UEFI BIOS supports both Legacy and UEFI boot modes when starting the system. You can set the UEFI-BIOS boot mode using the UEFI BIOS setup utility. UEFI-BIOS boot mode option selection depends on the operating system type and configuration that is installed on the server. Choose Legacy BIOS boot mode to allow HBAs and Express Module devices to use option ROMs. Choose UEFI boot mode to use UEFI drivers.
The BIOS firmware controls the system from power-on until an operating system is booted. The BIOS is based on the Unified Extensible Firmware Interface (UEFI) specification.