fixed disk vs hard disk

fixed disk and hard disk both are nouns.

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

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

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

Other synonyms of fixed disk include hard disc.

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