Video Drivers (Three-Part Model)

• Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Advanced Server version 3.1

Windows NT video display drivers are implemented in three parts: the port driver, the Miniport driver, and the display driver. The following sections provide information on these modules.

Port Driver

The port driver is a hardware independent driver that communicates with the Windows NT IO Manager and the Miniport driver. Only one port driver is needed because it contains no video adapter specific information. The port driver does the following:

• At the direction of IO Manager, the port driver initializes the Miniport driver.
• It handles the synchronization of multithreaded requests, ensuring each single-thread Miniport driver receives requests in the proper order.
• It handles many higher level video driver functions, such as video memory mapping and initializing the video for virtual MS-DOS machines (VDMs).

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Videoprt

Miniport Driver

The Miniport driver communicates directly with the video adapter and contains video adapter specific information. There is a different Miniport driver for every video adapter, but because the port driver handles much of the higher-level functionality of the video display and the Miniport driver need only provide an interface to the port driver, Miniport drivers are very small. The Miniport driver handles mode switching, interrupt requests, and I/O control codes (IOCTLs) not processed by the port driver.

Display Driver

The display driver operates in user mode and communicates between the IO Manager and the Windows NT graphical device interface (GDI) and device driver interface (DDI). The display driver is a portion of the Win32 subsystem, and like the port driver, knows nothing about the video adapter hardware. It does, however, have the ability to request such information if needed by an application.