Int 2F Fn 4000  - Windows 3+ (os/2 2.x???) - Get Virtual Device Driver (v  [W]

   AX = 4000h

Return: AL = video virtualization (see #2433)

Note:  this function is used by display drivers to find out what capabilities
     exist for the VDD driver and also trigger the VDD driver to call
     functions 4005h and 4006h.  This function also gives the Video Driver
     hardware access to the video registers.

(Table 2433)
Values for Windows video virtualization:
 01h   does not virtualize video access
 02h   virtualizes the video when in text mode
 03h   virtualizes the video when in text mode or single plane graphics modes
 04h   virtualizes the video when in text mode, single plane graphics modes,
     and VGA multiplane modes
 FFh   virtualizes the video fully