Short for Dynamic Drive Overlay, specialized software that allows a BIOS that does not support LBA to access hard drives larger than 528MB.
For the hard drive to be recognized, the DDO must be loaded during the boot sequence, where it installs a small program that replaces some of the BIOS's drive access services with its own routines. In order to access the drive, the user must boot from the drive in which the overlay is installed.
