A DMG file is a disk image — a single file that contains an entire copy of a disk or folder, compressed and ready to use on a Mac

When you download software for Mac, you often get a DMG file instead of an installer. DMG stands for "disk image," and it works like a container. Inside it is everything the program needs: the application itself, any support files, and sometimes instructions or a folder shortcut. Your Mac treats the DMG like a mounted disk drive — you can see its contents, drag files out, and install what's inside.

The main reason DMG files exist is that they compress large programs into a smaller download and protect the contents during transfer. They're also Mac-specific, which is why you won't see them on Windows computers. If you've ever downloaded software for Mac and seen a window pop up with an icon you drag into an Applications folder, you were looking inside a DMG file.

Key Takeaways

  • A DMG file is a compressed disk image that holds an entire application or folder, and your Mac opens it automatically when you double-click it.
  • Most DMG files mount as a virtual disk on your desktop, and you install software by dragging the application icon into your Applications folder.
  • You do not need special software to open a DMG — macOS handles it built-in, though Windows users need third-party tools.
  • After you finish installing from a DMG, you can eject it from your desktop like any other disk, and the original DMG file can be deleted.

How to open a DMG file on Mac

Opening a DMG file on a Mac is automatic. Double-click the DMG file in Finder, and macOS mounts it as a disk on your desktop. You'll see a new disk icon appear, usually with the program's name. A window opens showing you what's inside — typically an application icon and an Applications folder shortcut.

From there, drag the application icon into the Applications folder window. This copies the program to your Mac's Applications folder, where you can launch it anytime. Once the copy is complete, you can eject the DMG disk by clicking the eject icon next to its name in Finder's sidebar, or by right-clicking the disk icon on your desktop and selecting Eject.

After you eject the DMG, the original DMG file remains on your computer. You can delete it to free up space — the program you installed is now in your Applications folder and doesn't need the DMG anymore. Some people keep the DMG file in case they need to reinstall, but it's not necessary.

Opening a DMG file on Windows

Windows does not recognize DMG files natively. If you need to open one on a Windows computer, you have a few options, though none are as straightforward as on Mac.

The most common approach is to use third-party software like 7-Zip, WinRAR, or DMG Extractor, which can decompress the DMG and let you see its contents. Download one of these programs, install it, right-click the DMG file, and select the option to extract or open it. The extracted files will appear in a new folder.

Another option is to use an online DMG converter tool, which lets you upload the DMG and download it in a Windows-compatible format like ISO or ZIP. This works if the DMG is small enough to upload, but it requires sending the file to an external server.

If the DMG contains a Mac application, extracting it on Windows won't let you run the program — Mac applications don't work on Windows. You'd only be able to view any documents or files stored inside. For actual Mac software, you need a Mac computer.

What's inside a typical DMG file

Most DMG files you download contain an application and little else. The window that opens shows you the program icon on the left and a shortcut to the Applications folder on the right, making the installation process visual and simple.

Some DMG files include additional items: a README file with setup instructions, license agreements, support documents, or sample files. Professional software sometimes includes multiple applications or plugins bundled together in one DMG. Game DMG files might contain the game itself plus downloadable content or a launcher.

The structure is always the same from the user's perspective: you see what's inside, you drag what you want into Applications or another folder, and you're done. The DMG itself doesn't install anything — it just holds the files and lets you access them.

When you might encounter a DMG file

If you use a Mac, you'll see DMG files regularly. Almost every free or paid application downloaded from the internet arrives as a DMG. Software from the Mac App Store is different — it installs directly without a DMG — but anything you download from a developer's website or from sites like MacUpdate or SourceForge typically comes as a DMG.

Operating system updates and beta versions also come as DMG files. If you're installing an older version of macOS or testing a pre-release version, you'll download a DMG, mount it, and run an installer from inside.

Windows users rarely encounter DMG files unless they're trying to use Mac software or troubleshoot a file someone sent them. If you receive a DMG from a colleague or friend, it was likely created on a Mac and sent to you by mistake, or it's a file they intended specifically for Mac users.

DMG vs. other file types you might see

On Mac, you might also see ISO files, which are disk images similar to DMG but more universal — they work on Windows and Mac. ISO files are less common for everyday software downloads but appear more often in professional or technical contexts.

ZIP files are another common format. A ZIP is a compressed folder that works on both Mac and Windows. When you download a ZIP, it automatically extracts into a regular folder. ZIP files are simpler than DMG files but don't mount as a disk, so they're used differently.

PKG files are Mac installers that run a setup process automatically, similar to EXE files on Windows. If you download a PKG, double-clicking it launches an installer wizard rather than showing you a folder to browse. DMG files are more common for simple applications, while PKG files are used when the software needs to run installation scripts or place files in specific system locations.

Frequently Asked Questions

Do I need to keep the DMG file after I install the application?

No. Once you've dragged the application into your Applications folder and ejected the DMG, you can delete the original DMG file. The application is now installed and doesn't depend on the DMG. Some people keep DMG files as backups, but it's not necessary for the program to run.

Why is my DMG file not opening?

On Mac, a DMG should open automatically when you double-click it. If it doesn't, try right-clicking the file and selecting "Open With" and then "Disk Image Mounter." If the file is corrupted or incomplete, try downloading it again. On Windows, you'll need third-party software like 7-Zip or WinRAR to open it at all.

Can I run a Mac application after extracting it from a DMG on Windows?

No. Mac applications are built for macOS and won't run on Windows, even if you extract them from the DMG. You can view any documents or files inside the DMG, but the application itself requires a Mac to function.

What does it mean when a DMG file says "unverified developer"?

When you open a DMG from a developer that isn't registered with Apple, macOS shows a warning. This is a security check, not a sign the software is dangerous. If you trust the source, you can click "Open" to proceed. This warning appears for many legitimate small developers and open-source projects.

Can I edit the contents of a DMG file?

Once a DMG is mounted, you can't edit it directly — it's read-only. You can extract files from it, edit those files separately, and then move them elsewhere. Creating or modifying DMG files requires specialized tools and is rarely necessary for everyday use.