[justin_]

AIUI, another big problem with the 80286 was that it did not support returning to real mode after switching to protected mode. This made compatibility a huge issue, which was a big problem for Microsoft. The 80836, besides marking a switch to 32-bit, added virtual 8086 mode, which allowed for emulating real mode after already having switched to protected mode.

https://web.archive.org/web/20021003235610/http://osdev.berl...

This "virtual 8086" mode is what was used for the VMM kernel of Windows 9x, and later the NTVDM system on 32-bit versions of Windows NT. I remember being able to run some DOS software on Windows XP (but it wasn't perfect).