Computers can be classified into various types, depending upon the technology used or the size and capacity or the applications for which they are designed.
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Based on the purpose or application, computers are often classified as general-purpose computers and special-purpose or dedicated computers.
General-purpose computers are comparatively more flexible and thus can be used to work on a large variety of problems including business and scientific problems. For example, banking applications such as financial accounting, pay-roll processing, etc. at a business organization head office would require the services of a general-purpose computer.
The size and capacity of a general-purpose computer could vary, depending upon the quantum of data and the complexity of data processing to be done.
These types of computers are designed for a dedicated application. They are used to perform a certain predetermined and fixed sequence of operations.
Typical applications include the computers used for weather forecasting, aircraft control systems, missile & weapons guidance systems, etc.
Based on the technology used, the computers may be classified as:
In analogue computers, the input data comprise of continuously changing electrical or nonelectrical (temperature, pressure, speed, volume, etc.) information. An example of analogue computational device is the speedometer of an automobile. The input data to this device or machine is the continuously varying rotational speed of its driveshaft. The rotational motion is converted into a linear movement of a needle pointer that indicates the speed in km/h. A tachometer used to measure the rotational speed is another device of the same type.
The input data in the case of a digital computer are discrete in nature. They are represented by a binary notation in the form of 0s and 1s.
A hybrid computer is a mixture of the two. It attempts to combine the good points of both analogue and digital computers. In a typical hybrid computer, the measuring functions are performed the analogue way while the control and logic functions are digital in nature.
Based on their size, and capacity, computers can be classified as follows:
Mainframe computers are the largest, fastest computer and one of the most expensive computer systems of general use.
Mainframe computers have a large primary storage capability and have a very high processing speed. Because of their size and speed, mainframe systems must be placed on special platforms that allow wiring and cooling systems. They are very useful because of their enormous storage capacity and their capability to support a large number of terminals.
Contemporary mainframe computers are defined by their high-quality internal engineering, reliability, technical support and security features, along with their performance qualities.
Mainframe computers applications include the processing of a huge amount of different kinds of data such as census, industry/consumer statistics, financial transactions processing, etc. in large private and public enterprises, government agencies, etc.
Examples of mainframe computers include Nonstop systems from HP, System z9 servers, IBM’s zSeries, etc.
A minicomputer relatively resembles a mainframe system except that it is comparatively smaller and less costly. They represent a class of multi-user computers that are used for middle-range computing applications, in between the mainframe systems and the microcomputers.
PDP-8 and PDP-11 from Digital Equipment Corporation (DEC) are examples of the popular minicomputers developed in the late 1960s.
The microcomputer which was developed largely as a result of the development of the microprocessor is a compact, relatively inexpensive and complete computer.
A basic difference between mainframe system and microcomputer is the physical size. Whereas a mainframe system may fill a room, a microcomputer may be put on a desktop or fit in a brief case.
Like mainframe systems, and minicomputers, modern day microcomputers, can do data processing, manipulate lists, store, retrieve and sort information. Unlike mainframe systems and minicomputers, microcomputers do not require any specialized environment for operation and can be effectively made use of by people who do not have any comprehensive formal training in computer methods. In actual fact, microcomputers are designed to be used both at workplace and at home.
A personal computer, popularly referred to as a PC, is a stand-alone microcomputer that is used in a varied range of applications, from present day desktop publishing, playing video games, performing simple graphics, simple financial accounting to preparing spread sheets, and so forth.
With the advent of microprocessors and related peripherals, the PC of today is as powerful as a minicomputer of yesteryears. The processing speed has reached GHz and the hard disk capacity has reached tens of GBs. The modern microprocessors for the PC platform offer applications including internet, audio, streaming video, image processing, video content creation, speech, computer-aided simulation and design, multimedia and multitasking user environments.
Depending upon the size and portability, personal computers can be classified as desktops, laptops, and tablets.
Desktops are PCs for use on a desk in an office or at home. Laptops are mobile PCs that can be carried in a briefcase. They do not always require an external power source and run on rechargeable batteries for given period of time.
Workstations are high-end technical computing desktop microcomputers designed primarily to be used by one person at a time, but they can be connected remotely to other users if necessary. They offer high performance compared with a personal computer, especially with respect to graphics, processing power and multitasking ability. Presently, workstations use most technologies that are common to the PC computers.
Supercomputers are the fastest and most powerful of all computer systems. They are typically 200 times faster than the mainframes. Supercomputers are mainly used for calculation-intensive applications requiring enormous amounts of data to be processed in a very short time. These may include weather forecasting, breaking secret codes, designing aircraft, molecular modelling, physical simulations, etc. Supercomputers are mostly used in universities, scientific research laboratories, etc.
Supercomputers are highly parallel systems, that is, they perform many tasks simultaneously. They generate a lot of heat and require a proper cooling mechanism.
Examples of supercomputers include: Intel ASCI Red/9152, IBM Blue Gene/L, Cray X-MP/4, etc.
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