hard disk vs fixed disk

hard disk and fixed disk both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard disk	Yes	No	No	No
fixed disk	Yes	No	No	No

As nouns, hard disk and fixed disk are synonyms defined as:

hard disk and fixed disk: a rigid magnetic disk mounted permanently in a drive unit

Other synonyms of hard disk include hard disc.

hard disk (noun)	fixed disk (noun)
a rigid magnetic disk mounted permanently in a drive unit	a rigid magnetic disk mounted permanently in a drive unit