## Virtual Device Driver Reference for OS/2

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### Virtual WIN-OS/2 Support Device Driver

The virtual WIN-OS/2* support device driver (VWIN) provides interfaces and transport services which enable DOS and OS/2 applications to do communication between processes in a very fast, event-driven, specialized way. The clipboard, DDE and WIN-OS/2 window functions use these interfaces to exchange data between WIN-OS/2 sessions and the Presentation Manager desktop.

The data and messages which pass through VWIN are not actually inspected nor understood by the driver. Instead, the driver provides a store and forward mechanism. To accomplish this, an interface is exported for each environment. In an OS/2 session, a thread of the OS/2 process blocks in VWIN waiting for data from any of the other processes. In a DOS session and in a WIN-OS/2 session, the address of a notification routine is registered, and this routine is invoked when a message or data is available from one of the other processes using the interface. Interfaces are provided which allow for sending messages and data to other specific processes or for broadcasting to all processes. This system is outlined in the illustration below:

              /------------\       /----------------\
              |   OS/2     |       |DOS or WIN-OS/2 |
              |  Process   |       |      Process   |
              \------------/       \----------------/

                    |    /------------\     |
                    |    |   VWIN     |     |
                    \---|            |----/
                         \------------/