Dynamic Drive Overlay (DDO) Software is a program that loads when your hard drive is booted that allows the computer bios to see the entire size of the hard drive. Dynamic Drive Overlay (DDO) software is used on a computer where you have a hard drive installed that is bigger than the computer bios supports. If you are trying to perform data recovery on a computer with a hard drive that uses the Dynamic Drive Overlay (DDO) Software then it can come in handy if your data recovery software can access the hard drive at the hardware level instead of the bios level. The reason you should use a data recovery program that can access the hard drive at the hardware level instead of the bios level when the hard drive is using Dynamic Drive Overlay (DDO) Software is because any data recovery programs that access the hard drive at the bios level will only see the size of the hard drive the bios can access without the Dynamic Drive Overlay (DDO) Software loaded or will not be able to see that the hard drive is installed in the computer system without the Dynamic Drive Overlay (DDO) Software loaded. If this is the case then the data recovery program will not be able to recover you data. The bios will not be able to see the entire size of the hard drive without the Dynamic Drive Overlay (DDO) Software Loaded. The Dynamic Drive Overlay Software will not be loaded if you try to boot the computer from a floppy disk or cd that does not have the Dynamic Drive Overlay Software (DDO) on it. If your data recovery program can access the hard drive at the hardware level instead of the bios level then it does not matter if the Dynamic Drive Overlay (DDO) Software is loaded. You will be able to see and recover the full size of the hard drive as long as the data recovery program you are using can access the hard drive at the hardware level.