[Q]: Как узнать, в FS ли DOS-сессия?

[A]: Alexander Perezhogin (2:5007/2.1)

INT 2F C - OS/2 compatibility box - SWITCHING DOS TO BACKGROUND

       AX = 4001h

Note: called by OS/2 when the DOS box is about to be placed in the

       background and the video driver should save any necessary state

SeeAlso: AX=4002h,AX=4005h

INT 2F C - OS/2 compatibility box - SWITCHING DOS TO FOREGROUND

       AX = 4002h

Note: called by OS/2 when the DOS box is about to be placed in the

       foreground and the video driver should restore the previously-saved
       state

SeeAlso: AX=4001h,AX=4006h