"All?" No. Windows NT derivatives are based on VMS, not Unix; in the pre-NT days, DOS was based on CP/M which was loosely based on RT-11. Unix doesn't really show up anywhere in the Windows family tree, aside from the POSIX subsystem added to NT versions pre-XP.
No, Windows NT was not based on VMS. This is a common misconception because Dave Cutler and other VMS developers worked on the project. I've heard this my whole IT career. You can read more about it here:
http://en.wikipedia.org/wiki/Windows_NTDOS was based on QDOS which Microsoft bought from Seattle Computer Products. QDOS imitated CP/M pretty heavily. Microsoft bought QDOS and modified it to fit IBM's requirements. This was then called MS-DOS. You can read more about it here:
http://en.wikipedia.org/wiki/MS-DOSIn all fairness, many companies borrowed heavily from CP/M.
Gary Kildall wrote CP/M as an OS for the new micro-computers that were beginning to arrive. CP/M was written in PL/M (a language which he wrote as a Grad Student - I think) and was influenced by the TOPS-10 Operating System. You can read more about it here:
http://en.wikipedia.org/wiki/CP/MCheers!
-P
