Norton DiskDoubler (DD) was a data compression utility for compressing files on the Apple Macintosh platform. Unlike most such programs, which compress numerous files into a single archive for transmission, DiskDoubler was intended to compress single files "in place" to save space on the drive. When such a file was opened, DiskDoubler would decompress the file before handing it off to the application for use. A later addition, AutoDoubler, added background compression, finding and compressing files automatically when the computer was idle.
[TODO: According to macutil, there are more DiskDoubler formats: an archive format, a self-extracting archive format, and a self-decompressing file format.]
DiskDoubler files have no extension, they maintain the source file name and extension (if used).
DiskDoubler files have the magic number (hex values)
AB CD 00 54 for the first 4 bytes.
The header will also include the Macintosh Type/Creator code for the original source file.
Creator Code is "