.GDI File Extension

A GDI file is a copy of the original Dreamcast game and will only work with emulators. It cannot be burned on a CD-ROM like .CDI files. GDI files come from the GD-R discs that Sega Dreamcast used and can only be burned using GD-Roms and blank GD-R discs. GD-ROMs are similar to CD-ROMs except they read or burn GD-R discs, the "GD" stands for Gigabyte Disc. The original Dreamcast GD discs are comprised of 1.2 GB, where around 200 MB of the disc is often dedicated to music tracks which is why BIN files appear.

NOTE: Both CDI and GDI files work for Dreamcast emulators, but GDI is more efficient.