Most Sound Generator Makers support two standards, GM and its original standard. For example Yamaha supports XG and GM, while Roland supports GS and GM. When you use a Sound Generator, you have to notify which standard is intended to use. And Reset Command is used to do this.

Reset Command specifies which standard is intended to use. Although Sound Generator processes each datum that is coming from PC, it does not know when the tune was started and when the tune will be ended. It simply process commands from PC. For example, if it receives a command that says "play the note of 'C'", it generates the sound of 'C', or if it receives a command that says "change the music instrument", it changes the music instrument. Therefore after receiving GM Reset Command or GS Reset Command, it operates that mode until it receives another Reset Command.  If it is the background music of homepage, if it does not contain a Reset Command, that music is played with the mode that was used by the prior midi file. It maintains settings of Reverb, Chorus, and Music Instruments, so, there may be a problem. To avoid the problem, a Reset Command is necessary at the beginning of every tune.

GM F0 7E 7F 09 01 F7  GS F0 41 10 42 12 40 00 7F 00 41 F7 XG F0 43 10 4C 00 00 7E 00 F7

Some sequence software have a list window that makes selecting these commands easy. Some sequence software do not require F0 because it puts F0 automatically. When the Sound Generator receives a Reset Command, it begins initialize process, and this process takes a time. Therefore a blank major is needed after the Reset Command before the first note is put.