When you turn on your PC, the BIOS examines each of your PC’s drives, and then loads the first operating system it finds, usually the one on your hard drive: Windows.  But you may want to make your PC start running from an operating system on a CD, either your Windows XP CD or a diagnostic program. Or perhaps you want your PC to find an operating system on a hard drive you’he plugged into a USB port, especially if that hard drive contains a backup of your main hard drive.

That’s when you need to change the “boot order”. You want to tell your PC’s BIOS to look for the operating system first on the floppy drive, then your CD drive, then any “removable drives” like your USB drive, and finally end up looking in the hard drive.

Once you’he changed the drives’s order, the change takes place as soon as save your changes at the BIOS’ Exit screen and restart your PC.