Purpose: These files are primarily used to burn Dreamcast games onto standard CD-R discs.

• CDI: Modified images often altered for size reduction or self-boot capabilities. Historically used for burning to CD-Rs.
• GDI: 1:1 sector-by-sector dumps of the original GD-ROM. This is the gold standard for modern preservation but requires more storage space.

1. Dreamcast Homebrew Brewery Vol. 1 – A compilation of 50 indie games.
2. Shenmue (CDI 4-disc set) – The Echelon release, downsampled but faithful.
3. Smash Pack (CDI) – Includes Virtua Cop 2 and Sega Swirl.
4. RetroArch Dreamcast CDI – Turns your Dreamcast into an emulation box.
5. Ikaruga (NTSC-J to NTSC-U patched CDI) – The legendary shmup.

• Data Structure: CDI files store the complete contents of a Dreamcast GD-ROM disc, including the initial High Density area and the Low Density area (audio track).
• Compression: Unlike raw dumps, CDI files often utilize proprietary compression methods to reduce file size, stripping out "dummy data" used by developers to push game data to the outer rim of the disc for faster reading speeds.
• Session Data: The format retains the multi-session architecture required for the Dreamcast boot sequence, specifically the "IP.BIN" bootstrap file located in the first session.