Decide the system's first boot device.
1 - No override
2 - Force PXE
3 - Force boot from default Hard-drive
4 - Force boot from default CD/DVD
5 - Force boot from Floppy/primary removable media
6 - boot flags valid. The bit should be set to indicate that valid flag data is present.
This bit may be automatically cleared based on the boot flag valid bit clearing
parameter, above.(This option is read-only.)
7 - Force boot into BIOS SETUP
The default value is 6 (unspecified)