MIDI Machine Control (MMC)
MIDI messages for the transport buttons — play, stop, record, wind — so one machine can drive another.
MMC joined the MIDI specification in the early 1990s, when studios mixed tape machines, ADAT decks and early sequencer software and wanted a single set of buttons for the lot. Commands travel as Universal Real Time SysEx, so they fit down ordinary MIDI cables without new connectors. Beyond play and stop there are punch-in, punch-out and locate, which winds to a given timecode.
MMC only says what the machine should do, not where it is. Position comes from MIDI Time Code, so the two usually travel together: MMC as the remote, MTC as the clock. Today the protocol survives mostly in DAWs and hardware recorders that still understand it, while control surfaces tend to speak Mackie Control instead.