ARCHIVED: What is a disk image?

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A disk image is a file that contains the file structure and contents of a storage device such as a CD-ROM, DVD, or hard drive partition. Disk images are frequently used to create exact duplicates of volumes, and to produce boot disks and software installation media. On some systems (e.g., all versions of Mac OS X), it is possible to mount a disk image; you can then access its contents as if it were a normal (though typically read-only) volume.

Many different disk image formats exist, and with the exception of those that are self-mounting, you will likely need a separate utility to view and copy their contents or to create new images. In Mac OS X, you can easily create disk images using Disk Utility, located in /Applications/Utilities. OS X handles the .dmg format natively; if you need to mount a disk image of a different format, try using Disk Utility or an application such as Toast Titanium. For Windows computers, Norton Ghost is a commonly used program for creating a disk image.