A client application using MCI opens a driver by sending an MCI_OPEN message. This message is intercepted by winmm.dll, which first loads the appropriate MCI driver into the application’s address space, and then sends it the following messages, in the order listed:
Note that the driver does not receive the MCI_OPEN message. Also be aware that DRV_LOAD and DRV_ENABLE are sent only if the driver was not previously loaded.
For more information, see the following topics: