Friday, 25 May 2012

E-MAIL AND ITS ADVANTAGES


Email:-


Email stands for Electronic Mail. Email is the exchange of messages and files through Internet. Message can be in the form of graphics, sounds, video clips or simple text. it is a fast way of sending messages anywhere in the world in a very short time.
The sender and receiver may be sitting in the same building or anywhere in the world.
One email message can be sent to many people. Email facility is provided by many Internet
Service providers or specialized websites. Yahoo, Hotmail and Gmail are some poptilar.
examples of email providing websites.


Advantages and Uses of Email:-


Some advantages of email are as follows:
• It is very fast and timely.
• it is very cheap and inexpensive.
• People can send and receive message anywhere in the world.
• People can share information.
• It is possible to send and receive email through mobile phone.
• Email gives us the facility to send pictures, sounds and videos
• Email message does not disturb the recipient. It is stored on a server and can be read at any time.

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Thursday, 24 May 2012

Services Of Internet


Internet provides various facilities and uses for users. Some facilities are:


1. World Wide Web (WWW):-

www is a collection of millions of websites. A websites contains different web pages containing information. www organizes this information in such a way that users can easily search and access the required information.

2. E-mail:-

Email stands for Electronic Mail. Email is the exchange of messeges and files using Internet. Message can be in the form of graphics, sounds, video clips or simple text. It is a fast way of sending messages anywhere in the world in a very short time.

3.Telnet:-

TELNET is a program that is used to connecting a remote computer on Internet. A computer can act like a terminal directly linked to the computer. It allows a user to logon to a remote computer. The user can logon to the computer and use it as if he connected to the computer directly.
4. File Transfer Protocol:-
File Transfer Protocol is used to transfer files over the Internet. Audio, video, graphics and data files can be uploaded or downloaded using this protocol.
The process of transferring a file from remote computer to local computer is called downloading. The process of transferring a file from a local computer to remote computer is called uploading. Different software are available to use this protocol fo transferring files on the Internet. CuteFTP and WS_FTP are examples of FTP software.

5. Gopher:-

Gopher is a menu-based system for exploring the Internet and its resources. It provides the facilities of search and file retrieval on the Internet It organizes resources in such a way that finding information becomes easier on the internet.

6. Chat Groups:-

Chatting is a process of exchanging views on the Internet by typing text messages. Chat group is a group of users with similar interest. Many users join chat groups. The users can interact with one another in real-time. It means that they are online at the same time.

7. Intranet:-

Intranet is a private and secure business network. It uses Internet technology to provide information to the employees of the organization. The information can be protected from unauthorized users. It is designed to meet the internal needs for sharing information within a single organization or company

8.Extranet:-

Extranet is a collection of two or more intranets. It can be accessed by authorized users from outside the organization. Different organizations can use extranet to share the information of their intranets. An organization can apply security measures to provide limited access to the employees of other organization using the extranet.

Difference Between Intranet and Extranet:-


Intranet :-

1. Intranet contains the information of one organization.
2. Intranet is used to provide information to the employees.

Extranet :-

1. Extranet may have the information of two or more organizations.
2. Extranet is used to share information with other organizations.





Internet And Its History


Internet:-

Internet is a huge collection of computers all over the world that are all connected to one another. It is a global network of computers. These computers are connected through different telecommunications links like:

• Phone lines
• Fiber optics lines
• Satellites and wireless connections

Internet is used to find inf stored on the computers called hosts or servers. These computers use a common protocol called TCP/IP for communication. TCP/IP stands for Transmission Control Proto/Internet Protocol. Each computer connected to the Internet can act as host. A host c provides information to the people.
People can find informatfon about books, magazines, encyclopedia and other types of material on the Internet. -Th can get expert opinions on any topic. They can alsO communicate with world com’1 on different subjects. The Internet has made this world a global village.

History Of Internet:-

The work on Internet was started in 1960s during the cold war of Russia and America. America wanted to communicate with its Armed Forces. A network of four computers was developed in the beginning.
The project was handed over to DARPA (Defense Advanced Research Project Agency). DARPA started connecting computers at different universities and defense companies
Different universities and research organizations also started the development of their own networks to share inf√≥ and data with other people. After a few years, all networks of universities and research organizations were connected by DARPA with each other to make the world’s biggest network.This network is know known as Internet.
In 1989, all previous networks were replaced by NSFNET of National Science Foundation. The Internet facility was now available to common people.



Different access methods used by Ethernet to access a network


Different access methods used by Ethernet to access a network are as follows:

1. CSMA/CD:-

It is a local area access method. It resolves the contention between two or more stations by collision detection. If two sta) transmit data at the same time, they both stop and generate a signal that a collisionJ Each station waits for a specified time and then retransmits. Each stations waits for random period of time to avoid another collision.

2. CSMA/CS:-

In this method, a node listens to the bus for a specified time before transmitting. It waits until the node has completed the transmission.

3. CSMA/CR:-

It allows multiple devices to talk at the same time. A protocol is used to determine the priority of a device.

various lines for communication over telephone network


Different lines for communication over telephone network are as follows:

1.ISDN:-

ISDN stands for Integrated Services/digital Network. It is a set of standards for digital transmission of data over standard copper telephone lines. One telephone line can carry three or more signals at one time using the same line. ISDN requires ISDN modem at both sides. ISDN modem is different from dial-up modem.

2. DSL:-

DSL stands for digital subscriber line. It provides high-speed data transmission over existing telephone lines. The existing telephone lines are analog. That is why, DSL modem is required to connect to DSL. DSL is easier to install than ISDN and is also faster.

WHAT IS TCP IP


What Is TCP/IP?

TCP I IF stands for transmission control protocol I Internet protocol. It is the protocol used by every computer on Internet. A protocol is a set of rules and procedures that defines how computer receive and transmit data over the network.


• TCP/IP ensures reliable connection between different computers that communicate over Internet. It is used to identify every computer on the Internet separately.
TCP/IP software is different for different computers but provides same interface to the network. Two different types of computers can communicate with each other using this protocol. For example, a personal computer can exchange data with mainframe computer over the Internet by using TCP/IP.

Wednesday, 23 May 2012

Local Area Network Protocols


Network Protocol:-

Network Protocol or communication protocol is a set of rules for exchanging information between computers on a network.
Types of LAN Protocols:-
Different LAN protocols are as follows:

1. Ethernet

Ethernet is the most commonly used LAN protocol. It uses a high-speed network cable and bus topology. It is inexpensive and easy to install and. manage. All computers inEthemet tIse same cable to send and receive data. They must follpw same rules for communication. If- two or more computers transmit data at same time, the messages can be lost. A computer checks if the cable is in use before transmitting data. The computer waits if the cable is being used. It starts transmitting data when the cable is free. This process is also called CSMA/C$ (Carrier Sense Multiple Access with Collision Detection).

2. Token Ring

Token ring is also a LAN technology. It allows network devices to access the network by passmg a special signal called token Token is like a ticket A device can transmit data over the network only if it has a token. Only one token is available in one netwOrk is why no collision can occur. But the data transmission rate is slow. When a computer wants to send a message, it:
1. Gets the token
2. Puts the data in the token
3. Adds the address of receiving computer
Token ring is based on ring topology but can also be used in star topology. The token passes from computer to computer. The computer whose address matches with the address stored in the token gets the data. It then returns the message to the sending computer to indicate that the data has been received.

3. ARCnet


ARCnet stands for Attached Resource Computer Network. It is a LAN protocol. It was introduced in 1977. It uses twisted-pair, coaxial cable and fiber-optic media. ARCnet uses star, bus or combination of these topologies.
The original ARCnet protocol was very slow. It.supported transmission rates of 2.5 Mbps. It became popular because it was inexpensive and reliable. It isalso easy to setup and expand. Fast ARCnet increased the transmission rate to 100 Mbitspersecond.


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DIFFERENCE BETWEEN LAN AND WAN


DIFFERENCE BETWEEN LAN AND WAN:


LAN:-

1. LAN is used to connect computers at
one place.
2. LAN covers limited area.
3. Data transfer speed is very fast in LAN. Its speed is normally form 0.1 to 100 Mbps.
4. LAN is less costly.
5. LAN is usually connected through
wires.
6. The connection in a LAN is permanent
using wires.
7. LAN is used to share files and
hardware like printers, modem.
8. LAN has less possibility of data
transmission error.
9. In LAN, problems normally occur due
to cable disturbance by end user.


WAN:-

1. WAN is used to connect computers
anywhere in world.
2. WAN can cover more distance.
3. Data transfer speed is slow in WAN. Transmission rates are typically 56kbps to 45Mbps.
4. WAN is expensive.
5. WAN is usually connected through
telephone lines.
6. The connection in WAN is not
permanent.
7. WAN is used to share only data and
information i.e. email & file.
8. WAN has higher possibility of data
transmission error.
9. In WAN, problem normally occurs due to communication problems in medium.


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NETWORK TYPES OF COMPUTERS


LAN (Local Area Network):
Uses and Advantages of LAN:-
MAN (Metropolitan-Area Network): 
WAN (wide area network):
LAN is the most common type of network. LAN stands for Local Area Network. It covers a small area. Most LANs are used to connect computers in a single building, campus, office or room etc. Hundreds or thousands of computers may be connected through LAN. There are marty types of LANs. Ethernet is the most common for PCs.
The above figure shows a LAN. All computers are connected to a central node in star topology. The central node is a special device called a network hub. All links are made up of UTP cables. The maximum recommended length of a UTP connection in LAN is 100 meters. No computer should be more than 100 meters away from hub.
All computers in LAN can communicate with each other at a high speed. The speed of communications between any two devices on an Ethernet LAN can be 2 to 1000 millions bits per second (Mbps). LAN can transmit data in a limited distance.

• One copy of a software can be shared by all users in a LAN
• System resources such as printers can be shared between several people in network.
• It is easy to manage the data stored on a centralized computer in the network.
• The data is more secure from being copied or destroyed.
• Data can be shared by all users using the network.


A metropolitan area network (MAN) is a communications network that covers a geographical area of the size of a city. A MAN typically include one or more LANs but cover a small geographical area than WAN. A MAN often acts as a high-speed network. Mobile phones systems often use MAN.




WAN stands for wide area network. It refers to a network that covers a large area. WAN connects computers in different cities and countries. Computers in WAN are often connected through telephone lines. They can also be connected through leased lines or satellites. WAN can reach the parts of the world that is not possible with LANs.
The mainframe and- minicomputers used in WAN are designed to be accessed by terminals. A personal computer must appear as a terminal to communicate with large computers in WAN. Tetminai emulation software is usedlo allow a personal computer to appearas In this-way the personal computer can connect to a large computer.
The larger computer is known as host computer. A personal computer attached to host computer can upload and download data. The transfer of data from personal computer to host computer is known as uploading. The transfer of data from host computer to personal computer is known as downloading. File transfer soffware is used to do upload and download data.
Transmission rate of WAN is typically 56kbps to 45Mbps. WAN is not as fast as LAN.
It requires long cable distances and there is a possibility of error in data transmission.




Tuesday, 22 May 2012

Different Networks Models.


There are two models of computer networks. These are as follows:


  • Client-Server Model.
  • Peer-to-Peer Model.

1. Client-Server Model (Dedicated Server Network):

In client-server model, one or more computers work as servers nd other computers work as clients. The server computer controls the whole network. It is used to store data and programs to be shared among different computers in the network. It may also share a printer attached with it. Server is more powerful computer than other computers in the network. It performs most of the processing in this network model.
The client computer requests a service from the server computer. The server computer provides the requested service to the client computer.
Some servers are called dedicated servers. A dedicated server is used to perform a specific task. For example, file server is used to store and manage files. A print server is used to manage printers and printing tasks. Similarly, network server manages network resources.


Advantages:-

Some important advantages of client-server model are as follows:
• It reduces the volume of data traffic on the network.
• It also provides faster responses to the clients.
• It can use less powerful computers as clients because most of the-processing is done by the server computer.

Disadvantages:-

• It is expensive model because server computers are costly.
• The operations stop all over the network when server goes down.

2. Peer-to-Peer Model:

All computers in peer-to-peer model have same status. There is no server computer to control other computers Each computer in this network can have access to the devices and files on the other computers Each computer independently store its own software and information.

Advantages:-

Some important advantages of peer-to-peer model are as follows:
• It is easy to setup:
• It is easy to maintain.
• It does not require expensive server computer.
•. It is suitable for sinalloffice of ten or less computers.

Disadvantage:-

The main disadvantage of this model are as follows:
• Heavy use can slow down the network speed:
• It also provides less security of data because files are stored at different locations in the network.



Hybrid Model:-

Hybrid model is a combination of client/server model and peer-to-peer model. Many networks use a mixture of both network models. This model can provide the advantages of both models.




TYPES OF COMPUTERS IN A NETWORK


Terminal Computer:-

Every computer that is part of a computer network is called a terminal or node. The users using different terminal computers can share information and send or receive data from one terminal to another.

Server Computer:-

A server computer in a computer network is used as a central computer. It contros other computers in the network. Server computer is more powerful than terminals.

Sunday, 20 May 2012

BASIC COMPONENTS OF COMPUTER SYSTEM

BASIC COMPONENTS:

There are four basic components of a computer system which are explained below.
  1. Input Devices
  2. Processing Devices
  3. Output Devices
  4. Storage devices
  • INPUT  DEVICES:

The data that is given to computer system is called input. Input devices are used to input data and instructions to a computer. These devices send  this data to processing unit.most commonly used input devices are mouse and keyboard.
  • PROCESSING  DEVICES:
The processor is used to process data.it is also called central processing unit(CPU). It is the Brain of the Computer. It consists of electronic circuits. CPU interprets and executes program instruction. All computers must have a central processing unit.
Main memory is used to store the input data before processing. It also stores processed data after processing until the data is sent to the output device. The main memory is closely connected to CPU but is separate from it.
  • OUTPUT  DEVICES:
The data processed into useful information is called output. Output devices are used to display the result of processing. The most common output devices are monitor and printer.
  • STORAGE  DEVICES:
Storage usually refers to secondary storage. The main memory stores data and programs temporarily . The secondary storage is required to store data,information and programs permanently. The most common storage floppy disk,hard disk drive and CD-ROM etc......