optical disk vs storage device

optical disk and storage device both are nouns.

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

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

optical disk: a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface
storage device: a device that preserves information for retrieval

Other hypernyms of optical disk include memory device.

optical disk (noun)	storage device (noun)
a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface	a device that preserves information for retrieval