Does OS X installs the app or does the app itself handles the job

[RumorToRuleThemAll]

I come from a Windows background. When you wanted to install a program on Windows you actually let the program itself handle the full install job. This obviously introduces potential security risks as you give a program, at time of installing, full control over your computer. Therefore Microsoft introduced an alternative, so called .msi files. When you wanted to install a program given as an .msi file you let Windows itself install to program, a huge difference reducing the security risk.

Now my question is, how does installing an app on OS X works? Does OS X takes care of the job or does the app itself do the install job?

 

[KALLT]

To a large extent, macOS has a different concept of ‘installing’. By far most programs are distributed as so-called ‘app bundles’. These are what you see in your Applications directory. They have an ‘.app’ extension, which is hidden by default (see picture). App bundles are self-contained programs and they immediately run. They can technically run from any location, it does not matter where you put them. By convention, they are put in the Applications directory. In Windows, most programs live in ‘C:\Program Files’ by default, in separate folders each filled with files. There is no meaningful definition of ‘installing’ in relation to app bundles, other than copying/moving them to your Applications directory. Uninstalling an app bundle is as easy as moving it to Trash.

Sometimes, applications are distributed as installer packages, very much like on Windows. They appear as ‘.pkg’ files (usually with a brown/yellow package icon). These are opened by Apple’s Installer application. Installer will then follow the developer’s instructions and install the application. Installer packages are usually used when some additional setup or configuration is necessary. For example, if the program needs to start immediately after booting (even before logging in) or if it contains kernel extensions (such as drivers). Packages are risky for the reasons you mentioned, so I would be careful when using them, especially when they ask for administrator privileges. Applications that you install with such packages are a bit tricky to uninstall. Most often, the developer will give you detailed instructions or an uninstallation program/script.

The App Store uses installer packages under the bonnet too, but the installation is handled automatically. App Store applications should be deleted by going to Launchpad, where you click and hold the app icon and press on the small X icon on it.

 

[Fishrrman]

Some Mac apps (often upper-end commercial ones) come with an installer app.
Launch the installer, set your options, and it does the rest.
The app goes into the Applications folder, and various "support" folders are created elsewhere where necessary (usually within your home folder).

Other Mac apps come in a "dmg" file.
Double-click the dmg file and it will open on the desktop.
Often there is an alias of the Applications folder displayed, as well.
Just "drag and drop" the app "into" the Applications folder.
Often, no other action is necessary.

Or... you can do the same thing in the finder.
Just drag an app into the Applications folder, and that's it.

With some "utility" type apps, I drag them into the Utilities folder (which is inside the Applications folder). You'll probably need to enter your password for this move.

 

[MacForScience]

There are two general install methods on OS X:
1.) Drag And Drop Install - where you simply drag the application to the Applications folder and you are done. The application may create additional files in Application Support etc when run, but the install is drag and drop complete.

2.) Installer based applications. These applications are based around a .pkg file. A pkg file is a compressed bundle (BOM) of files that the Installer.app in OS X unpacks into the specified directories. The install process also allows for verification of compatibility and pre and post install scripts that can interact with the OS.

You can get a better idea of PKG contents and what they do with Suspicious Package app.