What is a .dmg file?
Apple Disk Image · Disk image · Apple · 2000s
A DMG is the Mac equivalent of an ISO, the standard way Mac apps are downloaded. Double-clicking mounts it as a drive, and you usually drag the app inside to your Applications folder to install it.
What is a .dmg file used for?
A DMG packages a Mac application or files as a mountable disk image, often with a tidy installer window that says to drag the app into Applications.
It can be compressed and even encrypted, and it preserves Mac-specific file attributes that a plain ZIP would lose.
DMG is Mac-only. On other systems you would need special tools, and there is rarely a reason to open one outside macOS.
The most common question is how to open a DMG on Windows, and the honest answer is that you usually should not need to: a DMG almost always contains a Mac app, which will not run on Windows anyway. 7-Zip can peek inside many DMGs, but to install and use what is in one you need a Mac.
How to open a .dmg file
The .dmg format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .dmg file.
Windows
- 7-Zip (partial)
- not natively supported
macOS
- double-click to mount
- Disk Utility
Linux
- 7-Zip (partial)
- dmg2img
Web
- Not applicable
How to convert a .dmg file
You can convert a .dmg file to Mount and install using a conversion tool or the export menu of an app that opens it.
.dmg file signature (magic bytes)
Programs recognise a .dmg file by the bytes at the start of the file, not by its name. These are the signatures for DMG. For a full breakdown, see the DMG file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 6B 6F 6C 79 | -512 | 'koly' trailer near end of file |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .dmg file?
A DMG is the Mac equivalent of an ISO, the standard way Mac apps are downloaded. Double-clicking mounts it as a drive, and you usually drag the app inside to your Applications folder to install it.
How do I install an app from a DMG?
Double-click the DMG to mount it, then drag the app icon into your Applications folder. Eject the image when done.
How do I open a DMG file on Windows?
You can peek inside many DMGs with 7-Zip, but a DMG almost always holds a Mac application that will not run on Windows. If you were after a Windows program, look on the vendor's site for a Windows (.exe or .msi) download instead.
Related formats
Sources
Details on this page were checked against authoritative references: