Windows vs operating system

Windows and operating system both are nouns.

Word	Noun	Adjective	Verb	Adverb
Windows	Yes	No	No	No
operating system	Yes	No	No	No

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

Windows: (trademark) an operating system with a graphical user interface
operating system: (computer science) software that controls the execution of computer programs and may provide various services

Other hypernyms of Windows include OS.

Windows (noun)	operating system (noun)
(trademark) an operating system with a graphical user interface	(computer science) software that controls the execution of computer programs and may provide various services