Kind of computer

Computers vary widely in size, speed, and ability. They may be grouped into four categories: (1) personal computers, (2) mainframes, (3) dedicated computers, and (4) embedded computers.
(1) Personal computers are used by one person at a time. The largest personal computers, or PC's, can fit on a desktop. Some of these machines have more than one microprocessor. Besides the primary processor, which is a general-purpose device, a PC may have one or more co-processors to handle special kinds of work. Some machines, for example, have math co-processors. Others have graphics co-processors to help process photographs and other illustrations. Still others have sound co-processors.
Large and middle-sized businesses commonly use PC's in client-server networks. A network consists of a group of computers connected by telephone lines or other communications cables. In a client-server network, a powerful central computer distributes information to a number of PC's. The central computer is called the server. The PC's are the clients but are usually referred to as workstations or simply PC's. The central computer may be a PC, a machine much like a PC with extra-large storage capacity, or an even larger type of computer.
The server also stores the entire network's essential information. In a typical network, individuals operating the workstations obtain copies of information from the server. The workers process this information, and then send copies of the processed information back to the server. In most cases, the workers are in the same office as the server. But a large company may have a network that connects its branch offices to the main office. In addition, many employees work on computers at home and send their processed data to the company server. This use of computers is known as telecommuting.
Small, portable PC's are popular with people who often work away from their desks. The portables include laptop computers, which can be held on the lap; notebook computers, which are about the size of a loose-leaf notebook; and palmtop, or handheld, computers, which can be operated while held in the hand. Laptop and notebook computers have the same power as desktop computers. Palmtop computers have less power but still provide some advanced computing capabilities. For example, they can process household financial data.
(2) Mainframes are the fastest computers, and they use the largest storage systems. As a result, they can solve more complex problems and handle more information than can any other category of computer. Mainframes are also the largest computers. Most of them are housed in several large cabinets. The fastest mainframes are called supercomputers. These machines are used for major projects, such as the design of aircraft, the study of weather systems, and the design and analysis of drug molecules. Supercomputers are few in number because they are extremely expensive. Supercomputer users, mostly scientists and engineers at large scientific installations, sometimes run programs by means of long-distance telephone networks.
(3) Dedicated computers are special-purpose machines. They include video game units and word processors. Video game units come in a range of sizes. The smallest are handheld, battery-operated toys. A larger unit for home use sits on the floor or a table and is connected to a television set. A player controls some of these home units through a lever called a joystick. The largest units stand on the floor in game rooms called arcades and other commercial establishments. Word processors are computers that mainly type, edit, and print letters and other documents. Some of them can also run simple financial programs. Many word processors resemble electronic typewriters, with a small screen built in above the keyboard. Word processors are much less expensive than PC's.
(4) Embedded computers are control units that are built into the devices they control. Virtually all embedded computers are single microprocessors. Such devices as digital wristwatches, telephones, videotape recorders, and the ignition systems of automobiles contain embedded computers. Commercial airliners and military planes carry embedded computers that help control the aircraft. Embedded computers also control the movements of industrial robots, maintain the orbits of satellites, and guide modern weapons systems, such as missiles, to their targets.