A .GCM file is a digital image of a Nintendo GameCube game. It's often used in collaboration with an emulator to recreate the experience of playing the console on a different medium, usually a computer. A .N64 file is a digital image of a Nintendo 64 game, and is used for the same purpose. As video games are most often read-only memory -- or ROM -- both .GCM and .N64 are types of ROM images. Converting a .N64 ROM into a .GCM ROM allows a user to play a Nintendo 64 game on a GameCube emulator. There are three methods to convert a .N64 ROM into a .GCM ROM.