7. Mode Detection

It is possible to write a program or library that can run in either real or protected mode. This function is supplied so that bimodal code can detect at run time whether it is running under protected mode. Code that only runs in protected mode does not need to perform this test.

To Call

     AX = 1686h
     Execute an Int 2Fh (not an Int 31h)

Returns

     If executing in protected mode under DPMI:
     AX = 0

     If executing in real mode or not under DPMI then:
     AX != 0

Programmer's Notes

• This call will return AX = 0 when the caller is running in protected mode. It will return AX non-zero even when running under environments that support DPMI if the caller is in real (virtual 8086) mode. See section 5.1 for information on entering protected mode.