Game Genie and Action Replay cartridges
The Game Genie and Action Replay are devices that allow custom
cheat codes to be enabled in various console games. Originally
developed by Codemasters, Ltd.
in the U.K., this technology is known as the Action Replay in
Europe where it was distributed by Datel,
and as the Game Genie in North America, where it was sold by Galoob.
Game Genie cartridges are available for the Sega Genesis,
Sega Game Gear, Nintendo Entertainment System, Super Nintendo
Entertainment System, and the Nintendo Game Boy video game systems.
Each platform requires its own version of the device. Action Replay
cartridges were developed for Super Nintendo Entertainment System,
Sega Megadrive (Genesis), and Sega Master System.
For the most part, Game Genie codes can be used in
an Action Replay and vice versa after a format conversion. However,
this assumes that the same regional version of the game is being
used on both systems. Since games are often modified when released
in various world markets, most Action Replay codes correspond
to European releases, while Game Genie codes correspond to North
American or Japanese releases.
Note: The Action Replay has the added ability to modify RAM addresses,
in addition to ROM addresses. It accomplishes this by inserting
a subroutine which is activated on the "vertical blanking
interrupt" of the screen display.
As a game runs on a video game system, specific locations
in the consoles RAM memory are used to hold important information,
such as the number of lives remaining, shields, ammunition, current
game level, etc. The GG/AR device is able to override the values
in those memory locations, allowing the game to be played with
unlimited lives, always full shields, unlimited ammunition, etc.
This capability is a distinct advantage, especially in games that
don't have built-in cheat codes. A large number of games can now
be mastered by using internal codes from the cartridge, or by
entering custom codes found in magazines, 1-900 tip lines, or
web sites such as this.