I always thought it was purely a hardware limitation, but reading up on it I found it’s actually just “virtual 8086 mode” that was dropped, 16-bit protected mode is still available even when running the CPU in “long mode”.
So it rules out DOS apps, but 16bit Win 3.x apps should still run. But it’s probably a compatibility minefield, and even MS decided it wasn’t important (iirc the only thing they kept around was support for 16-bit app installers, but by internally swapping them out with 32-bit versions when run, since it was apparently common for 32-bit 9x apps to still use 16-bit installers so they could show a proper error message when run under Win 3.x)
I always thought it was purely a hardware limitation, but reading up on it I found it’s actually just “virtual 8086 mode” that was dropped, 16-bit protected mode is still available even when running the CPU in “long mode”.
So it rules out DOS apps, but 16bit Win 3.x apps should still run. But it’s probably a compatibility minefield, and even MS decided it wasn’t important (iirc the only thing they kept around was support for 16-bit app installers, but by internally swapping them out with 32-bit versions when run, since it was apparently common for 32-bit 9x apps to still use 16-bit installers so they could show a proper error message when run under Win 3.x)