disk overhead vs disk space

disk overhead and disk space both are nouns.

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

As nouns, disk space is a hypernym of disk overhead; that is, disk 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
disk space: (computer science) the space available on a magnetic disk

Other hypernyms of disk overhead include disc space.

disk overhead (noun)	disk 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