Mainframe Computers : These are large and expensive computer types capable of supporting hundreds, or even thousands, of users simultaneously. Thus, they are mostly used by governments and large organizations for bulk data processing, critical applications, transaction processing, census, industry and consumer statistics among others. They are ranked below supercomputers.
Mini Computers : Minicomputers are mid-sized computers. In terms of size and power, minicomputers are ranked below mainframes. A minicomputer is a multiprocessing system capable of supporting from 4 to about 200 users simultaneously.
The use of the term Minicomputer has diminished and they have merged with servers.
Micro Computers or Personal Computers : A personal computer is a computer designed to be used by one user at a time. The term microcomputer relates to the microprocessor which is used with a personal computer for the purpose of processing data and instruction codes. These are the most common computer types since they are not very expensive.
Microcomputers Are Classified as Desktop and Portable (Mobile) Computers
The Desktop Computers
Desktop computers are not built to be mobile. They are moved, but only to a new desktop location and with the power supply inactive. There are a number of major differences between computers that are intended to be used in one place as a desktop and portables or mobiles that can be easily moved from one location to another.
Desktop computers are large and heavy in comparison to portables. They can be carried in specially manufactured cases, but only to assist a support engineer in moving, not as a frequent procedure. The monitor, keyboard, and mouse are all separate items on a desktop.
Portable or Mobile Computers
Portable or mobile computers are manufactured with a very important feature; they are portable (are designed for mobility). This means a computer user can be able to move with it from one point to another comfortably. One can also work from any location irrespective of if there is a power source.
1. Are small, compact and light in weight
2. Have their own power in the form of a battery but of course, it does not last forever, thus they have to be plugged to a source of power once in a while.
These portable devices are produced in a variety of sizes and very high processing capabilities. Good examples are Laptops, Palmtops, PDAs.