What is the difference between the GS and the GM patch set?
GM means General Midi. It is a standard containing 128 patches (sounds). This standard ensures that if you have selected a brite piano on any GM device you will get that sound. The standard is described on the MMA (MIDI Manufacturers Association) pages. GS is a Roland standard which can be thought of as GM + additional sounds. So there are more patches (sounds) then in the GM standard. These additional sounds can be used using bank selection via a sequencer.