To identify which motherboard your Xbox 360 has, there are a few key things to check. The layout of the power supply socket is one of the easiest ways to tell models apart, as different revisions use different connectors. You can also look at the amperage (A rating) printed on the back of the console, which helps narrow it down further. Finally, the manufacturing date can give a good indication of the motherboard revision, especially when used alongside the other details.
