(Often abbreviated "sysex") A part of the MIDI standard that allows synth manufacturers to define their own specific message formats. Unlike every other message format in the MIDI standard, sysex messages can be variable in length; they are marked by both a start byte (F0 hex) and an end byte (F7 hex). The byte after the start byte is required to be a number that identifies the manufacturer; the MIDI standard defines a specific number for each manufacturer that has applied for an ID from the MIDI Manufacturer's Association. (Because the number of manufacturers has long since exceeded what can be accommodated with a single seven-bit byte, an escape code which allows larger numbers has been defined.) A later revision of the standard added bytes after the manufacturer ID that specify a model