The Nintendo 64 video game console has a library of games, which were primarily released in plastic ROM cartridges. Two small indentations on the back of each cartridge allows it to connect or pass through the system's cartridge dustcover flaps. All regions have the same connectors, and region-locked cartridges will fit into the other regions' systems by using a cartridge converter or by simply removing the cartridge's casing. However, the systems are also equipped with lockout chips that will only allow them to play their appropriate games. Both Japanese and North American systems have the same NTSC lockout, while Europe has a PAL lockout. A bypass device such as the N64 Passport or the Datel Action Replay can be used to play import titles, but a few games require an additional boot code before they can be played.