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

   AX = 1680h

Return: AL = 00h if the call is supported
   AL = 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 3.0, DOS 5+,
     DPMI 1.0+, and will be supported 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

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