hard disk vs hard disc

hard disk and hard disc both are nouns.

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

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

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

Other synonyms of hard disk include fixed disk.

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