Int 15 Fn D600  - Later Ps/2s - Read Boot Device Id                        [B]

   AX = D600h
   BL = 00h
   DX = device ID

Return: CF clear if successful
       AH = 00h
   CF set on error
       AH = status (86h for function not supported)

See Also: AX=D600h/BL=01h,AX=D601h/BL=00h,AX=D602h