1. Micro Computers: 

The smallest among them are micro computers. They are small in physical size (most of them are desktop system; however, notebook micro computers that can fit into a briefcase are also available). They are economical in terms of costs and are friendly in use. Personal com­puters (PCs) fall into this category.

These computers can be used for small data processing jobs of bigger companies or serve as complete computer systems for small firms. PC can also be connected with bigger computers and be used as an intelligent terminal to a bigger computer. The details regarding their applications in business are included in the last section of this book.

2. Mini computers: 

Mini computers are very popular among medium sized compa­nies. Mini computers offer facilities for faster processing of volumi­nous information. Mini computers, of course, are bigger than micro­computers but smaller than most of their elders called mainframes.

They cost somewhere between Rs. 5 to 15 lac depending upon the configuration. However, these prices are only indicative and are sub­ject to substantial changes over time. The mini computers like VAX 8000 series from Digital Equipment Corporation (DEC) and AS/400 series from IBM have been quite popular in computer aided manufacturing, as well as departmental computers.

3. Mainframes: 

Mainframes are bigger computers, capable of handling data processing needs of, say, head office of a bank, or a big multinational company or may be a public utility office. Mainframe computer systems have larger storage and the speed of processing is also very high.

They also offer the advantage of wider choice with regard to up-gradation of the system in future. They offer features such as par­allel processing. The parallel processing involves combining a large number of processors that break down an application into many sepa­rate parts in order to enhance processing speed.

The speed of process­ing is expressed in terms of 10 to 100 millions of instructions per second (MIPS), and cost somewhere between 1 to 5 million dollars depending upon the configuration. IBM still holds almost 80 per cent of mainframe market with its popular mainframe series IBM System 390.

4. Supercomputers:

Supercomputers have a speed of between 100 to 900 MIPS. They are quite expensive and cost somewhere around 10-30 million dollars depending upon the configuration. The other competitors of Cray supercomputers are machines from NEC of Japan.