Common Options : Floppy, LS/ZIP, HDD-0, SCSI, CDROM, HDD-1, HDD-2, HDD-3, LAN,
                            Disabled

Details

This feature allows you to select the first device from which the BIOS will attempt to load the operating system from. Note that if the BIOS is able to load an operating system from the device selected through this feature, it naturally won't load another operating system, if you have one on a different device.

For example, if you set Floppy as the First Boot Device, the BIOS will load up the DOS 3.3 boot disk which you have placed in the floppy drive but won't bother to load the Windows XP you have on your hard disk. As such, this feature is useful for troubleshooting purposes or for installing a new operating system.

The default setting is Floppy. But unless you boot often from the floppy drive or need to install an operating system from a CD, it's better to set your hard disk (usually HDD-0) as the First Boot Device. That will shorten the booting process and more importantly, prevent the BIOS from loading up the wrong operating system.