Opening Compressed Files with StuffIt Expander
You might have noticed that the downloaded files launch another application whose icon appears briefly in the Dock, as shown in Figure 4.4. That application is StuffIt Expander.
Figure 4.4 When the download is finished, StuffIt Expander goes to work.
You need StuffIt for use with compressed files. Because applications tend to be very large files, they come in a compressed form that takes up less space and makes downloading them faster and easier. These compressed files are also referred to as archive files because they're compact and easily stored.
Compression can be done in several different ways. Mac OS X supports the same methods used on the Macintosh system for the past decade, including .sit (StuffIt) files. In addition, it supports UNIX standards, such as .tar and .gz files.
To install applications that come as archive files, you must return them to their original state. Recovering a full-sized file from its archive file is known as extraction. That's where StuffIt Expander, a tool included with Mac OS X, comes into play.
StuffIt Expander uncompresses most common archive types, and makes it simple for anyone to start downloading software. Most of the time, StuffIt Expander opens automatically when it's needed and leaves uncompressed folders on the desktop along with the original archive file. An example of this was shown in Figure 4.2 (the icon with the .gz text below it).
StuffIt Expander is located on your system at Applications/Utilities/StuffIt Expander. You might never need to start it manually, but you can use a number of settings in its Preferences dialog box to control actions, such as how StuffIt deals with files after extraction.