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I am new to mac. I was wondering something.

When I download something from Internet (i.e. filezilla) it appears as a single file contained in a single icon. However when I double click it runs, and it doesn't need to install something.

When I move the file it still works. What I wonder are these programs single files. On windows same programs need installing and have multiple files etc...

What I wonder are this icons are containers or single file programs. How is this different from installable programs?

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up vote 6 down vote accepted

This is one of the wonders of the Mac. Most Mac applications are packaged up in what's called an "application bundle." It's basically a glorified folder that contains all of the code and data for the application. So, instead of having an application installed to C:/Program Files for example, the app is self-contained. These programs don't have to be "installed" as everything they need is already present in that app bundle. Most apps save user preferences and other user data to the ~/Library folder, but the app itself can normally be placed anywhere on your system.

You can run those apps from the Downloads folder, though it's generally better to drag them to the /Applications folder on your Mac. This keeps your apps better organized. And occasionally, some apps are improperly coded to work only from the /Applications folder. It's just best practice to keep everything there, but it's by no means required.

Some Mac apps do have an installer (such as Microsoft Office) as they install files in various places on the machine that are required for the app (such as fonts).

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then sup with ".dmg" files? – Sinan Oct 26 '11 at 21:44
DMG files are a disk image files, and sort of represent a virtual disk drive. Downloading app files over HTML doesn't work so well, so DMGs are one method to package that app for web distribution. It's also a way to package together other files along with the app (like a readme and such) in a slightly cleaner method than a zip file. – chrismanderson Oct 26 '11 at 22:15
It's a widely debated topic over the best way to distribute Mac apps. Obviously the Mac App Store now plays a huge role, but here's a great debate over the options for traditionally distributed apps. – chrismanderson Oct 26 '11 at 22:20
Just FYI, ZIP archives are actually a very bad way to distribute Mac OS X applications, as ZIP does not understand unix permissions. – CyberSkull Oct 27 '11 at 2:25

The Mac OS X Finder displays a single icon for an app bundle directory. This directory usually contains several files, including the executable(s), icon files, some data and information files (such as plists), and etc.

You can see all this stuff by using unix file listing commands from the Terminal command-line.

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