One functional difference was the addition of a video input to the cartridge port, added specifically to support the System Changer, an accessory also released in 1983 by Mattel that played Atari 2600 cartridges through the Intellivision. The Intellivision hand controllers could be used to play Atari 2600 games. The System Changer also had two controller ports compatible with Atari joysticks. The original Intellivision required a hardware modification, a service provided by Mattel, to work with the "System Changer". Otherwise the Intellivision II was promoted to be compatible with the original.