Cartridges
In early consoles, (consoles released in what is considered to be the 1st generation of video games from 1972 to 1977) the code for one or more games was built into the console, and no additional games could be added. Beginning in 1976 with the Fairchild Video Entertainment System (VES), home video game consoles used cartridges with games stored on them. These cartridges would be sold separately of the game system. The cartridges were Read Only Memory (ROM) chips contained within plastic casing, which were inserted into slots on the console. One benefit of this was that consumers could have full libraries of games instead of being limited to a small selection of games (or even just one game) on a 1st generation console. It also allowed companies to develop "third party games", games developed for various systems by a company that does not have a system of its own. The first third party video game developer was Activision. The three consoles that dominated the market during this period were the Atari 2600 (originally called the Video Computer System), the Intellivision, and the ColecoVision.