## Display Device Driver Reference for OS/2

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### Overview

A virtual video device driver is used by the IBM Operating System/2 as a virtual display device for DOS applications executing in a DOS session by providing virtual hardware support. Virtual video device drivers are required when it is necessary for multiple DOS sessions to share one or more video devices.

The virtual video device driver manages access to video memory, video registers, and video adapter ROM BIOS. Special functions have been defined to permit other OS/2 Ring 3 components (such as the DOS Session Manager and the Presentation Manager display device driver) to obtain the vital video state information necessary to window a DOS session on the Presentation Manager Desktop.

For simplicity, a dedicated virtual video device driver should be targeted to a specific video device. This reference manual includes a set of virtual video device drivers that can be used as templates for enhancement modifications to any of the currently supported devices, or they can be used as samples to create a virtual device driver from scratch for a similar but compatible device. For example, the OS/2 virtual Super VGA device driver (VSVGA.SYS) is a derivative of the virtual VGA device driver (VVGA.SYS).

The following virtual video device drivers, which cover an extensive range of the most commonly used video devices, are included in this reference manual:

Virtual CGA device driverVCGA
Virtual EGA device driverVEGA
Virtual MONO device driverVMONO
Virtual VGA device driverVVGA
Virtual XGA device driverVXGA
Virtual SVGA device driverSVGA
Virtual 8514/A device driverV8514A

The video devices for which OS/2 provides virtual video device drivers include:

Western Digital
ATI
Cirrus Logic
Headland
IBM Super VGA
Trident
TSENG
Video 7**

Note: Specific Super VGA chip revision/model support can be found in VVDP. H.