magnetic disk vs storage device

magnetic disk and storage device both are nouns.

Word	Noun	Adjective	Verb	Adverb
magnetic disk	Yes	No	No	No
storage device	Yes	No	No	No

As nouns, storage device is a hypernym of magnetic disk; that is, storage device is a word with a broader meaning than magnetic disk:

magnetic disk: (computer science) a memory device consisting of a flat disk covered with a magnetic coating on which information is stored
storage device: a device that preserves information for retrieval

Other hypernyms of magnetic disk include memory device.

magnetic disk (noun)	storage device (noun)
(computer science) a memory device consisting of a flat disk covered with a magnetic coating on which information is stored	a device that preserves information for retrieval