GDI (Gigabyte Disc Image) is a common disc image format for the Sega Dreamcast. It stores the disc's data as a .gdi descriptor plus one or more binary track files (usually .bin or .raw). GDI preserves the Dreamcast's original disc structure (multiple tracks, sector layout), making it ideal for accurate backups, burning, and emulation.
Not all games benefit equally from a full GDI. Here is where the "best" GDI reveals hidden flaws in CDI rips: dreamcast gdi best