Use the + and-keys to rearrange devices in the boot order list. You'll generally find the boot order on a screen named Boot or something named similarly. If you want to boot off another boot device, simply move it up in the boot order list. If there are no bootable discs in the DVD drive, the computer would try the next option in the list. This means that the computer will attempt to boot any inserted operating system installation discs or live CDs first.
For example, a typical computer might have the DVD drive higher in the boot order list than the HDD. It's referred to as such because it controls the order in which boot devices are checked for an OS.
