The BIOS firmware supports both Legacy BIOS Mode and UEFI Boot Mode. The default setting is Legacy BIOS Mode. Because some operating systems (OS) support both Legacy BIOS and UEFI BIOS, and some operating systems support only Legacy BIOS, you have the following options:
If the OS being installed supports only Legacy BIOS, you must ensure that the BIOS is set to Legacy BIOS Mode before you do the OS installation.
If the OS being installed supports both Legacy BIOS and UEFI BIOS, you can set the BIOS to either Legacy BIOS Mode or UEFI Boot Mode before you do the OS installation.
The following operating systems do not support UEFI-based BIOS:
Oracle Linux 5.x
Red Hat Enterprise Linux 5.x
Oracle VM 3.0 and 3.1
The Boot Menu screen appears.
The UEFI/BIOS dialog appears.
Note - You cannot configure the boot device priority after switching the boot mode. A system reboot is required to properly populate the Boot Device Priority list with devices that support the chosen boot mode.