I have a GBA game "Golden Sun". I've played it 16 hours. Then I removed the GBA expansion pack from the DS and didn't start the DS again, so the system could not write the data back to the SD card. I put in the Rumble pack and played another NDS game. For the next 8 hours I didn't put the GBA expansion back in the DS. The next day I put in the GBA expansion back in the system and started the DS Browser. After using the browser I restarted and started another session of Golden Sun. It didn't find a save file on the system (when I looked in the explorer I saw a .0 and a .is0 file). I removed all the files, placed a new Golden Sun GBA file on the system. When starting Golden Sun I have seen a savefile which was from playing 3 hours. So this is probably an old file where I don't know where it came from (there were no .0 or .is0 files of Golden Sun on the SD card). I play for 5 minutes and save. I restart the DS. I receive the message "processing data", so it is creating the 0. and .is0 files. When I start Golden Sun I don't see any savefiles anymore. When I delete the .0 and .is0 files again and start the game I'll supprisingly see the 3 hours save file. Then I restart the DS, it creates the files, after starting the game it's back at 0 hours again. How does the save meganism work? Can anyone tell me what is happening? I'm afraid I will have this also with other GBA games.