First computer were built in the era of second world war, and those are most expensive and isolated. Although, after twenty years prices is gradually decreased. It is used to allow several hosts to transfer information between them through. To permit any host send message to any other host in network, the simplest solution is to arrange them as a full-mesh, with end-to-end and loyal link between each and every pair of hosts.
Computer network oftenly classified on geographical area which they cover:
LAN: It is a local area network, which typically interconnects hosts, which are up to a some or may be tens of kilometer apart. This network is privately owned in office. It is very popular at these place, such as, Home, cafeteria, old buildings.
MAN: It is a metropolitan area network, which typically interconnects devices, which are up to a few hundreds of kilometer apart. Most common examples of MAN's is cable television network, it is not only example of MAN, another development of MAN is high speed wireless Internet access called WiMAX.
WAN: It is a Wide area network, which are cover all over the world or anywhere on the earth. In this system, networks are connected to their hosts, known as communication subnet or subnet. The work of subnet is carry all informations one to another host, for an example telephone system.
It is basically divided into two parts: 1)Peer-to-peer network, 2)Client-server network
Peer-To-Peer Network: It is executed, where less than ten computers are worked and where strict security is not required. Word 'Peer' is given because each computers have same network status, and they communicate with each other on same platform. Category of files, like word files or spreadsheet processing, can be serving over the network and each computer on the network can attached devices like printers, scanners, which are connected to any one computers.
Client-server network: It is more acceptable for wider networks. A central server works as the storage location for files and applications which shared with network. Generally, the server is higher than average performance computer. And also server controls the network access of the other computers which are mentioned as a 'client' computers. Typically, will use the client computers for their work and only the network administrator will have access rights to the server.