disk overhead vs disc space

disk overhead and disc space both are nouns.

Word	Noun	Adjective	Verb	Adverb
disk overhead	Yes	No	No	No
disc space	Yes	No	No	No

As nouns, disc space is a hypernym of disk overhead; that is, disc space is a word with a broader meaning than disk overhead:

disk overhead: (computer science) the disk space required for information that is not data but is used for location and timing
disc space: (computer science) the space available on a magnetic disk

Other hypernyms of disk overhead include disk space.

disk overhead (noun)	disc space (noun)
(computer science) the disk space required for information that is not data but is used for location and timing	(computer science) the space available on a magnetic disk