Int 2F Fn 1680  - Ms Windows, Dpmi, Various - Release Current Virtual Mac  [W]

   AX = 1680h

Return: AL = status
       00h if the call is supported
       80h (unchanged) if the call is not supported

Notes: programs can use this function in idle loops to enhance performance
     under multitaskers; this call is supported by MS Windows 3+, DOS 5+,
     DPMI 1.0+, and in OS/2 2.0+ for multitasking DOS applications
   does not block the program; it just gives up the remainder of the time
     slice
   should not be used by Windows-specific programs
   when called very often without intermediate screen output under
     MS Windows 3.x, the VM will go into an idle-state and will not
     receive the next slice before 8 seconds have elapsed. This time can
     be changed in SYSTEM.INI through "IdleVMWakeUpTime=<seconds>".
     Setting it to zero results in a long wait.
   this function has no effect under OS/2 2.10-4.0 if the DOS box has an
     "Idle Sensitivity" setting of 100

See Also: AX=1689h,INT 15/AX=1000h,INT 15/AX=5305h,INT 21/AH=89h,INT 7A/BX=000Ah