A VDD provides and uses Interrupt 2Fh functions to maximize the performance of the Windows display driver in the system virtual machine. The Interrupt 2Fh functions allow the display driver to access video memory and registers without being trapped. To ensure that VDD can maintain the state of the video controller, however, the display driver must call the Interrupt 2Fh functions to notify the VDD of video changes. The VDD also calls Interrupt 2Fh functions to notify the display driver of changes. For more information about the Interrupt 2Fh functions, see the Microsoft Windows Device Driver Adaptation Guide.