Mainframe

Definition for: mainframe

A "mainframe" originally meant the cabinet containing the central processor unit of a very large computer. After minicomputers became available, the word mainframe came to refer to the large computer itself. The older computers used many large vacuum tubes and generated a lot of heat, thus requiring specially air-conditioned rooms. A single computer might have hundreds of users at a time.

Today, because the large vacuum tubes have given way to transistors, a desktop personal computer can have as much power as a mainframe computer that once filled a whole room. Mainframes in use now often have smaller computers as front end processors.