C.P.U. vs mainframe

C.P.U. and mainframe both are nouns.

Word	Noun	Adjective	Verb	Adverb
C.P.U.	Yes	No	No	No
mainframe	Yes	No	No	No

As nouns, C.P.U. and mainframe are synonyms defined as:

C.P.U. and mainframe: (computer science) the part of a computer (a microprocessor chip) that does most of the data processing

Other synonyms of C.P.U. include central processing unit, central processor, CPU, processor.

C.P.U. (noun)	mainframe (noun)
(computer science) the part of a computer (a microprocessor chip) that does most of the data processing	(computer science) the part of a computer (a microprocessor chip) that does most of the data processing
	a large digital computer serving 100-400 users and occupying a special air-conditioned room