Comment by p_ing
> It’s purely Microsoft’s lack of desire to continue supporting that use case.
NTVDM leverages virtual 8086 mode which is unavailable while in long mode.
NTVDM would need to be rewritten. With alternatives like DOSBox, I can see why MSFT may not have wanted to dive into that level of backwards compat.
As I’ve already said in my initial comment, this is not the whole story. (I acknowledge it is the official story, but I want to say the official story, at best, creatively omits some of the facts.)
NTVDM as it existed Windows NT (3.1 through 10) for i386 leveraged V86 mode. NTVDM on Windows NT (e.g. 4.0) for MIPS, PowerPC, and Alpha, on the other hand, already had[1] a 16-bit x86 emulator, which was merely ifdefed out of the i386 version (making the latter much leaner).
Is it fair of Microsoft to not care to resurrect that nearly decade-old code (as of Windows XP x64 when it first became relevant)? Yes. Is it also fair to say that they would not, in fact, need to write a complete emulator from scratch to preserve their commitment to backwards compatibility, because they had already done that? Also yes.
[1] https://devblogs.microsoft.com/oldnewthing/20060525-04/?p=31...