There are three major possible ways of networking such as the LAN, WAN and MAN. Since the 1980’s LAN has gained prominence and is most commonly used. A LAN is a group of desktop computers located relatively close to each other and connected through cabling system to enable them to share access to computing resource. LAN satisfies two requirements namely sharing information and sharing computer resources. A LAN consists of PC’s on the same floor of a building or situated on different floors on the same building. It may even consist of computers which are within the factory area, but spread across various buildings like administrative block or production block or warehouse, etc. LAN consists of workstations which are connected to a central computer called file server. All workstations on LAN would have a network interface. There are various topologies available based on how the systems are connected namely the star, bus and ring topology.

Mainframe computers are expensive, large centralized computer facilities where a super computer is connected to a number of terminals. A multi user mainframe computer has a large memory and is capable of speeds of the order of several billions of floating point operations per second. Mini computers are also multi user computers operating at comparatively slower speeds and lesser memory. In the mini computers some popular versions are PDP-11, DEC10 ,etc. Micro computers  are often called as personal computers and they are based on micro processors manufactured by Intel, Motorola ,etc. These were designed for use in office or home. The home computer provides education, entertainment, information and communication facility in homes. One can send e-mails, e-greetings, chat, play games, hear music, video conferencing, reserve tickets, do shopping and banking operations with the help of a home PC and internet without leaving one’s home. Office based PC’s on the other hand are used to carry out many other functions like maintaining databases and doing calculations.

The first four generations of computers were based on the technology of the age to which they belonged. They were thus based on the vacuum tube technology, the transistor and printed circuit technology, the integrated circuit technology and the Very Large Scale Integrated (VLSI)technology. The major feature of the fourth generation technology is that a microchip weighing a few grams that is a thin silicon chip using 0.13 micron technology has a memory capacity if one gigabyte. At present, development has entered areas of “Artificial Intelligence”. These are called fifth generation computers. Today computer classification is based on various other parameters such as the microprocessor used, the speed , the motherboard configuration and many other factors. The latest computers are classified as mainframe computers, mini computers and micro computers. Each of these have their own features which make them advantageous to use in different fields of their own. The major features are discussed.