The original Game Genie systems were pass-through devices that attached between a cartridge and the console. Upon starting the console, the player is presented with a menu that they can use to enter a series of characters, referred to as a "code", that reference addresses in the ROM of the cartridge. Each code contains an integer value that is read by the system in place of the data actually present on the cartridge. The Game Genie is covered by US Patent #5112051, "Interfacing device for a computer games system", filed May 30, 1990. This patent expired on May 30, 2010, according to current US patent law.[4]
Because the Game Genie patches the program code of a game, the codes are sometimes referred to as patch codes.[citation needed] These codes can have a variety of effects. Most published codes give the player some form of invulnerability, infinite ammunition, level skipping, or other modifications that allow the player to be more powerful than intended by the developers. In rare cases, codes can make the game more difficult or even unlock hidden game features that developers had scrapped and rendered unreachable in normal play.
The Game Genie sold with a booklet of codes for use with various games available for the system. However, new codes continued to be developed and new games were released after these booklets were published. To address this, Galoob created a paid subscription service where subscribers would receive quarterly code updates. In addition, Galoob also ran advertisements in certain gaming publications, such as GamePro, that featured codes for newer games.