The 4 removable roms that are together. I believe 17c, 16c, 15c, and 13c. Also the removable rom in the middle of the board (forgot the number exactly but think it's 6g). Sometime the one rom by itself is surface mounted and you need to put a socket in there. Be sure to hold down the reset button when you boot it the first time with the new roms, this board requires it when changing roms.