memory vs ROM

memory and ROM both are nouns.

Word	Noun	Adjective	Verb	Adverb
memory	Yes	No	No	No
ROM	Yes	No	No	No

As nouns, ROM is a hyponym of memory; that is, ROM is a word with a more specific, narrower meaning than memory:

memory: an electronic memory device
ROM: (computer science) memory whose contents can be accessed and read but cannot be changed

memory (noun)	ROM (noun)
an electronic memory device	(computer science) memory whose contents can be accessed and read but cannot be changed
the power of retaining and recalling past experience
the cognitive processes whereby past experience is remembered
something that is remembered
the area of cognitive psychology that studies memory processes