 The operating system and factory sounds are often stored in a Read-only memory (ROM) unit.A MIDI instrument can also be a stand-alone module (without a piano style keyboard) consisting of a General MIDI soundboard (GM, GS and XG), onboard editing, including transposing/pitch changes, MIDI instrument changes and adjusting volume, pan, reverb levels and other MIDI controllers.Typically, the MIDI Module includes a large screen, so the user can view information for the currently selected function.