Minicomputers
These are systems designed for multi-user access from several terminals. Varies from processing power from a very powerful micro to a small mainframe. Minicomputers are fast computers that have greater data manipulating capabilities than personal computers and can be used simultaneously by many people. These machines are primarily used by larger businesses to handle extensive accounting, billing, and inventory records.

Mainframes
Supports hundreds of terminals for multi-user access. Large amount of primary and auxiliary storage. Mainframes are large, extremely fast, multi-user computers that often contain complex arrays of processors, each designed to perform a specific function. Because they can handle huge databases, can simultaneously accommodate scores of users, and can perform complex mathematical operations, they are the mainstay of industry, research, and university computing centers.

Supercomputers
These are the fastest and most expensive systems. Although they are not multi-user machines, they are used when a vast amount of processing is to be done. The speed and power of supercomputers, the fastest class of computer, are almost beyond human comprehension, and their capabilities are continually being improved. The most sophisticated of these machines can perform nearly 32 billion calculations per second, can store a billion characters in memory at one time, and can do in one hour what a desktop computer would take 40 years to do. Supercomputers attain these speeds through the use of several advanced engineering techniques. For example, critical circuitry is super cooled to nearly absolute zero so that electrons can move at nearly the speed of light, and many processors are linked in such a way that they can all work on a single problem simultaneously. Because these computers can cost millions of dollars, they are used primarily by government agencies and large research centers.

Networks
Computers can communicate with other computers through a network to exchange data and share software and hardware resources.
Local area network (LAN)
consists of several PCs or workstations connected to a special computer called the server. The server stores and manages programs and data. Mainframe computers and supercomputers are usually connected to PCs, workstations, or "dumb" terminals used only to enter data into, or receive output from, the central computer.
Wide area networks (WANs)
Computers can connect to these networks to use facilities in another city or country. The largest WAN is the Internet.
Computers are more often also being equipped with a modem for connecting to the Internet and 'surfing' the WWW. The WWW is a system of information accessed through the Internet.