MDX File Documentation
Summary
An .mdx disc image is a DAEMON Tools Extended Media Descriptor File (also called Media Data eXtended), the single-file successor to the older .mdf + .mds pair. It merges the raw sector data and the disc-layout descriptor into one file, so there is no separate sidecar to lose. Mount it with the free DAEMON Tools Lite and Windows treats it like an inserted CD or DVD, or convert it to .iso for wider compatibility. Its MIME type is application/octet-stream.
Technical details
| Feature | Value |
|---|---|
| Full name | Extended Media Descriptor File (Media Data eXtended disc image) |
| File extension | .mdx |
| MIME type | application/octet-stream |
| Format type | Single-file optical-disc image (binary) |
| Developer | DT Soft (DAEMON Tools) |
| Introduced | Around 2009, to replace the .mdf + .mds pair |
| Replaces | The two-file .mdf (raw data) + .mds (descriptor) scheme |
| Contains | Raw disc sectors + track/session layout + copy-protection structures, in one file |
| Byte order | Little-endian (Windows binary) |
| Magic number | No widely documented fixed signature; identified by DAEMON Tools origin |
| Open standard | No (proprietary to DAEMON Tools) |
| Meant to be | Mounted as a virtual drive, not read as a document |
| Primary application | DAEMON Tools Lite (creator of the format) |
| Also opens in | UltraISO, PowerISO, AnyToISO (mount / extract / convert) |
| Convert to | .iso (universal), .mdf+.mds (split back), .bin/.cue |
| Related extensions | .mdf, .mds, .iso, .bin, .cue |
| Also seen as | Markdown+JSX source, OLAP query, dBASE/FoxPro index (unrelated formats) |
| Platform | Windows (no native macOS or Linux mounter) |
| Specification | DAEMON Tools (closed) |
What is an MDX file?
An .mdx in the disc-image sense is an Extended Media Descriptor File, the optical-disc image format introduced by DT Soft (the makers of DAEMON Tools) around 2009. DAEMON Tools also markets it under the name “Media Data eXtended”. It was created for one specific reason: to collapse the older two-file image scheme — a .mdf holding raw sector data plus a companion .mds holding the disc descriptor — into a single self-contained file.
The extension is reused by several unrelated formats: a Markdown-plus-JSX source file used by React documentation frameworks, a Multidimensional Expressions (MDX) query for OLAP cubes, and an old dBASE/FoxPro compound index. Those are separate things. This article is about the DAEMON Tools disc image, which is a binary file meant to be mounted, not read.
What a disc image actually holds
A disc image is a byte-level copy of an optical disc: the CD or DVD is read sector by sector and those sectors are stored in a file so software can treat the file as if a physical disc were in the drive. The unit of storage is the sector. A CD data sector is 2352 bytes on the medium, of which 2048 bytes are user data in Mode 1; the remaining bytes are sync, header, and error-detection/correction (EDC/ECC) fields. A DVD sector carries 2048 bytes of user data. An image that stores only the 2048-byte user portion is small and ISO-like; an image that stores the full 2352-byte raw sector preserves the subchannel and correction data as well, which matters for faithful copies.
Above sectors sit tracks and sessions. A pure data disc is one data track; a mixed-mode or audio CD has several tracks, each with its own mode (audio tracks are raw 2352-byte samples with no filesystem). Multi-session discs group tracks into sessions written at different times. Any image format that wants to reproduce a disc exactly has to record not just the sector bytes but this map of where each track and session begins and what mode it uses.
The descriptor and the data in one file
The reason DAEMON Tools split the old format into .mdf-plus-.mds was exactly this track/session map. The .mdf was the bulk data — the raw sectors, potentially many gigabytes — while the small .mds was the descriptor: the table of contents describing the sessions, the tracks inside them, each track’s mode and starting sector, and the disc layout the mounter needs before it can present the data. A mounter that had the .mdf but not the matching .mds could not correctly interpret the sector blob, which is why a lost or mismatched sidecar broke the image.
The .mdx merges those two roles. The descriptor metadata and the raw sector data are stored inside the same binary container, so the file is self-describing: everything a virtual drive needs to lay out the disc travels with the sectors. That single-file design is the entire point of the format, and it is why you never need a companion file to mount an .mdx. DAEMON Tools has not published the byte-level layout of the container, so there is no reliable third-party parser and no fixed magic number to key on; the format is identified by its origin.
Copy-protection structures ISO cannot represent
A plain .iso is deliberately simple: it stores only the 2048-byte user data of each sector for a single data track, which is enough to reproduce the ISO 9660 or UDF filesystem and its files. That simplicity is also its limit. An ISO cannot represent multiple tracks or sessions cleanly, cannot store audio tracks, and cannot preserve the low-level artefacts some discs used for copy protection: deliberately bad sectors, unusual sector sizes, subchannel data, or physical layout tricks that a checking routine reads to confirm the “original” disc is present.
Because the .mdx can carry raw full-size sectors plus the full session/track descriptor, it can preserve those structures where an ISO would silently drop them. This is why converting .mdx to .iso is easy but potentially lossy: the filesystem and files survive, but any protection that depended on low-level structure does not. For an ordinary data disc there is nothing to lose; for a protected disc the ISO is a functional copy of the files but not a faithful copy of the medium.
Mounting, converting and splitting
The normal use of an .mdx is to mount it. DAEMON Tools Lite attaches the image to a virtual SCSI/optical device, and Windows then sees an inserted disc with a drive letter; the operating system reads the image’s sectors through the virtual drive exactly as it would a physical one. Mounting is a read operation and is safe in itself — the risk, if any, is in running installers or executables that the mounted disc contains, since disc images were a common vehicle for pirated and malware-bundled software. Scan the contents before running anything.
Converting to .iso (with AnyToISO, UltraISO, PowerISO, or DAEMON Tools itself) is the most useful transformation because ISO mounts natively in Windows 10/11 and on macOS and Linux, none of which have a native .mdx mounter. You can also split an .mdx back into the legacy .mdf + .mds pair for an old tool that expects that layout, or convert it to .bin/.cue for multi-track or audio discs that ISO cannot fully hold (the .cue sheet carries the track list that a single ISO has no place to store).
FAQ
Do I need an MDS file to open an MDX?
No, and that is the whole reason the format exists. The .mdx already contains the descriptor data that a separate .mds used to hold. You only need a companion .mds when you have the older .mdf image, not when you have a single .mdx.
Can I mount an MDX on a Mac?
Not directly. DAEMON Tools’ .mdx mounting is Windows-oriented and there is no native macOS or Linux mounter. Convert the image to .iso on a Windows PC first, then mount the ISO natively on macOS or Linux.
References
Feedback
Was this page helpful?
Glad to hear it! Please tell us how we can improve.
Sorry to hear that. Please tell us how we can improve.