VPOWERD broadcasts WM_POWERBROADCAST messages to notify applications and Windows-based drivers of changes to the system power state. These broadcasts can be initiated by the user, the timer, or the BIOS. Only user-initiated messages allow for user interaction. In all other cases, drivers must respond to the messages on their own. For detailed information about WM_POWERBROADCAST messages, see the Microsoft Win32 Programmer's Reference.
The Configuration Manager notifies ring-0, plug and play device drivers of power changes by sending configuration messages to these drivers instead of WM_POWERBROADCAST messages. The drivers respond to the configuration messages in a similar manner as Windows-based device drivers respond to the corresponding WM_POWERBROADCAST messages. For more information about configuration messages, see the Configuration Manager documentation.
If the system is running APM 1.1 and a low-level driver rejects a request to change the power mode to suspend or standby, VPOWERD sends a "last request rejected" notification to the BIOS if the request was initiated by the BIOS. Similarly, VPOWERD sends "busy processing last request" notifications to the BIOS as needed.