English: United States patent No. 4,799,635, detailing the 10NES, a lock-out system shipped with units of the Nintendo Entertainment System outside of Japan. In this system, which is analogous to a door with a lock, the NES unit and a cartridge each contain a distinct chip called the Checking Integrated Circuit, the console one serving as the "lock" and the cartridge one serving as the "key". The two chips are identical, but three of their sixteen pins are wired differently to serve their roles. Two pins for input and output on one chip are wired to the opposing pins on another for both to send and receive data, with a third pin serving as a lock/key setting. The "lock" chip is wired to a capacitor that selects from sixteen possible encryption streams, which the "lock" chip then relays to the "key" chip, after which both chips are instructed to output the stream while reading the input to ensure a match, thus unlocking the cartridge. In case of a mismatch of the streams, the system is reset. Likewise, a cartridge without the "key" chip leads to the system resetting indefinitely. United States patent No. 4,799,635 was cited by Nintendo as the basis for a lawsuit against Atari, Atari Games Corp. v. Nintendo of America Inc., which the former won. The patent has since expired, but Nintendo as of 2023 retains the copyright to the 10NES's source code.