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What are the specific differences between disk image file and .app extension in macOS

vasanths294
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  • I'm not sure how to answer this, since pretty much everything is different between them. It's a little like asking the specific difference between a tuna fish and a cardboard box. Can you clarify what you're actually trying to understand? – Gordon Davisson Feb 21 '20 at 17:40
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    @GordonDavisson The major similarity is: with both facilitate installing an app on your mac. I suppose you only download .dmg files. But never download .app files. They get created off of the .dmg? Is that right? And ultimately how what does a .dmg contain? how is it different from the contents of a .app? What transition needs to happen from a .dmg for it to produce a .app? Is that more clear? – mfaani Feb 22 '23 at 14:59
  • Interesting to note is that other operating systems interpret `.app` files as actually being just a folder, containing the equivalent of what you'd find in the "Program Files" folder in Windows for that program. Within that `.app` folder there's an executable, which is what runs when you click an icon for your `.app`. So, in macOS, `.app`s seem to be folders with some kind of special execution; normally the execute permission for a folder just opens it, in this case it runs an executable present inside them. Don't know enough about `.dmg` to make this an answer right now but I hope this helps. – Alexandre Feb 26 '23 at 05:21

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A disk image file or .dmg is a copy of a disk, a virtual disk. In it's simplest form a disk image is a file containing what would normally reside on a physical device say, a hard drive, thumb drive, floppy disk, etc.

A macOS application or .app file is a bundle or a collection of related resources from the view of the OS. For example the Safari.app bundle contains not just the executable, but Information property lists, resources such as icons, plug-ins, etc. Unlike in Windows, on macOS an application is not just an executable. It can and should be viewed as a self-contained entity that has the necessary frameworks and libraries to function on it's own. This is why you can simply drag and drop a .app to "install" a program on macOS. Finder in macOS treats this bundle as a single entity which is why you can just double click and launch it as if it were just an executable. If you right click and select Show Package Contents on a .app bundle you will see that it more resembles a directory. As an aside, a bundle may contain another bundle inside it, so an .app may have another .app inside such as a helper, sub-tool, etc.

In macOS how is a .dmg related to a .app? They're not really, but the delivery of an application is often done via a .dmg disk. If you download a .dmg from an application provider macOS will mount it as a virtual disk, show you its contents which often contains a bundle with a .app extension that you then copy and paste locally to install the application.

Jav Solo
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