Intro I was trying to play Super Mario Bros. 2 (J) on my DS one day, and I just couldn't get it to work. I found all my FDS roms worked on the computer, but wouldn't work on the DS. After trying different configurations and files repeatedly, I found that the only roms that worked were the ones with an extra 16 bytes. After fixing my roms, I realized that this fix was not easily findable (if existent) on the internet, so that is the reason for this post. Requirements •A broken rom (duh) •A hex editor or a terminal or a command line or whatever your os calls it •A way to tell the exact size of the rom •You DON'T need the FDS Bios •A DS with a flashcart with nesDS working (test with .nes roms first) The Fix If a FDS rom is working on a computer emulator but not on nesDS, then it is likely that there is 16 bites missing from the beginning of the rom. The way to check for this is to look at the exact size of the rom. The size should read: •65516 bytes for a 1 sided disk •131016 bytes for a 2 sided disk •Haven't tested this with 3 or 4 sided disks If the size is 65500 or 131000, then it is likely that the first 16 bytes are missing. If so, open the rom in a hex editor. Paste one of the following lines at the beginning of the rom. For 1 sided disks: For 2 sided disks: For 3 sided disks: For 4 sided disks Alternatively, use the copy command on Windows or the cat command in UNIX to add one of the attached files to the beginning of the rom. Windows: copy FILEINTHISPOST+YOURROM DESTINATION UNIX: cat FILEINTHISPOST YOURROM > DESTINATION If both methods don't work, then you probably are experiencing a different issue than I was. I can try to help you though if you describe your issue in this thread. Notes: •To change sides, go to game -> extras -> fds, and click one of the buttons there. •The first 3 bytes say FDS, the fifth is the number of sides to the rom. •I still have no idea what the fourth byte means... but it seems important. •It's probably best to add the 16 bytes to the rom before you apply a patch for a translation or such. •Make sure you unzip the files before patching. •First post here, hope I didn't break any rules, norms, unwritten rules, EULAs, DS flash carts, hearts, etc.