The server's BIOS firmware controls the server from power-on until an OS is booted.
For administration, BIOS provides the BIOS Setup utility which enables you to view server information, and to configure, enable and disable server components.
The server's BIOS can be configured to operate in one of these two modes:
Legacy BIOS (default) – Supports all of the supported OSs, but does not offer the latest BIOS features.
UEFI BIOS – Provides the latest BIOS features, but only supports these OSs:
Oracle Enterprise Linux
Oracle Solaris
Oracle VM
SUSE Linux Enterprise Server
Red Hat Enterprise Linux
Microsoft Windows
When using OSs that support booting only from Legacy BIOS, you must use Legacy Boot Mode. When using OSs that support booting from Legacy BIOS or a UEFI BIOS, you can configure the BIOS for either mode. However, once you choose a mode, and an OS is installed, the installation can only boot using the same mode that was used for the installation.
Ensure that the server's BIOS is configured for your desired mode before you install an OS. Refer to Server OS Installation for information about changing the BIOS mode.
You can use ueficonfig to capture and preserve the BIOS configuration if you intend to change the BIOS mode. For information about ueficonfig, refer to the Oracle ILOM documentation library at http://www.oracle.com/goto/ILOM/docs.
The advantages to choosing a UEFI-based BIOS installation include the following:
Avoids Legacy Option ROM address constraints. For more information, see Enable or Disable I/O Resource Allocation.
Supports OS boot partitions greater than 2 TB in size.
PCIe device configuration utilities are integrated with BIOS Setup utility menus.
Bootable OS images appear in the boot list as labeled entities. For example, Windows boot manager label versus raw device labels.