In addition to receiving messages, drivers must notify clients when certain events occur. MIDI input drivers notify clients by sending one of the following messages using the DriverCallback function.
| MIM_CLOSE | Notifies a client application when a device is closed. |
| MIM_DATA | Notifies a client application when the driver receives a complete MIDI event and is sending the event to the client. |
| MIM_ERROR | Notifies a client application when the driver receives an incomplete MIDI event. |
| MIM_LONGDATA | Notifies the client application when the driver returns a buffer with system-exclusive data to the client. |
| MIM_LONGERROR | Notifies the client application when the driver encounters an error while receiving system-exclusive data. |
| MIM_OPEN | Notifies a client application when a device is opened. |