Classification of Computers

Microcomputers:
A microcomputer's CPU is a microprocessor. The microcomputer originated in late 1970's. The first microcomputers were built around 8-bit microprocessor chips. What do we mean by an 8-bit chip? It means that the chip can retrieve instructions/data from storage, manipulate, and process an 8-bit data at a time or we can say that the chip has a built- in 8-bit data transfer path. 8088 was a 8/16 bit chip i.e. an 8-bit path is used to move data between chip and primary storage (external path), but processing is done within the chip using a 16-bit path (internal path) at a time 8086 is a 16/16 bit chip i.e. the internal and external paths both are 16 bit wide. Both these chips can support a primary storage capacity of up to 1 Mega byte (MB).
Most of the popular microcomputers are developed around Intel's chips, while most of the minis and super minis are built around Motorola's 68000 series chips. There are, however, new trends developing. With the advancement of display and VLSI technology now a microcomputer is available in very small size. Some of these are laptops notebook computers etc. Most of these are of the size of a small notebook but equivalent capacity of an older mainframe.

Minicomputer:

The term minicomputer originated in 1960s when it was realised that many computing tasks do not require an expensive contemporary mainframe computers but can be solved by a small, inexpensive computer. Initial minicomputers were 8 bit and 12 bit machines but by 1970's almost all minicomputers were 16 bit machines. The 16 bit minicomputers have the advantage of large instruction set and address field; and efficient storage and handling of text, in comparison to lower bit machines. Thus, 16 bit minicomputer was more powerful machine which could be used in variety of applications and could support business applications alongwith the scientific applications.

With the advancement in technology the speed, memory size and other characteristics developed and the minicomputer was then used for various stand alone or dedicated applications. The minicomputer was then used as a multi-user system, which can be used by various users at the same time. Gradually the architectural requirement of minicomputers grew and a 32-bit minicomputer, which was called super mini, was introduced. The super mini had more peripheral devices, larger memory and could support more users working simultaneously on the computer in comparison to previous minicomputers.

Mainframes:

Mainframe computers are generally 32-bit machines or on the higher side. These are suited to big organisations, to manage high volume applications. Few of popular mainframe series are MEDHA, Sperry, DEC, IBM, HP, ICL, etc. Mainframes are also used as central host computers in distributed systems. Libraries of application programs developed for mainframe computers are much larger than those of the micro or minicomputers because of their evolution over several decades as families of computing. All these factors and many more make the mainframe computers indispensable even with the popularity of microcomputers.

Supercomputers:

The upper end of the state of the art mainframe machine is the supercomputers. These are amongst the fastest machines in terms of processing speed and use multiprocessing techniques, where a number of processors are used to solve a problem. There are a number of manufacturers who dominate the market of supercomputers-CRAY (CRAY YMP, CRAY 2). ETA (CDC-ETA 10, ETA 20) and IBM 3090 (with vector), NEC (NEC SX-3), Fujitsu (VP Series) and HITACHI (S Series) are same of them. Lately ranges of parallel computing products, which are multiprocessors sharing common buses, have been in use in combination with the mainframe supercomputers. The supercomputers are reaching up to speeds well over 25000 million arithmetic operations per second. India has also announced its indigenous supercomputer.

Supercomputers are mainly being used for number crunching problems such as weather forecasting, computational fluid dynamics, remote sensing, image processing, biomedical applications, etc. In India, we have one such mainframe supercomputer system-CRAY XMP-14, which is at present, being used by Meteorological Department.