ISO/NKit/RVZ

ISO, NKit, and RVZ formats

GameCube disc images come in several formats that trade size against compatibility. Understanding the differences helps you store a library efficiently without breaking how games load.

ISO and GCM

The plain ISO (sometimes called GCM) is a raw, uncompressed copy of the disc. It is the most universally compatible format and the simplest to understand: every byte of the original is present. The downside is size, since each image is around 1.35 GB regardless of how much real data the game uses.

NKit

NKit shrinks images by removing padding and junk data and can store them in a recoverable way that rebuilds a verifiable original. It comes in ISO and a more compressed variant. It is popular for preservation because it can restore the exact source disc when needed.

RVZ

RVZ is a modern compressed format from the Dolphin emulator project. It uses efficient block compression and is both small and fast to read. Many homebrew loaders now support RVZ directly, making it a strong choice for SD and USB libraries.