Tuesday, June 23, 2009


A Modem (short for modulator-demodulator) is a computer peripheral that allows your computer to connect to, and communicate with, other computer via telephone lines. This device converts the digital signal produced by the computer into analogue signals. These analogue signals are sent along a telephone lines to another modem, where they can are converted back into digital signal for the receiving computer. Anything that can be stored on a computer can be sent to another computer when connected by a modem and a phone line.

There are two types of modems available, namely: Internal and external modems.

Internal modem: An internal modem is fixed into an expansion slot located on the computer main board or it may be part of the computer main board (then known as integrated modem).

External modem: It is a separate unit, and connects to the computer via a cable. Five or six small lights on the top, or in front of the modem case, indicates the status of the modem and that of the data it is sending or receiving.

Advantage and Disadvantage of Networking.


1. Expensive peripherals devices such as laser printers and scanners can be shared between users.

2. Messages can be sent between users using LANs or WANs.

3. All users can access the same files.

4. It is possible to access data or programs from any terminal/workstation.

5. Data and software can be stored centrally, which makes them easier to maintain and back up.


1. If a WAN is used, sophisticated (complicated) equipment is needed and the rental of telecommunication links makes it very expensive.

2. File security is more important with networks. For instance, if a virus were to get onto network then it could effect all the network terminals.

3. Wiring can be expensive both to buy and to install.

4. In a type of network called a file-server network all the programs and data is stored on a main computer called a server. If the server breaks down, the whole network become unusable.

5. Networks are unpredictable; they need an experienced person to keep them running successfully.

Hierarchical networks

Hierarchical networks are those networks where one or more computers are more powerful than the rest. Hierarchical networks are often called client-server networks because a more powerful computer called the server is used to look after printing, file maintenance and other peripherals. There are two types of server: the print server and the file server.

The file server is a computer used for managing the files on a network. It is used to store both programs and data and is generally more powerful computer than the others to which it is connected. A print server is the name given to a computer in a network which has a printer connected. This server manages all the print requests from users on the network.

Star Topology

In the star topology, there is a computer at the centre that is used to control the whole of the network. If centre machine break down, then the whole network breaks down. Star topologies use more cabling and therefore more expensive than other topologies. There is a path from each terminal to the central computer; this type of topology is very fast.