It's a MIDI Voice Module and MIDI Sequencer combined in one package, built by Roland as the MT-300 and reformatted and remarketed for Rodgers as the PR-300. The Voice Module section has a basic General Midi set of 128 instruments and sound effects that may be played from a MIDI instrument along with an additional set that expands it to 300+ voices. The MIDI Sequencer section will record and play back the MIDI data chain of keystrokes, tempo changes, volume changes, voice assignments and more. You may play the organ and the MIDI Voices, record them using the Sequencer and listen to them over again from the file of the MIDI events that the Sequencer has recorded. The PR-300 will save these files in Roland Format on a floppy disk. This disk may be placed in a computer, edited or even emailed to others.The PR-300S [second version of the PR-300] has a few more voices, loads songs to memory automatically up to the first event and will save songs on Roland Format or in SMF format.