Microcomputers or Personal computers: Microcomputers are small in size. They can fit on a desk top. These computers are used by a single person at a time.
Minicomputers: Minicomputers have large memory and are costlier than microcomputers. These computers can be used by many people at the same time.
Mainframe computers: Mainframe computers are very large in size. These computers have very large memory and are very costly. They operate at very high speed. They can be used by several persons at the same time. They are used at places such as banks, research organisations, etc. The largest and fastest Mainframe computers are called Super computers.