A Program Change message is limited to only 128 values, while some synthesizers can store many thousands of separate patches. This would mean that only 128 of the programs could be accessed via MIDI. Patch mapping is a process whereby a given program change number received by a MIDI device can be linked to any one of the available patches, as determined by a patch map. To get beyond the 128 limit, the MIDI Continuous Controller message, Bank Select, has been defined for selecting different banks of sounds prior to sending a program change number.