The term generally refers to a hardware device which connects to a computer via a high-speed serial or USB interface, and provides one or more (often more) MIDI inputs and outputs. A driver package, usually Active-X MIDI on a Windows system or Core MIDI on a Macintosh, serves as a bridge between the MIDI interface and the sequencer software running on the computer. The sequencer sends MIDI messages in a special format to the MIDI interface, containing tags telling it which output to route the data to, and (during playback of a recorded sequence) time tags telling the interface exactly what time to send the data. The time tags provide for improved MIDI timing. When the interface receives MIDI input, it sends the messages to the sequencer with tags telling it what input the messages came fro