IOS249 allows backup games to work. Then you have custom ios' called cios which help games work. When you install cios', you install those as 249. Any ios thats over 200 is a non nintendo ios. Each game requires a certain ios to allow the game to run. So if a game uses ios38, you need ios 38 installed. If your playing a real copy game that uses that ios, your fine. Its when you run that copy in a backup launcher OR use a backup copy of the game, where things can get tricky. Doing it that way, not only will you need ios38 installed, but youll also need cios38 installed as 249 or else that game wont work. It can get even more confusing but stick to the basics until you run into problems. To easily answer your question, ios249 is used.