Digital computers are such computers which calculate data on the basis of continuous counting rather than measurement. Digital computers can be classified according to their size, speed, processing capacities, memory, disk storage capacity, cost, application areas etc. The various types of digital computers are given below:
1. Microcomputers
The computers which are based on microprocessors such as Intel 80386, Intel 80846 etc. are known as microcomputers. They are also known as Personal Computers or Home Computers since they can be used by only one person at a time in houses. The word size of microcomputers is 8 to 12 bits. Microcomputers are generally used in the fields like education, training, business etc. Some examples of microcomputers are IBM, IBM Compatibles, Apple Macintosh etc.
2. Minicomputers
These computers are larger than microcomputers and smaller than mainframe computers. They are more powerful than microcomputers in terms of processing power and storage capabilities. These computers are modified from single user concept of microcomputers to multi-single user concept. The word size of minicomputers is 32 bits or even more. These computers are useful for small business organizations and real-time applications like processing control systems. The examples of minicomputers are PDP-8, VAX 7500, HORIZON II etc.
3. Mainframe computers
Mainframe computers are larger in size and the storage capacity and processing speed are higher than that of microcomputers and minicomputers. They have a very high capacity of main memory and can process a huge amount of databases at extremely fast rate. They can support hundreds of users at a time. The word size of mainframe computers is 32 to 64 bits. These computers are suitable for big organizations, banks, industries etc. These days, mainframe computers act as nodes of large national as well as international networks. IBM 4384, CDC-600, CYBEK 170 etc. are the examples of mainframe computers.
4. Supercomputers
Supercomputers are the most powerful computers among all the digital computers. They contain several processors which run together. These make the supercomputers more fast and powerful. Some of the present supercomputers have the computing capability equal to that of forty thousand microcomputers. Supercomputers can execute billions of floating point instructions per second. A Japanese supercomputer has become able to calculate the value of Pie (π) to sixteen million decimal places. John Von Neumann’s architecture was the root of creation of supercomputers. These are multiprocessors, parallel systems with word length equal to 64 bits. They are suitable for complex scientific applications like weather forecasting, military purposes, rocket projection, satellites control etc. The examples of super computers are CARY XMP-24, CDC-7600 etc.
Furthermore, the new design achievement in computer field has evolved and this achievement is also known as Ultra Computer. This will lead to the new generation of computers.