attached to files or boot sectors and is replicated itself thus continuing to spread. Though some viruses do a little damage but replicate, others can cause serious damage or affect a program and system performance.
Basically, a computer virus is a special kind of computer program, which spreads across disks and networks by making copies of itself, usually secretly and can produce undesired side-effects in computers in which it is active,

Software Security

Software Security

Software security refers to the protection of computers' software resources from being pirated, deleted, corrupted, infected from viruses, etc. The failure in computer software security may cause the malfunctioning of a system, breaking secrecy of confidential resources, loss of large amount of data, waste of man power, etc.
Software Security Measures
1. Operating system / network system with adequate automatic protection capabilities and system security measures should be used.
2. Operating system and application programs should be virus free and safety measures to stop virus infiltration should be adopted,
3. Users should be very aware of the entry of wrong commands.
4. Password-should'be used to avoid accessing by unauthorized users. The password should also be changed frequently.
5. Essential files should be encryp+ed (converted into codes).
6. Data input must be authorized and monitored.
7. Access privileges should be closely monitored.
8. Data should be validated before it is processed.
9. Backup copies of data and software should be kept, etc.

Hardware Security

Hardware Security

Hardware security refers to the protection of computers' hardware resources from physical loss or damage.
Hardware Security Measures
1. Computers should be kept in an appropriate temperature i.e. the room temperature should be maintained in between 18 to 24 degree Celsius for older system and between 0 to 40° C for modern systems otherwise the system may cease to work.
2. We should maintain an appropriate power supply system. Computers need 220V to 240V constantly and the frequency of electric current could be ranged from 49.5 to 50 Hz, It is recommended to use power protection devices such as Volt Guard, Spike Guard, Stabilizer, UPS system etc.
3. The computers' room should be clean, bright dust/smoke-free, dry, well ventilated and air-conditioned.
4. Computers should be checked regularly and servicing should be followed periodically, They should not be kept packed for a long time.
5. Unnecessary persons should not be allowed to operate the computers.
6. The computer room should be well locked, grilled, etc,

Hardware Security

Hardware Security
Hardware security refers to the protection of computers' hardware resources from physical loss or damage.
Hardware Security Measures
1. Computers should be kept in an appropriate temperature i.e. the room temperature should be maintained in between 18 to 24 degree Celsius for older system and between 0 to 40° C for modern systems otherwise the system may cease to work.
2. We should maintain an appropriate power supply system. Computers need 220V to 240V constantly and the frequency of electric current could be ranged from 49.5 to 50 Hz, It is recommended to use power protection devices such as Volt Guard, Spike Guard, Stabilizer, UPS system etc.
3. The computers' room should be clean, bright dust/smoke-free, dry, well ventilated and air-conditioned.
4. Computers should be checked regularly and servicing should be followed periodically, They should not be kept packed for a long time.
5. Unnecessary persons should not be allowed to operate the computers.
6. The computer room should be well locked, grilled, etc,

COMPUTER SECURITY

COMPUTER SECURITY

Computer security refers to the protection of the computer's resources from accidental, intentional or natural disasters, including theft, physical damage, heat power management illegal access, data piracy, virus infection, etc,
Computer security can be studied under two major categories:

1. Hardware security

2. Software security

Business Communication

Business Communication

Multimedia is a very powerful tool for enhancing the quality of business communications. The business communications such as employee related communications product promotions, customer information and reports for investors can be presented in multimedia form.
On the Internet
One of the areas where multimedia is used extensively is the Internet. There are many web sites where we can find information presented using different media such as text, graphics, animations and video clips which make those web sites more comprehensive.

Edutainment

Edutainment is nothing but educational entertainment. Many computer games with focus on education are now available. A simple example, in this case, is an educational game that plays various rhymes for little kids. In addition to playing rhymes, the child can paint the pictures, increase or reduce sizes of various objects, etc. Similarly, many other edutainment packages which provide a lot of detailed information to kids are available. Microsoft has produced many such CD-based multimedia such as Sierra, Knowledge Adventure, etc. that in addition to play, provide some sort of learning components. The latest in this series is a package that teaches about the computer using games playing,

Entertainment

Entertainment

The entertainment industry has used this technology the most to create real life like games, Several developers have used graphics, sound, animation of multimedia to create variety of games. The special technologies such as virtual reality have made games just like experiences of re simulator that creates a real-life.
Many multimedia games are example; you can drive cars or any musical instrument, play different game, etc.

Sound Card

Sound Card

The most common reason for adding a sound card to a PC is to be able to use multimedia fully by recording and playing back the digital audio. While selecting an add on a sound card, the quality of sound from the loudspeaker has to be taken into consideration and the software provided with a sound card should be adequate enough to suit your requirements for handling sound effects in a multimedia.
While installing a sound card, one should keep in mind that it should not conflict with any other external devices installed in the computer system. Installation of a sound card might require some default settings to be changed to make it compatible with the computer system,

CD-ROM

CD-ROM

A CD-ROM is a very important storage device that has become an essential component of a multimedia computer because of its mass storage capacity and portability, A CD-ROM drive is a common hardware component of a multimedia computer. A scanner can also be used along with a multimedia PC for scanning the pictures and putting them in digitized form in the computer,

The Monitor

The Monitor

The multimedia PC should be equipped with a monitor having super Video Graphics Array (SVGA) card. The basic advantage of having SVGA is that it has a better resolution, thus, the display will be of better quality for the graphics and pictures. A typical representation which may be used in multimedia can be 720'640 or 1200'680 etc.

The CPU

The CPU

The CPU, which is recommended for a multimedia computer, should be Pentium processor on a PC or other advanced chips such as PowerPC, etc. Apple Macintosh and Silicon graphics have their own set of powerful processors for a multimedia, However, the CPU of a multimedia computer should beJit least 486 with math co­processor attached otherwise the response time of multimedia will be poor. The co-processor chip greatly reduces the load of the CPU, The powerful co­processor chip added for supporting graphics is called graphics accelerator,

Software

Software
Software comprises the instructions that tell the computer what to do. In general, a software is classified into application software and system software.-

Application Software is software that has been developed to solve a particular problem, to perform useful work on specific tasks, or to provide entertainment, Application software may be custom tailored or packaged. This may be thought as a kind of software that people use to perform a specific task, such as word processing software used to prepare documents and game software used to entertain the users.

System Software, which includes operating systems, enables the applications software to run on the computer. This may be thought as the underlying software that the computer uses to manage its own internal activities and run applications software. A system software acts as the interpreter that allows you and your application software to access the physical hardware devices and other resources, You must have a system software, otherwise you will not even be able to "boot up" (start) your computer.

Hardware

Hardware

Hardware consists of all the machinery and equipment in a computer system. It includes the keyboard, the monitor, the printer and the computer or processing device itself.

In general computer hardware is categorized according to the operations it performs:
Devices that are connected to the main computer cabinet are referred to as peripheral devices. A peripheral device is any piece of hardware that is connected to a computer. The examples are the keyboard, the mouse, the monitor and printer. An input hardware consists of devices that allow people to put data into the computer in a form that a computer can use, For example, an input may be by means of a keyboard, mouse, microphone, or scanner.

The system unit, or system cabinet, houses the electronic circuitry called the CPU (Central Processing Unit), which performs actual processing and main memory supports processing. The CPU is the computing part of the computer. It controls and manipulates data to produce information, In a personal computer, the CPU is usually a single, fingernail size chip called microprocessor, with electronic circuits printed on it. This microprocessor and other components necessary to make it work are mounted on a main circuit board called a motherboard.

Memory also known as main memory, RAM (Random Access Memory) or primary storage is a working storage. Memory is the computer's workspace, where data and programs for immediate processing are held. Computer memory is-contained on memory chips mounted on the motherboard. Memory capacity is important because it determines how much data can be processed at a time.

Output hardware consists of devices that translate the information processed by the computer into a form that humans can understand. As a personal computer user, you will be dealing with three principal types of output hardware - monitors, printers and other output devices. The monitor is the display unit of a computer. A printer is a device that converts computer output into printed images. Sound processors and speakers can produce digital music or human-like speech.

Secondary Storage hardware consists of devices that store data and programs permanently on a disk, tape or other media,
Media refers to the material that stores data such as a disk or, magnetic tape. For microcomputer, the principal storage media are diskette (floppy disk), hard disk, magnetic tape and CD-ROM.

Data / Information:

Data / Information:

# Data can be considered as raw materials - whether in, paper,
Electronic or other forms. Data consist of raw facts and figures
that is processed into information.

# Information is the summarized raw data of students' marks scored in different subjects are processed by a computer into information of mark-sheet. Some characteristics of useful information are that they are relevant, timely, accurate, concise, and complete,

Procedure

Procedure

A procedure refers to the description of as to how things are done - steps for accomplishing a result or rules and guidelines for what is accepted. Procedures are provided in manuals. Manuals, called documentation, contain instructions, rules, guidelines to follow when using or hardware and software.

People

People

People are the most important part of a computer and communication system. Two types of people use information technology - computer professionals, and end-users.
A Computer Professional, or an information technology professional, is a person who has an extensive or a considerable experience in the technical aspects of using a computer and communication system, For example, a computer programmer creates the programs (software) that process the data in a computer system,
An End-User or simply a user is some one with moderate technical knowledge of information technology who uses computer for entertainment, education, or work-related tasks. For example a person who does not know exactly how the Internet works but who knows how to use it.

INTRODUCTION AND EVOLUTION OF COMPUTER

introduction:
Computer is the most powerful device that man has ever made. It has made a great impact on our everyday life. Consider this statement "everything is in computer". Does it sound like an overstatement? No! This statement is true. Nowadays, everything is in computer means any information you can gel easily with the help of computer and its technologies. That's why "Everything is in computer" and as a result "computers are everywhere".
In the past three decades, technology has been transferred from developed countries (Britain, USA) to the Nepal as well. As a result, most of the citizens of Nepal have been using the computers these days. We use computer because of its influence in professional endeavors for daily life. With the invent of computers, all sciences, accounting, financial, cultural, art, historical, medical, engineering and current other disciplines are required to change with the base of computer or computing environment. No disciplines shall survive for long time until they would base their studies through computer. We used to say 'Mathematics is a god of science". In the same context, computing has been recognized as "brain for all kinds of operational area".
Six decades ago our past generation was referred as illiterate as they were not capable of writing a letter to (heir children and their dears. In addition to this, these days the people would be treated as illiterate because of incapability to send message through e-mail. Nowadays, computing environment is really very interactive and has reduced distance to a lot. Now, the world has turned into a global village due to computer and information superhighway. So, we can get information easily at any part of the earth within a minute.