Could you elaborate? In what I've learned (in the past few minutes) it looks like it hasn't has POSIX compatibility since an optional subsystem up to Windows 2000.
https://en.wikipedia.org/wiki/POSIX#POSIX_for_Windows
Elaborate on what? You have to purchase a version of Windows that has the POSIX layer because POSIX compliance costs money. From what I gather it has been dropped in Windows 8.1.