each nintendo 64 game pak contains a lockout chip (conceptually similar to the 10nes) to prevent manufacturers from creating unauthorized copies of games and discourage production of unlicensed games. unlike previous versions, the n64 lockout chip contains a seed value which is used to calculate a checksum of the game's boot code. to discourage playing of copied games by piggybacking on a real game pak, nintendo produced five different versions of the chip. during the boot process, and occasionally while the game is running, the n64 computes the checksum of the boot code and verifies it with the lockout chip in the game pak, failing to boot if the check fails.