mainframe vs CPU

mainframe and CPU both are nouns.

Word	Noun	Adjective	Verb	Adverb
mainframe	Yes	No	No	No
CPU	Yes	No	No	No

As nouns, mainframe and CPU are synonyms defined as:

mainframe and CPU: (computer science) the part of a computer (a microprocessor chip) that does most of the data processing

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

mainframe (noun)	CPU (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