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 (Figure 4-2). And unless you’ve changed the settings, they arrive in the Downloads folder on your Dock.

Figure 4-2. A: This is the downloaded compressed file. Double-click to get… B: The .dmg (disk image) file. Double-click it to “mount” the disk image. C: And now, the disk image itself. Double-click to open the installer window. (Dismiss the warning that the software came from the Internet.) “Eject” it after the installation is complete. D: Here’s the actual installer. After the installation, you can delete all this stuff (except maybe the .dmg file, if you think you might want to install the software again later).
The downloaded file’s name usually has a file name extension like .zip (the standard compression file format for Windows and Mac files) or .dmg (a disk image file, 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 ...
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