Forty titles were produced for the Sega 32X, an add-on for the Sega Genesis video game console. Codenamed "Project Mars", the 32X was designed to expand the power of the Genesis and serve as a holdover until the release of the Sega Saturn. Independent of the Genesis, the 32X used its own ROM cartridges and had its own library of games. The product was originally conceived as an entirely new console by Sega of Japan and positioned as an inexpensive alternative for gamers into the 32-bit era, but at the suggestion of Sega of America research and development head Joe Miller, the console was converted into an add-on to the existing Genesis and made more powerful, with two 32-bit central processing unit chips and a 3D graphics processor. Among the titles for the 32X were ports of arcade games Space Harrier and Star Wars Arcade, a sidescroller with a hummingbird as a main character in Kolibri, a 32X-exclusive game in the Sonic the Hedgehog series in Knuckles' Chaotix, and a version of Doom that was noted for its movement and game length issues when compared to other versions of the game. (This list is part of a featured topic: Sega Genesis.)