magnetic disc vs memory device

magnetic disc and memory device both are nouns.

Word	Noun	Adjective	Verb	Adverb
magnetic disc	Yes	No	No	No
memory device	Yes	No	No	No

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

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

Other hypernyms of magnetic disc include storage device.

magnetic disc (noun)	memory 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