## Virtual Device Driver Reference for OS/2

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### DOS Session Screen Switching

The OS/2 Session Manager notifies the DOS Session Manager of screen switches. The DOS Session Manager, in turn, notifies all virtual device drivers that are involved in these events (generally, the video, keyboard, and mouse virtual device drivers). The virtual video device driver (VVIDEO) takes appropriate steps to map in physical or logical video RAM and disable or enable I/O port trapping for the video hardware. The virtual keyboard device driver (VKBD) can set flags to control the reaction to keyboard polling behavior.