Windows was built with a POSIX layer; it already does this. "Broad software compatibility was initially achieved with support for several API 'personalities',

Windows was built with a POSIX layer; it already does this. "Broad software compatibility was initially achieved with support for several API 'personalities', including Windows API, POSIX, and OS/2 APIs – the latter two were phased out starting with Windows XP." https://en.wikipedia.org/wiki/Windows_NT https://en.wikipedia.org/wiki/Windows_NT