Any hardware connected to your motherboard that is able to be booted from - like your hard drive, floppy drive, and optical drive - will be listed here. Some newer computers even let you boot from devices like flash drives, network resources, and other sources.
The order in which the devices are listed is the order in which your computer will look for operating system information - in other words, the "boot order."
With the boot order shown above, BIOS will first try to boot from any removable devices - like floppy drives or flash drives. If no removable devices are bootable, BIOS will next try the hard drive, followed by the CD-ROM drive, and finally the network.
To change which device to boot from first, follow the directions on the BIOS setup utility screen to change the boot order. In this example BIOS, the boot order can be changed using the + and - keys. Remember, your BIOS may have different instructions.