Set up the firmware in UEFI or BIOS/CSM/Legacy mode

Some recent computers (>2011) allow you to set up the computer to boot either in UEFI mode or in BIOS/CSM/Legacy (not-EFI) mode. The way to adjust this setting depends on the computers, but generally this setting is located in the "Boot order" tab of the BIOS (to access the BIOS screens, it is generally necessary to press a key during the PC startup). It can also often be set on a per-boot basis by hitting a function key (F8 and F10 are common choices) soon after you power on the computer.

Note: Some UEFIs (e.g. American Megatrends' "Aptio", found on the Asus vivobook series) call Legacy mode "Compatibility Support Module" or simply "CSM".

Remark: Some UEFIs enable one to set up the boot mode for the optical drive separately from the boot mode for the HDD.

For example, below:

• the "UEFI Hitachi" line allows to boot the HDD in UEFI mode,
• the "P1: Hitachi" line allows to boot the HDD in Legacy (not-UEFI) mode,
• the "P3: DVD" line allows to boot the Ubuntu CD in Legacy mode
• the "UEFI: USB" line allows to boot the Ubuntu liveUSB in UEFI mode.

Here is a 2nd example of UEFI boot mode setting, where the "Boot Mode" parameter enables one to choose the boot mode ("UEFI" or "Legacy") for all media (hard disk, CD, USB...) at the same time.

Some other UEFIs propose an "UEFI/Legacy Boot:" option with the following choices: [Legacy only], [UEFI only] and [Both]. This last one boots in UEFI mode when possible, then in Legacy mode if no UEFI files are detected.