Minicomputers:

These mid-range computers are desk-sized machines.  They have more processing speed and storage capacity than microcomputers.  They are used by medium-size companies or departments of large companies for specific purposes.

Mainframe computers:

   These large computers occupy specially-wired, air-conditioned rooms.  They are capable of faster processing and greater storage than minicomputers. 

They are used by large organizations such as businesses, banks, universities, and government.  Terminals are networked to a mainframe or minicomputer.  They allow users to gain access to the information on the mainframe or minicomputer.

Supercomputers:

This is the most powerful type of computer.  It is also the biggest and most expensive of the computers mentioned so far, even mainframes.  It is used in high-tech areas, such as the military, nuclear weapons, space programs, and weather forecasting.