Display driver initialization occurs when Windows first boots. When booting, Windows loads the display driver and calls the driver's initialization routine.
The only requirement for the initialization routine is that it must return one in the AX register; otherwise, Windows will fail to load. Although the initialization routine can carry out any task, many drivers do the following:
Typically, drivers wait until GDI calls the driver's Enable function before fully initializing the video hardware.
The initialization routine returns one if the initialization was successful. Otherwise, it returns zero and Windows immediately terminates.