For questions about the Unified Extensible Firmware Interface, commonly used in later x86 computers as a replacement of BIOS, as well as in ARM servers and more. UEFI supports booting with and without Secure Boot enabled and legacy booting via CSM.

For questions about the Secure Boot feature read and use:

About UEFI

UEFI firmware provides several technical advantages over a traditional BIOS system:

  • Ability to boot from large disks (over 2 TiB) with a GUID Partition Table, GPT.
  • CPU-independent architecture
  • CPU-independent drivers
  • Flexible pre-OS environment, including network capability
  • Modular design

Excerpt from Wikipedia article about UEFI

AdamW on UEFI boot: how does that actually work, then?

Known issues

  • Some computers support legacy booting, but this feature is not available on all devices and planned to be phased out.
  • Some UEFI firmware implementations from computer manufacturers only support booting through \EFI\BOOT\BOOTX64.EFI from the EFI System Partition, not honoring commands to boot a certain UEFI NVRAM boot entry.

Noteable questions

  • http://askubuntu.com/q/233687/40581

    • Troubleshooting the following error GRUB messages when trying to boot Windows:

      error: can't find command drivemap.
      error: invalid EFI file path
      

BIOS vs. UEFI           BIOS vs. UEFI