What is the CDI file format?
.cdi files are used for storing disc images created with the DiscJuggler software tool, developed by Padus, Inc. A disc image not only contains all the data stored on the cloned disc, but also captures the physical layout of the data on the disc - session boundaries, track types, and sector-level structure. Unlike a simple file copy, a .cdi image preserves the entire disc structure, allowing a bit-accurate burn to be made from the file.
.cdi images can be generated for optical discs such as CD and DVD, including multi-session and rewritable variants. The format stores raw optical-disc sectors (commonly 2352 bytes per sector in Mode 2) with no compression. Rather than a conventional file header, the raw sector data begins at byte zero; a trailing descriptor block at the end of the file records session, track, and image version metadata. Three internal image versions exist: 2, 3, and 3.5.
DiscJuggler is a now-discontinued disc authoring tool. It was capable of creating images of virtually any type of optical disc. The tool was especially popular among console gaming enthusiasts because it could copy Sega Dreamcast game discs - the Dreamcast's MIL-CD self-boot layout requires a multi-session image that a plain .ISO cannot represent. As a result, .cdi became the de-facto image format for Dreamcast game distribution. Today, Dreamcast images are more commonly stored in the .GDI or .CHD formats for long-term preservation. Note that .cdi should not be confused with Philips CD-i Green Book discs, which share the same extension.
Security & safety
RISK: MEDIUMThe CDI container is passive disc data, but most .cdi files in circulation are Dreamcast game backups obtained from ROM/abandonware sites, which raises both legal (copyright) and malware concerns about the host site. Scan extracted contents before running. DiscJuggler itself is abandonware with no safe official download, so avoid "DiscJuggler" links on repack/crack portals; use IsoBuster, GDRom Explorer, or the open-source Dreamcast CDI Burner instead.
Format details
in a nutshell- DVDInfoPro CD/DVD image - Some DVDInfoPro versions also wrote .cdi disc images, unrelated to DiscJuggler's layout.
- Philips CD-i (Compact Disc Interactive) - The 1990s CD-i interactive disc system is sometimes abbreviated CDI but is a disc standard, not this file format.
Programs that open CDI files
Windows5 apps
DiscJuggler
Paid The original creator app - opens and burns CDI natively, but it is abandonware with no safe official download. 
IsoBuster
Freemium Open the CDI to browse its sessions/tracks and extract files; strong for reading odd disc-image layouts. Free tier reads CDI. 
Alcohol 120%
Paid Mount or burn the CDI image (legacy tool; only needed for burning to physical CD-R). 
GDRom Explorer
Free Open the Dreamcast CDI to browse and extract game files, or convert between Dreamcast image formats.
Redream (Dreamcast emulator)
Freemium Load the .cdi directly to play the Dreamcast game; no burning needed. 
Linux2 apps
Dreamcast CDI Burner (DCDIB)
Open-source Burns all four Dreamcast .cdi self-boot layouts to a CD-R from the command line; the modern free route for real hardware.
Flycast (Dreamcast emulator)
Open-source Load the .cdi directly to play the Dreamcast game on Linux/Windows/Android. Technical details
deep spec| Developer | Padus, Inc. |
| Format type | Proprietary binary optical-disc image |
| Byte order | Little-endian |
| Sector size | Typically 2352 bytes per sector (raw Mode 2 / Mode 1 depending on source disc) |
| Image format versions | 2, 3, and 3.5 - determined by a version field in the trailing descriptor, not a file header |
| File structure | Raw optical-disc sector data from byte 0; session and track descriptor block appended at the end of the file |
| File identification | No fixed magic bytes at offset 0; identified by file extension and by parsing the trailing descriptor block |
| Track type support | Stores mixed-mode images combining data tracks (Mode 1/Mode 2) and audio (CD-DA) tracks in a single file |
| Multi-session support | Yes - captures multi-session layouts including the Sega Dreamcast MIL-CD self-boot session structure |
| Self-contained format | Single-file format - no separate cue sheet or track files required, unlike BIN+CUE |
| MIME type | application/x-discjuggler-cd-image (unofficial); application/octet-stream (generic fallback) |
| Typical file size | 100 MB - 800 MB for CD-sized images; Dreamcast game images typically 500-800 MB |
| Compatible operating systems | Windows (DiscJuggler native); Linux via Flycast, cdirip and other third-party converters |
| Notable use case | De-facto disc image format for Sega Dreamcast game distribution - preserves the MIL-CD multi-session self-boot structure that a plain ISO cannot represent |
| Superseded by | ISO / BIN+CUE for general PC disc images; GDI and CHD for Dreamcast game preservation |
| Released | Late 1990s (Padus DiscJuggler CD-burning software) |
| Latest version | DiscJuggler v6 image (last DiscJuggler release ~2008) |
| Specification | en.wikipedia.org |
CDI conversions
Community Q&A
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