subprogram vs software system

subprogram and software system both are nouns.

Word	Noun	Adjective	Verb	Adverb
subprogram	Yes	No	No	No
software system	Yes	No	No	No

As nouns, software system is a hypernym of subprogram; that is, software system is a word with a broader meaning than subprogram:

subprogram: a set sequence of steps, part of larger computer program
software system: (computer science) written programs or procedures or rules and associated documentation pertaining to the operation of a computer system and that are stored in read/write memory

Other hypernyms of subprogram include computer software, package, software, software package, software program.

subprogram (noun)	software system (noun)
a set sequence of steps, part of larger computer program	(computer science) written programs or procedures or rules and associated documentation pertaining to the operation of a computer system and that are stored in read/write memory