Dynamic drive overlay (DDO, also referred to as: software translation driver) is a software technique to extend a system BIOS that does not support logical block addressing (LBA) to access drives larger than 504 MiB.
This technique overrides some of the motherboard BIOS' hard disk controller driver in RAM.
To allow access to the full size of any hard disk the software must be loaded before other programs try to access the upper parts of a disk with a critical size.
The application of a Dynamic Drive Overlay (DDO), as licensed to Samsung Corporation for example, by Kroll Ontrack's version in their Disk Manager program is for the installation of various hard drives (Ultra/Super IDE/Parallel ATA) in computers that have older BIOS chips that do not recognize hard disk drives larger than 137.4 Gigabytes.
[1] The interface is a software program that is loaded at start-up by the computer and augments the BIOS code, thus allowing the system to recognize and read areas of the hard disk drive that normally would not be accessible by the older BIOS.