Although Microsoft started Windows back in 1981, it was not until version 3.0 and 3.1 that Windows became popular in 1990-1992. Note that Windows was not an independent operating system originally. It was a graphical user interface platform that relies on DOS (disk operating system). It was not until Windows 95 that it became independent of an underlying operating system.
Modern Windows operating systems (NT, XP, Vista, 7) all use a “kernel” (core part of an operating system) that shares nothing with DOS. Nonetheless, many old standards of DOS (which in return came from CP/M) remain:
It is interesting to note that Windows never really crossed path with Unix in its history. When the NT (which stood for “new technology”) kernel was developed in 1988, the development team leader Dave Cutler came from DEC with VMS experience. VMS (virtual memory system) was not an Unix operating system.