I would imagine that Windows was closer to UNIX than VMS was, and there were several POSIX ports to VMS. VMS POSIX ports: https://en.m.wikipedia.org/wiki/Open

I would imagine that Windows was closer to UNIX than VMS was, and there were several POSIX ports to VMS. VMS POSIX ports: https://en.m.wikipedia.org/wiki/OpenVMS#POSIX_compatibility https://en.m.wikipedia.org/wiki/OpenVMS#POSIX_compatibility VMS influence on Windows: https://en.m.wikipedia.org/wiki/Windows_NT#Development https://en.m.wikipedia.org/wiki/Windows_NT#Development "Microsoft hired a group of developers from Digital Equipment Corporation led by Dave Cutler to build Windows NT, and many elements of the design reflect earlier DEC experience with Cutler's VMS, VAXELN and RSX-11, but also an unreleased object-based operating system developed by Cutler at Digital codenamed MICA." Windows POSIX layer: https://en.m.wikipedia.org/wiki/Microsoft_POSIX_subsystem https://en.m.wikipedia.org/wiki/Microsoft_POSIX_subsystem Xenix: https://en.m.wikipedia.org/wiki/Xenix https://en.m.wikipedia.org/wiki/Xenix "Tandy more than doubled the Xenix installed base when it made TRS-Xenix the default operating system for its TRS-80 Model 16 68000-based computer in early 1983, and was the largest Unix vendor in 1984." EDIT: AT&T first had an SMP-capable UNIX in 1977. "Any configuration supplied by Sperry, including multiprocessor ones, can run the UNIX system." https://www.bell-labs.com/usr/dmr/www/otherports/newp.pdf https://www.bell-labs.com/usr/dmr/www/otherports/newp.pdf UNIX did not originally use an MMU: "Back around 1970-71, Unix on the PDP-11/20 ran on hardware that not only did not support virtual memory, but didn't support any kind of hardware memory mapping or protection, for example against writing over the kernel. This was a pain, because we were using the machine for multiple users. When anyone was working on a program, it was considered a courtesy to yell "A.OUT?" before trying it, to warn others to save whatever they were editing." https://www.bell-labs.com/usr/dmr/www/odd.html https://www.bell-labs.com/usr/dmr/www/odd.html Shared memory was "bolted on" with Columbus UNIX: https://en.m.wikipedia.org/wiki/CB_UNIX https://en.m.wikipedia.org/wiki/CB_UNIX ...POSIX implements setfacl.