Interesting question but there is no mention anywhere that I can find of the onboard ROM size or what is actually contained there? I would assume it to be around the same size as the flash memory (4MB) or more and probably contains some Casio system exclusive info, factory settings, version data, demo songs, and some preset tone data. Seeing that you really can’t manipulate this data or “flash it” in anyway, it has no importance in song or sequence creation that I can tell? If anyone knows more about tell