A video game console emulator is a program that allows a personal computer or video game console (cross-console emulation) to emulate a different video game console's behavior. Emulators are most often used to play older video games on personal computers and video game consoles, but they are also used to play games translated into other languages or to modify (or hack) existing games. Emulators are also a useful tool in the development process of homebrewed demos and new games for older systems.
Code and data of a game are typically supplied to the emulator by means of a ROM file (a copy of the data contained on a game cartridge) or a disc image (for systems that use optical media). Most game titles are copyrighted -- although there exist various sources for such files on the internet, their distribution is prohibited under many legislations. Specialized adapters such as the Retrode allow emulators to directly access the data on game cartridges without the need to copy it into a ROM image first.