1. Install an Application from Disc or Download  SEE ALSO 3 Add an Application to the Dock 9 Uninstall an Application
Installing an application under Mac OS X is considerably different from the way it's traditionally done under Windows. Because Mac OS X has no central Registry for storing application data (as Windows does), and because Mac OS X applications are single monolithic "bundles"which can be moved around from place to place or from disk to disk as though each application is a single file (rather than being folders full of DLLs and config files, as it's traditionally done in Windows)oftentimes installing an application involves nothing more complicated than dragging an icon from one disk window to another. Some applications under Mac OS X do use installer programs, as is typical of Windows; this is usually the case with large and complex software, such as Adobe Photoshop or Microsoft Office. When an application uses an installer program, it's usually because the installer has to add resources to the system, such as Library frameworks or kernel extensions, or because it allows you to perform a custom installation, containing only a subset of the complete package. (Microsoft Office, for example, allows you to choose between either a drag-and-drop complete install, or an installer program which allows you to select just the parts of Office that you need.) The more complex the software, the more likely you will need to run an installer. 1. Install an Application from Disc or Download 
Applications typically are installed from either a disc (CD-ROM or DVD) or a disk image . In either case, the process for installing the application is generally the same: You must mount the source disk, then open it up to see what the installation procedure is. We will look at both an application that requires an installer program (iTunes), and one that must simply be dragged from its disk image to your Applications folder (Delicious Library, an excellent organizational tool for DVDs, CDs, and books).  KEY TERMS Archive A collection of documents, folders, or applications that are packed into a single file, which is usually compressed so it can be easily downloaded. On the Mac, archives can be Windows-style ZIP files (with .zip extensions), .sit (StuffIt) files, .tar.gz files (for Unix utilities), or disk images. Disk image A specialized kind of archive file, a disk image is a file that when opened acts like a regular disk that you mount on the system. Disk image files end in .dmg or .img ; if you double-click on one, the Disk Utility application opens up and expands the disk image into a virtual disk mounted in the Finder. You can then browse it or manipulate its contents just as you would any real disk.
| 1. | Locate the Source Disc, Archive, or Disk Image An application downloaded from the Internet is usually in the form of an archive file. This file can be either a compressed folder (usually with a .zip, .hqx , or .sit extension) or a disk image. Downloaded files usually appear directly on the Desktop. If you don't see your file there, your browser might be using a different location for its download files. Many web browsers provide a "download manager" tool that allows you to locate a downloaded file and open it automatically. If you're using the Safari web browser, many downloaded applications will unpack, mount, and copy themselves automatically, and even clean up after themselves , leaving only a single icon for the application sitting on your Desktop. If this is the case, you can skip the rest of this task and simply move the icon into your Applications folder for best organization, or just run the application from where it is. TIP Check the Preferences of your web browser to see where it is configured to save downloaded files. Safari, the built-in Mac OS X browser, is normally set up to save downloads to the Desktop, but if you can't find files you've downloaded, the browser might be set to save them somewhere else. | | 2. | Mount the Disk Image If your application is on a CD-ROM or DVD, insert it into the drive. Its icon will appear on the Desktop, or in the Finder's sidebar (if you have configured the Finder to show removable disks in the sidebar). If the application is an archive file downloaded from the Internet, double-click its file icon. If it's a ZIP or SIT archive, StuffIt Expander launches and expand the file into a folder. If it's a disk image, however, Disk Utility launches and transforms the file into a virtual disk, mounted on your Desktop or in the Finder's sidebar. TIP Many browsers, such as Safari, automatically expand archive files when they're done downloading. Safari launches StuffIt Expander to unpack SIT archives; if the downloaded file is a disk image (with a .dmg extension), or if a SIT archive expands into a disk image, Safari opens the disk image and mounts it as a disk on the Desktop. When downloading an application from the Internet, wait until the browser finishes unpacking it to either an application folder (as with GraphicConverter) or a mounted disk image (as with Delicious Library), and then use that item to install the application. | | 3. | Locate the Installer or Installation Instructions At this point, you have the application source disk mountedwhether it's an inserted disc or a disk image. Navigate to the disk's contents in the Finder or double-click its icon on the Desktop. A Finder window opens, showing the disk's contents. TIP It's a good idea to keep the download page open in your browser even after you've downloaded the archive or disk image file; the page often contains useful installation instructions. The window should contain instructions for installation, a "Read Me" document, or a "package" file (which is an installer application that you must double-click). Each application is distributed differently. The Delicious Library disk image, for instance, has clear instructions for what to do next , whereas the installer folder for iTunes contains nothing but a package file. If it's not clear what you need to do, look for a "Read Me" file or other similar instructional document. | | 4. | Install the Application Delicious Library's installation instructions are clear enough: Simply drag the application icon from the disk image folder to your Applications folder. To do this, open a second Finder window by clicking the Finder icon at the far left of the Dock or by pressing  . Then drag the Delicious Library folder from the first window to the Applications folder icon in the second window. Many other applications, however, have an installer program. To install iTunes, for instance, double-click the iTunes.pkg file icon to launch the installer. Follow the onscreen instructions, which direct you to choose an installation disk, accept the user agreement, and restart the computer at the end (if necessary). | | 5. | Put Away the Disc
A disk image can be unmounted (or ejected) just like any other disk. Drag its icon to the Trash in the Dock (which turns into an Eject symbol, labeled Eject ), or click the Eject button next to its icon in the Finder's sidebar. The original disk image file is still there; you might want to create a special folder to keep it in, such as one called Downloaded Software in your Documents folder, in case you need it later (for instance, to reinstall the application or review the installation notes). See 13 Create a New Folder .
If you're installing from an inserted disc, when you eject it (using the same method) the drive door opens, allowing you to remove the disc.
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