What would be required to make Windows compatible with the POSIX operating system out of the box?

Question

The motivation for this question is a far-fetched dream that I have, where a large number of excellent software available on nix platforms could be trivially ported to Windows. Microsoft recently took a new approach to open source and openness in general, so I'd really like to know how viable this situation would be if Microsoft were so inclined. Some of the most specific things that interest me are those that could be done without breaking compatibility in the opposite direction, and perhaps some measure of the amount of effort that will be involved. If there were any specific technical examples that would highlight particular difficulties in doing this, it would also be very useful.

Answer 1

Windows was already like that. The NT kernel itself supports the concept of "personalities" (API levels above the NT level) from the very beginning, to support at least the design of the Win32 API, POSIX API, and OS / 2 API.

The POSIX layer has long been spreading to higher-level SKUs (usually server-related) with different names (Microsoft POSIX / SFU / SUA subsystem), but it never fell into non-specialized use, as it was not universally available (Microsoft never pushed it perhaps for commercial reasons) and because other solutions began to spread (think Cygwin / MSYS / MinGW).

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