Note: This API calls are shared between DOS and Win16 personality.
DPMI is a shared interface for DOS applications to access Intel 80286+ CPUs services. DOS DMPI host provides core services for protected mode applications. Multitasking OS with DOS support also provides DMPI in most cases. Windows standard and extended mode kernel is a DPMI client app. Standard and extended mode kernel differs minimally and shares common codebase. Standard Windows kernel works under DOSX extender. DOSX is a specialized version of 16-bit DPMI Extender (but it is standard DPMI host). Standard mode is just DPMI client, exnhanced mode is DPMI client running under Virtual Machime Manager (really, multitasker which allow to run many DOS sessions). Both modes shares DPMI interface for kernel communication. The OS/2 virtual DOS Protected Mode Interface (VDPMI) device driver provides Version 0.9 DPMI support for virtual DOS machines. Win16 (up to Windows ME) provides Version 0.9 DPMI support.
DPMI host often merged with DPMI extender. Usually DPMI extender provide DPMI host standard services and DOS translation or True DPMI services.
Int 2FH, AH=16H, AL=86H
Returns information about the current CPU mode. Programs which only execute in protected mode do not need to call this function.
AX = 1686H
if executing in protected mode AX = 0
if executing in real mode or Virtual 86 mode AX = nonzero
Some environments support programs or libraries that can execute in either real or protected mode (bimodal code). This function is supplied so that such programs can detect at run time whether they are running in protected mode and make use of system facilities accordingly. This function should not be used to determine if a DPMI host is present. A client should make sure that DPMI services are available before calling this function; otherwise, the results returned by the function may not be valid.
Text based on http://www.delorie.com/djgpp/doc/dpmi/