Image
What is a .dmg file?
A .dmg file is an UDF Disc Image. This is an image format — a picture, drawing or graphic. Confusingly, this extension has been used by 8 different formats over the years — they're all listed below.
This extension has been used by more than one format
8 different formats have claimed .dmg over the years, so two files with the same extension aren't necessarily the same kind of thing.
- UDF Disc ImageNo version recorded · fmt/1738
- Apple Disk Copy ImageVersion 4.2 · fmt/625
- ISO 9660 Disk Image FileNo version recorded · fmt/468
- Apple Partition Map Disk ImageNo version recorded · fmt/1740
- UDF-ISO 9660 Bridge DiscNo version recorded · fmt/1739
- Apple Disk ImageNo version recorded · fmt/1071
- Hierarchical File System PlusNo version recorded · fmt/1742
- Apple Partition Map - ISO 9660 - UDF Hybrid Disk ImageNo version recorded · fmt/1757
How to open a .dmg file
- GIMP (free) and IrfanView open a very wide range of image formats, including obsolete ones.
- XnView MP is the best bet for unusual or legacy image types.
- Your operating system's built-in viewer may work for mainstream formats.
The registry records this extension against UDF Disc Image, Apple Disk Copy Image, ISO 9660 Disk Image File and others, so software from that family is the most likely match.
How to convert a .dmg file
- Open it in GIMP or XnView and export as .png (lossless) or .jpg (smaller).
MIME type
When a .dmg file travels over the web, servers label it with this MIME type:
application/x-apple-diskimageThe technical record
For archivists, developers and the merely curious: these are the PRONOM registry entries for .dmg.
| Format name | Version | MIME type | PUID |
|---|---|---|---|
| UDF Disc Image | — | — | fmt/1738 |
| Apple Disk Copy Image | 4.2 | — | fmt/625 |
| ISO 9660 Disk Image File | — | — | fmt/468 |
| Apple Partition Map Disk Image | — | — | fmt/1740 |
| UDF-ISO 9660 Bridge Disc | — | — | fmt/1739 |
| Apple Disk Image | — | application/x-apple-diskimage | fmt/1071 |
| Hierarchical File System Plus | — | — | fmt/1742 |
| Apple Partition Map - ISO 9660 - UDF Hybrid Disk Image | — | — | fmt/1757 |