For every instance of a device context, the system has a doubleword that is reserved for use by the presentation driver. Typically, this doubleword is used by the presentation driver to hold a pointer to information about the current state of the device context. This pointer is returned to the system by the driver when the device context is enabled. On subsequent calls through the dispatch table, the pointer is passed back to the presentation driver as a parameter (pInstance) on the program stack. For more information, see EnableDeviceContext.