1 What Is a DMG File?

A Mac-specific file format.

A .dmg file (Apple Disk Image) is macOS's equivalent of a virtual CD/DVD. It's a container file that, when opened, "mounts" as a virtual drive on your desktop. This is how most Mac software is distributed — when you download an app from a developer's website, it usually comes as a .dmg file.

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Think of it like this: A DMG is like plugging in a USB drive that exists only as a file. Double-click it, it "plugs in," you copy the app out, then you "eject" it.

2 Opening a DMG on Mac

This is native to macOS — no extra tools needed.

1

Double-click the .dmg file

macOS automatically mounts the disk image. A new window will open showing the contents.

2

Drag the app to your Applications folder

Most DMGs show the app icon and an arrow pointing to the Applications folder. Just drag the app icon over. If there's no Applications shortcut, open a new Finder window and drag the app to Applications manually.

3

Eject the DMG

Right-click the mounted drive icon on your desktop (or in Finder's sidebar) and click "Eject." You can also delete the original .dmg file to save space — you don't need it after installing the app.

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"App can't be opened because it is from an unidentified developer" — Right-click the app → "Open" → click "Open" in the dialog. This only needs to be done once. macOS is just being cautious with apps downloaded outside the App Store.
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3 Opening a DMG on Windows

Got a DMG but you're on a PC? Here are your options.

Windows can't open DMG files natively since they're a Mac format. However, you have a couple of options:

7-Zip can extract the contents of most DMG files. Right-click the DMG → 7-Zip → "Extract Here." You'll get the files inside, though Mac applications won't run on Windows.

If someone sent you a DMG and you need the files inside, ask them to re-send as a ZIP file instead. If they sent you a Mac application, it won't work on Windows regardless of how you extract it.