Int 2F Fn 1687  - DOS Protected-mode Interface - Installation Check        [E]

   AX = 1687h

Return: AX = 0000h if installed
       BX = flags
       bit 0: 32-bit programs supported
       CL = processor type (02h=80286, 03h=80386, 04h=80486)
       DH = DPMI major version
       DL = two-digit DPMI minor version (binary)
       SI = number of paragraphs of DOS extender private data
       ES:DI -> DPMI mode-switch entry point
   AX nonzero if not installed

See Also: AX=1686h,AX=43E0h,AX=DE01h/BX=4450h,AX=FB42h/BX=0001h

See Also: INT 31/AX=0400h,INT 31/AX=5702h,INT 38/AH=10h

Call mode switch entry point with:
   AX = flags
       bit 0: set if 32-bit program
   ES = real mode segment of buffer for DPMI private data (ignored if
       SI was zero)

Return: CF set on error
       program still in real mode
       AX = error code (DPMI 1.0+)
          8011h unable to allocate all necessary descriptors
          8021h 32-bit program specified, but 16-bit DPMI host
   CF clear if successful
       CS = 16-bit selector corresponding to real-mode CS
       SS = selector corresponding to real-mode SS (64K limit)
       DS = selector corresponding to real-mode DS (64K limit)
       ES = selector to program's PSP (100h byte limit)
       FS = GS = 0
       high word of ESP = 0 if 32-bit program
       program now in protected mode

Note:  this entry point is only called for the initial switch to protected
     mode