«Types of computers»

Computers can be classified according to the basis of how data are presented; according to the aim and application; according to the architecture, size and portability and according to their technical development.

In this text we'll dwell upon only some types of computers, most commonly known .

General-purpose computers can perform a great variety of tasks; a user can switch from one task to another simply by loading a different application program into memory.

In contrast, dedicated computers are designed for special purposes to perform a very limited set of operations . The programs to carry out these operations are built into the computer and cannot be altered. Dedicated computers are found in automobiles, microwave ovens, navigation systems, and many other helpful applications .

Analog computers. An analog computer is designed to measure something that changed continuously and smoothly, such as voltage or temperature. Data are coded according to voltage rather than by

the presence of absence of a current and are represented as a continuous quality. The drawback is the lack of precision. A good comparison is an old - fashioned watch with hands that move smoothly around the face, mimicking the smooth passage of time. It is easy to know when half a second has passed.

Analog computers generally are dedicated devices . They are most commonly used in working engineering problems.

Digital computers.A digital computers processes discrete numbers. A digital signal is noncontiguous (discrete) but specific -either a 0 or a 1. This is identical to what happens in digital watches, which divide time into tiny bits, making it easy to measure seconds, microseconds, and even nanoseconds .

Divisions among digital computers have been blurred by technological developments but 'our broad categories are still 1 generally recognized .

Microcomputers. A microcomputer has a microprocessor as its CPU and it is designed to serve a single user. However, like other computers, microcomputers can be connected in a network with other microcomputers. This enables communication and the sharing of data among many computer users.

Microcomputers are the most common computers; they are widely used in all types of business as well as in homes and schools. They range in size from desktop models to models as small as a credit card. There also are broad ranges of internal memory, speed and cost. One microcomputer used in many homes and schools has 4MB of memory and costs about $2000, at the other end of scale is a workstation that has 32MB of memory and cost $50 000 or more.

Workstations are fast, powerful microcomputers originally meant to handle engineering and scientific tasks; however, new models are showing up in other work environments - just as more traditional desktop microcomputers are becoming powerful enough to

48

handle engineering and scientific jobs.

Many workstations are based on a relatively new and simpler chip design called RISC (reduced instruction set computing). This design eliminates instructions that are rarely used, putting them in software if needed . Already, RISC computers can outdistance the processing speed of the fastest mainframe computers, and at a lower cost.

Minicomputers. A minicomputer is large, more powerful, and more expensive than most microcomputers. It is designed to be used by more than one person at a time. For example, the cash registers in a grocery store can be connected via a network to a minicomputer, which has a large enough memory to store data on sales of the thousands of different products sold by the store.

Mainframe computers. These are large powerful computers that may fill an entire room, with a CPU as large as refrigerator. They are designed to be used by many people simultaneously. Because of their cost which may be several million dollars, mainframe computers have been used primarily by government agencies, scientific organizations and businesses that require massive record and data storage facilities. For example, mainframe play a central role in airline reservation systems. The ability to network computers, coupled with the dramatic increase in minicompressor speed, is causing many organizations to move away from mainframes. Instead they are used microcomputers linked together by a network.

Supercomputers. The fastest digital computers in existence are called supercomputers. In many ways they are the harbingers of the future: supercomputers of 25 years ago were less powerful than the microcomputers of today: the supercomputers of today will probably be considered dinosaurs 25 years from now. Most supercomputers, as well as other computers, are scalar machines: they operate serially, reading sequential bytes with a single processor, and perform most efficiently when handling repetitive calculations. Today the most powerful supercomputers are parallel computers, which operate on the principle that two processors are

better than one, four better than two, 1000 or more better yet... Parallel computers divide a problem into parts, assigning portions to multiple processor operating simultaneously; each processor calculates subtotals and return them to a central processor for combining. Such a system is much more flexible than the scalar system. The major problem to be solved is keeping synchronization among the processors.

Supercomputer speed is measured in gigaflops, or billions of floating point operations per second. Speeds of 10 gigaflops are now possible, and researchers developing parallel machines predict that speeds measures in treadles, or trillions of operations per second, will be attained in the mid 1990's .

Supercomputers are 40 000 to 50 000 times faster than a typical microcomputer. Their great speed makes it possible to solve problems that would take years on conventional mainframes. Supercomputers are being used to design bridges, airplanes, and nuclear power plants; to do basic research in science and engineering; to conduct weapons research and code cracking; to forecast weather and assist in petroleum exploration, and to create complex graphics and special effects for motion pictures .