Classification of computers
The computer systems are available in various sizes and with a variety of peripheral or support devices to cover just about every processing need. Because of the variety of computer power and functions available, computers are classified on the basis of purpose, type, and capacity.
Computers Classification based on purpose:
There are either special-purpose or general-purpose computers. Special purpose computers are designed for a specific application or type of application. They are also known as dedicated computers. Many such computers have instructions permanently programmed into them that are designed to perform only one major function. Special-purpose computers are used, to control traffic lights, to control the collection of tolls on certain highways, and in automobiles, weapons, appliances and games etc. General-purpose computers are used to handle a variety of tasks. This is possible by the stored-program concept. By this concept, a program containing a series of instructions is prepared for each application and input to and temporarily stored in the computer. Once stored in the computer's memory, this program can be executed, causing the computer to perform the specific function. After the completion of the execution of this program, another program can be input to the computer and the cycle repeated. That is, the same combination of hardware can be used to execute many different programs. General-purpose computers have the advantage of versatility over special-purpose computers. But typically general purpose computers are less efficient and slower than special-purpose computers when applied to the same task.Computers Classification based on Types: analog and digital
Two types of computers currently available. These are analog and digital computers. Earlier discussion was only on digital computers. An analog computer represents quantities by physical analogies. It represents physical quantities, such as distance, velocity, acceleration, temperature, pressure, or angular position, forces or voltages in mechanically or electrically equivalent circuits. That is, it functions by setting up physical models corresponding to mathematical functions. An automobile speedometer is an example of an analog computing device. It converts the rotational rate of the drive shaft of an automobile into the numerical value of the speed of the vehicle. Similarly, a thermometer functions as an analog device by converting the movement of a column of mercury into a temperature reading. Data inputs to an analog computer results from a measuring processes. These computers are ideal in situations where data can be accepted directly from measuring instruments. The ability to collect data at high speeds and to process data at equally high speeds, makes analog computers uniquely suited to controlling processes of oil refineries, steel mills, weapon systems and similar operations. An analog computer does not require any storage capability as it measures and compares quantities in a single operation. The output from an analog computer is generally in the form of readings on a dial (as in the speedometer and odometer of a car) or a graph on the screen of a cathode ray tube. Analog computers were in use before the invention of the digital computers. There are far more digital computers in use today than analog computers. For the remainder of this book concentration will be on digital computers.Computers Classification based on Types:
The capacity of a computer refers to the volume of data that a computer system can process. Previously a computer's size was an indication of its capacity - the larger the physical size of the computer, the larger its capacity. However, with the current state of micro-miniaturization, measurement is based on the size of a computer by its throughput. Throughput is the amount of processing that can be performed in a given amount of time. Based on throughput, computer systems can be divided into three categories: microcomputers, minicomputers, and mainframe computers, with costs increasing proportional to size.Microcomputers:
Early microcomputers had a limited processing potential and limited choice of input/output devices. Present day microcomputers have wider processing capabilities and support a wide range of input/output devices. Today microcomputers are available with a selection of input/output devices varying from a cassette recorder to a voice synthesizer. In addition to general-purpose computations, microcomputers are used for special purpose applications in automobiles, airplanes, toys, clocks, appliances etc.
High-end super micros are known as workstations. The workstation represents the bridge between the microcomputers and minicomputers. It is a microcomputer with many of the capabilities of larger minicomputers but costing much less. Initially designed for use by engineers and designers, and today they are popular for general uses. These workstations can run more than one application for a user. This is known as multitasking. A workstation is also a multi-user system that can be shared by several users at the same time.
Minicomputers:
A Minicomputer system performs the basic arithmetic and logic functions and supports some of the programming languages used with large computer systems. They are physically smaller, less expensive, and have a small storage capacity than mainframes. Minicomputers are ideally suited for processing tasks that do not require access to huge volumes of stored data . As a result of their low cost, ease of operation, and versatility, minicomputers have gained rapid acceptance from their introduction in the mid-sixties. Some of the larger and expensive minicomputers are capable of supporting a number of terminals in a time-shared mode.Mainframe Computers:
Larger computers generally consist of modules mounted on a chassis or mainframe and are known as mainframe computers. They vary in size, from those slightly larger than a minicomputer to supercomputers (like the Cray and Control Data Cyber computers). Mainframe computer systems offer substantial advantages over mini-computers or microcomputers. Some of these are; greater processing speed, greater storage capacity, a larger variety of input/output devices, support for a number of high-speed secondary storage devices, multi programming,and time sharing.Owing to tremendous expense in operating a mainframe computer, this computer system must be operated efficiently. Operating a mainframe at the required level of efficiency requires a very large and highly trained staff. Mainframe Computer systems are generally used by large businesses, universities, governmental agencies, and the military. These systems are often coupled with other computer systems in a large network to provide enormous computing power. This is what is referred to as a distributed data processing system.
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Supercomputers:
The large and powerful mainframe computer is called a supercomputer. The astronomical cost of the super-computers has limited their development to only a few hundred worldwide. The Cray X-MP, Cray XTS-HE is an example of a supercomputer. Such supercomputers are applied to the solution of very complex and sophisticated scientific problems and for national security purposes of some advanced nations.Smaller, less costly mini supercomputers have been developed by several manufacturers. These computers provide approximately half the power of the supercomputer but at a fraction of the cost. The relative low cost has made the mini-supercomputer an attractive to buy for mid-sized to large applications. Many Wall Street brokerage firms in the United States use computers to speed up the processing of large financial models to keep track of securities that have tendencies to fluctuate greatly.
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