Answer: SNES

Nintendo invested an enormous amount of money in developing and marketing their Super Nintendo Entertainment System and they wanted to maximize the life cycle of the console. Rather than limit games to only accessing the hardware within the SNES console itself, Nintendo built support into the console for in-cartridge processors. When a game came along that needed extra processing power, they could simply add a processor to the board within the cartridge to help out.

The first game to feature such a co-processor was Pilotwings (1991). Pilotwings was followed by dozens of co-processor enhanced titles including: Super Mario Kart, Star Fox, and Mega Man X3. If you’re curious as to whether an old game has an added processor or not, cartridges enhanced with an onboard processor included an additional 16 pins, 8 to each side of the original pins. Simply flip the cartridge upside down and look for the additional pins.