## Display Device Driver Reference for OS/2

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### Overview

Each seamless windows session is run as a protect-mode DOS session. The seamless session runs a copy of the Windows video display driver, modified to operate seamlessly. Seamless windows drivers write directly to the video display hardware, and must be modified to coordinate and serialize hardware access. As a result, a seamless windows driver actually "owns" a piece of the PM Desktop.

In addition to modifications to the PM and Windows drivers, the IBM Operating System/2 itself has been modified to support seamless operation. A special virtual device driver (VWIN) is used to establish limited addressability to a small set of key PM routines and data, as well as to provide services permitting hardware serialization and exchange of Windows state-change information.

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