Windows 1.0 was based on early GUIs: Xerox Alto, Apple LISA, etc. From there, Windows co-evolved with Macintosh and Unix, stealing features and having features

Windows 1.0 was based on early GUIs: Xerox Alto, Apple LISA, etc. From there, Windows co-evolved with Macintosh and Unix, stealing features and having features stolen. Windows NT was a total rewrite, which removed the DOS underpinning, and added Unix-style multitasking (and multiprocessor support, and strong FIPS-compliant access control restrictions for their government customers). Windows NT was supposedly based heavily on VMS, although you can't really run VMS in 2021, so there's no way to verify that fact.