iNES file format is guilty of badly designed bit packing. Four flags were packed into the lower 4 bits, then Mapper Number was assigned to the high 4 bits. Bu

iNES file format is guilty of badly designed bit packing. Four flags were packed into the lower 4 bits, then Mapper Number was assigned to the high 4 bits. But then they needed more than 16 mappers. They used 4 high bits of the next byte to store the remaining 4 bits, and that was enough... until they needed over 256 mappers.