Long-time gamers might be familiar with one under-utilized piece of technology from the 1990s: lock-on technology. This was Sega's buzzword that allowed the Genesis (or MegaDrive) cart Sonic & Knuckles to physically connect to other cartridges to enhance gameplay. Up until recently, it was thought that this was only compatible with two existing games: Sonic the Hedgehog 2 and Sonic the Hedgehog 3, allowing the gamer to play as Knuckles in those games. This was until 2005, when a user-created patch added the ability to play as Knuckles in the original Sonic The Hedgehog (full story).