mainframe computer vs mainframe

mainframe computer and mainframe both are nouns.

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

As nouns, mainframe computer and mainframe are synonyms defined as:

mainframe computer and mainframe: a large digital computer serving 100-400 users and occupying a special air-conditioned room

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