magnetic drum vs memory device

magnetic drum and memory device both are nouns.

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

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

magnetic drum: a cylinder coated with magnetic material, for storing computer data and programs.
memory device: a device that preserves information for retrieval

Other hypernyms of magnetic drum include storage device.

magnetic drum (noun)	memory device (noun)
a cylinder coated with magnetic material, for storing computer data and programs.	a device that preserves information for retrieval