mainframe

(noun) a large digital computer serving 100-400 users and occupying a special air-conditioned room. Synonyms: mainframe computer.

(noun) (computer science) the part of a computer (a microprocessor chip) that does most of the data processing. Synonyms: central processing unit, CPU, C.P.U., central processor, processor. Example: "The cpu and the memory form the central part of a computer to which the peripherals are attached."