| Microsoft DirectX 9.0 |
System messages are not exclusive to any channel. There are three kinds, as shown in the following table.
| Message type | Purpose |
| System common | Miscellaneous commands and data |
| System exclusive | Equipment-specific commands and data |
| System real-time | Synchronization of clock-based MIDI equipment |
Unlike other MIDI messages, system exclusive messages can contain any number of data bytes. After transmitting the data, the sequencer sends a system common message called an EOX, which signals the end of the system exclusive message.
In DirectMusic, the DMUS_SYSEX_PMSG structure contains the length of the data and a pointer to an array of data bytes.