Originally an abbreviation for Opcode MIDI System, but was later changed to Open MIDI System, and is now Open Music System. OMS, which was developed by Opcode, is very similar in function and purpose to FMS, or FreeMIDI, and actually predates it as the original standard and widely used method of providing an environment for MIDI on Macintosh computers. The idea is that once OMS learns the configuration of your MIDI system any and all programs that are compatible with it (and virtually all MIDI programs on the Mac are) can get access to and take advantage of that information. That information could include patch names, attributes, and locations of your instruments as well as synchronization sources. Like FreeMIDI it handles all the data throughput between the various hardware and software components of a MIDI system and can even coexist in a system with FreeMIDI.