Disk image files may also be managed via the command line interface using the hdiutil utility.

Apple originally created its disk image formats because the resource fork used by Mac applications could not easily be transferred over mixed networks such as those that make up the Internet.

Even as the use of resource forks declined with Mac OS X, disk images remained the standard software distribution format.

Disk images allow the distributor to control the Finder's presentation of the window, which is commonly used to instruct the user to copy the application to the correct folder.

[1] A similar format that supported compression of floppy disk images is called DART.

[10] All values are big-endian (PowerPC byte ordering) The XML plist contains a blkx (blocks) key, with information about how the preceding data fork is allocated.

Whether the encryption is a layer outside of or inside of the blkx metadata (UDIF) is unclear from reverse engineered documentation, but judging from the vfcrack demonstration it's probably outside.

[8] There are few options available to extract files or mount the proprietary Apple Disk Image format.