BIOS supports two boot modes: Legacy BIOS and UEFI. You can set the boot mode using the Boot Menu in the BIOS Setup Utility. Boot mode selection depends on the operating system type and configuration that is installed in the system. Some devices and operating systems do not yet support UEFI and can only boot from Legacy BIOS. Depending on your situation, you might have to specify which mode of BIOS you want to use.
Choose Legacy BIOS Boot Mode to allow host bus adapters (HBAs) to use Option ROMs. Choose UEFI Boot Mode to use UEFI drivers.
When using operating systems that support booting only from Legacy BIOS, the Legacy BIOS Boot Mode must be used. When using operating systems that support booting from Legacy BIOS or UEFI, either mode can be used. However, once a mode is chosen, and an operating system is installed, the installation can be booted only using the same mode that was used for the installation.
The following operating systems do not support UEFI:
Oracle Linux 5.x
Red Hat Enterprise Linux 5.x
Oracle VM 3.0 and 3.1
For updates to this list, refer to the Sun Server X3-2 Product Notes at: http://www.oracle.com/pls/topic/lookup?ctx=SunServerX3-2.
Only devices that support the selected mode are listed on the BIOS Boot screen. If you select UEFI Boot Mode, only boot candidates that support UEFI are listed in the Boot Options Priority list. If you select Legacy BIOS Boot Mode, only boot candidates that support Legacy BIOS are listed in the Boot Options Priority list.
When an operating system is installed using Legacy BIOS Boot Mode, the operating system can be booted only in Legacy BIOS Boot Mode.
When an operating system is installed using UEFI Boot Mode, the operating system can be booted only in UEFI Boot Mode.