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I'm a new Mac user and I've been installing a few different apps for different things. A lot of these use .dmg files.

Why exactly do they all expect me to drag the icon into the application folder? What is the point of this?

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As Macs close the walls more and more (ex Mac App Store) you won't have to. It'll all be done for you... –  user588 Jun 4 '11 at 22:50
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@mankoff: How is making software easier to install and not adding any limitations as to how you can already install software "closing the walls"? –  Mark Szymanski Jun 5 '11 at 3:18
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@Mark Szymanski - Probably because the only way to get your app into the mac store is go through apple, and apple have a lot of limitations on what your software can and cannot do. –  Fake Name Jun 5 '11 at 7:04
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Mark, as much as I hate to say it, there are very significant functionality limitations enforced on apps submitted to the Mac App Store. –  Jason Salaz Jun 5 '11 at 9:02
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This isn't a forum. Please keep it relevant to the original question. –  David Metcalfe Jun 5 '11 at 22:19
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6 Answers 6

up vote 9 down vote accepted

An application on a Mac is just a folder full of files with a .app extension. However, OS X hides this fact from you and displays the folder as a file with an icon. Now when you download something it's very uncomfortable to download folders (without a download manager). Therefore this "App Folder" has to be put inside a single file somehow. This can be done in three ways:

  • Put in a zip file (or comparable file format)
  • Put it in a dmg file (which is kind of a flat file filesystem)
  • Make an installer (which, however, also has to be either in a zip or dmg because those are folders to on a mac)

Since most apps are self-contained and do not need anything besides the App Folder, an installer is not only overkill but also slower than just distributing the app folder.

You can obviously launch apps from wherever you want, it's only a custom or a recommendation to put them into /Applications as it easier for you to find it again and it works with multiple users.

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No one has invented a .zip knock off that will automatically extract itself to the proper place (or a place of your choosing?) –  Drew Jun 5 '11 at 1:13
    
Well there's self extracting stuff, but that's basically a dumbed down installer, which - again - is a folder on OS X. Also it's fairly insecure to just let it install wherever it wants to. I suppose apple could have just wrapped up a file extension (say .appzip) which would be just a renamed zip file, which extracts itself into /Applications when executed, but I don't exactly know why they didn't. Maybe it's just for historical reasons. –  XQYZ Jun 5 '11 at 8:00
    
Regarding "or a place of your choosing": most extraction apps (The Unarchiver at least) can be configured to ask for a destination folder when extracting files. –  XQYZ Jun 5 '11 at 8:03
    
@Drew think of this way: how is "automatically extracting itself to a proper place or a place of your choosing" any easier than giving a shortcut to the default (proper) place and allowing you to move it to any place of your choosing through using the OS own means? Well, I answer you: it's not. This is just a paradigm of what you're used to do. –  Cawas Jun 7 '11 at 13:34
    
XQYZ there's at least one added benefit of using DMG - it will keep file permissions as they were intended to be. I've had issues using ZIP to "install" software before, mostly because I was using an alternate unzipper app, but nevertheless even that's a risk DMG won't suffer. –  Cawas Jun 7 '11 at 13:39
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The /Applications folder is just a convenient place to store all of your applications. You can theoretically story them anywhere. Some software (such as Butler) will automatically search for applications in these standard locations, so if you store them elsewhere (such as /Users/Shared/Applications) such software won't find them by default.

Generally there are three standard places to store applications, and 99% of Mac users only work with the first one:

  • /Applications (available to all users)
  • /Users/username/Applications (available to the logged in user who owns that folder)
  • /Developer/Applications (available to all users, used for Xcode software)
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You don't have to put your new Applications in the Application folder - it's just the default place to put them.

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You can create /Applications/Imaging, /Applications/Internet, etc. if you want categorize them. Just don't move any of the standard applications into these folders because further updates will expect them to be directly in /Applications.

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Keep in mind there are plenty of applications that assume they are in a folder called "Applications" and apps that looks for other specific apps in the "Applications" folder.

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DMG files are compressed and read-only. Applications frequently need to be able to update or change components inside themselves; at a minimum, when a new version is detected and it offers to install an update - it won't be able to delete itself and put the new version in its place. Indeed, you'll probably find that running an application off a DMG will result in an "was downloaded from the internet" message on every launch. That doesn't happen if you move it to the right place.

Running an application off a locked DMG is a sure-fire way to run into problems. Just drag the application to some place on your hard disk - preferably one of the Applications folders.

There are certain locations on your Mac that have special significance to the system - these are places where the Mac goes looking for launchable applications when you double-click a document. They include the top level Applications folder, and a folder called "Applications" in your personal home folder. Mounted DMGs are not part of this, if only because they're not always mounted.

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