The 747 has 2 ailerons per side, inboard and outboard. They are know as low speed (outboard) and high speed (inboard)ailerons, there are of different areas, the outboard being of a larger area. The outboard ailerons are automatically locked out when certain conditions are met, the reason being that the turning moment produced by these is far greater than the inboard ailerons and it would be almost impossible to fly as the inputs required to roll would be so small even the best pilot in the world wouldn't be able to fly it, as far as I am aware it is not to do with aileron reversal.