Installing software on a Mac is different from installing software on Windows. There isn’t just one way to install applications on a Mac, either — there are several different ways, depending on the application you want to install.
New Mac users will likely find themselves asking a number of questions: Why isn’t every application on the Mac App Store? What is a DMG file, and why do I have to drag-and-drop the app’s icon after opening it?
Mac App Store
Recent versions of OS X include the Mac App Store, inspired by the iPhone and iPad App Store. Just open the App Store application included with your Mac and you can search for and install apps. Apps automatically update through here, just as they do on iPhone and iPad. For example, Apple’s iWork apps and even new versions of OS X arrive through the Mac App Store. Any apps you purchase from here are also tied to your Apple ID, so you can install them on your other Macs.
The Mac App Store sounds great, and can be very convenient. However, one of the first things you’ll probably learn as a new Mac user trying to install software is that not all the apps you want are available in the Mac App Store.
This can be for a variety of reasons. For example, the Mac App Store sandboxes apps distributed through it, placing limitations on them similar to the ones in place on iOS. This helps protect users, but makes certain types of software impossible. For example, the Twitter app is available through the Mac App Store — it doesn’t need to do anything too powerful. However, any sort of application that needs access to the entire file system wouldn’t be allowed in the Mac App Store.
Given the limitations, many developers still distribute their apps outside the Mac App Store.
Visit a Mac application’s website to directly download the application from the developer and you’ll probably get a DMG file. This is how Mac applications have traditionally been distributed.
A DMG file is a disk image, which is sort of like an archive file. When you download one, you can double-click it to “mount” it, allowing you to extract the application from inside it.
For example, let’s say you wanted to install Google Chrome on your Mac. You’d visit Google’s Chrome download page and download the file — it would be a DMG file. You’d then double-click the DMG file and a window would appear with the Application and a link to your Applications folder.
If you look closely, you’ll see that the DMG file is mounted under Devices in the finder. The window with the the application icon is basically just a Finder (file browser) window that contains several things — the application file (here, Google Chrome), a link to the Applications folder on your computer, and some sort of background image that tells you to drag and drop the icon.
Here, you’d simply drag the application icon to the Applications folder. This copies the application from inside the DMG file to the Applications folder on your computer. This doesn’t happen automatically because the DMG file is just a disk image; it doesn’t have permission to install an app on your computer. You must choose to do that yourself.
After the app is dragged to your Applications folder, you can run it normally — from the Finder, Launchpad, Spotlight, dock, or anything else. The first time you open a downloaded application, you’ll see a warning. Agree to open the file and you won’t see the warning again.
After the app is installed, you don’t need the DMG file anymore. You can “eject” the disk image by clicking the Eject button under Devices in the finder or Command-clicking its desktop icon and selecting Eject. You can then delete the DMG file by moving it to the Trash.
Some developers may not use DMG files. You may end up downloading an Application file itself. In this case, you can drag-and-drop the application file from your Downloads folder to the Applications folder. It will then be installed just like an app that was distributed in a DMG file.
You don’t actually have to install apps to your Applications folder. In fact, you can just place an app in any folder and double-click the application to launch it. Applications are traditionally stored in the Applications folder so they’re organized and located in a single place.
Some apps are distributed in archive files with file extensions like .tar.gz or .tbz. To extract the archive file, simply double-click it. The Archive Utility will automatically extract the contents of the archive to the current folder.
You’ll then get an application file you can drag and drop to your Applications folder.
Some applications, including Microsoft Office, have Windows-like installers. For example, if you want to install the Google Voice and Video plug-in so you can make calls from Gmail and participate in Google Hangouts, you’ll first need to open a DMG file and then double-click the installer, which is a PKG file.
The installer can do additional things that can’t be accomplished just with drag and drop, such as installing system services and placing files elsewhere on the system.
When downloading an app from outside the Mac App Store, the app must be signed by an “identified developer” before it will run — at least by default. This helps protect average users from running a potentially malicious application. This application-signing feature is known as Gatekeeper.
You may run a downloaded application and see a warning saying the application “is damaged and shouldn’t be opened.” Your Mac will say “you should move it to the trash.” This is likely because the application wasn’t signed by its developer, but could also be because a signed application file was tampered with or corrupted during a download process.
If you’re a normal Mac user and aren’t sure why you’re seeing this warning, you’ll probably want to stop here. However, if you know what you’re doing and need to run an application that you trust — but the developer hasn’t signed — you can disable this protection.
To disable Gatekeeper, open the System Preferences window — click the Apple icon at the top-left corner of your screen or click the System Preferences icon on your dock — and click the Security & Privacy icon. Click the lock icon, enter your password, and set the “Allow apps downloaded from” option to “Anywhere.” This will reduce your security as it allows unsigned apps to run, so be sure you know what you’re doing if you use this option.
These different ways of installing software built up over time. The Mac App Store is new, and its limitations prevent it from being used for every Mac application. Gatekeeper has only been around for a few years, too. DMG files are a traditional way of distribution applications, but aren’t required. For some things, installer PKG files are required.