retrieval vs machine operation

retrieval and machine operation both are nouns.

Word	Noun	Adjective	Verb	Adverb
retrieval	Yes	No	No	No
machine operation	Yes	No	No	No

As nouns, machine operation is a hypernym of retrieval; that is, machine operation is a word with a broader meaning than retrieval:

retrieval: (computer science) the operation of accessing information from the computer's memory
machine operation: an elementary operation that a computer is designed and built to perform

Other hypernyms of retrieval include computer operation.

retrieval (noun)	machine operation (noun)
the act of regaining or saving something lost (or in danger of becoming lost)	an elementary operation that a computer is designed and built to perform
the cognitive operation of accessing information in memory
(computer science) the operation of accessing information from the computer's memory