OS X Mountain Lion: The Missing Manual

Other Ways to Get Mac Software

In general, new programs arrive on your Mac via one of two avenues: as an Internet download (whether from the App Store or not), or on a CD or DVD.

Downloading Compressed Files

Programs you download from the Web (not the App Store) generally arrive in a specially encoded, compressed form. And unless you’ve changed the settings, they arrive in the Downloads folder on your Dock.

The downloaded file’s name usually has one of these file name extensions:

• .zip is the standard compression file format for Windows and Mac files. In fact, OS X has a built-in Compress command right in the File menu.

• .sit indicates a StuffIt file, the standard Macintosh file-compression format of years gone by.

• .dmg is a disk image, described below.

You may occasionally run into .tar files (tape archive, an ancient Unix utility), .gz (gzip, a standard Unix compression format), or combo formats like .tar.gz or .tgz.

Fortunately, you generally don’t have to worry about any of this; most Web browsers, including Safari, automatically unzip and unstuff downloads of all types.

Disk images (.dmg files)

Once you’ve downloaded a program, it often takes the form of a disk image file, whose name ends with the letters .dmg (second from the top in Figure 5-2).

Disk images are extremely common in OS X. All you have to do is double-click the .dmg icon. After a moment, it magically turns into a disk icon on your desktop, which you can work with just as though it were a real disk (third from the top in ...