Opened up Win9x DOS under Virtual PC 2008 on a system running W7 x64 on an i7 processor.
I created the smallest program which is:
0F 1F 00 ; NOP DWORD PTR [EAX]
B8 00 4C ; MOV AX,4C00h
CD 21 ; INT 21h
That causes the system to lock up.
If I remove the 0F 1F 00 then it works just fine. So my question is why does it cause a hang? I confirmed CPUID reports the family as 6 (0110b).