Term:UEFI [Unified Extensible Firmware Interface]

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UEFI is an acronym for Unified Extensible Firmware Interface. It is occasionally, albeit technically incorrectly, referred to as “UEFI BIOS”.

The UEFI, like the BIOS it is designed to replace, is software built into PCs, and performs functions such as:

  • Power On Self Test (POST)
  • Loading of the operating system from bootable media, such as the installed hard drive, an inserted bootable CD or DVD, or a bootable USB device
  • Acting as a standard interface layer between operating systems and the installed hardware

A UEFI typically has a user interface of some sort that is accessible (only) at power-on, before any operating system is loaded. This UI, which is typically more extensive than previous BIOS UIs, allows many of the configuration options, diagnostics, and other manufacturer-specific functions to be accessed before any operating system is loaded.

One of the more notable, and occasionally frustrating, features of UEFI is “secure boot”. Secure boot allows the boot process to be “locked down” according to the PC manufacturer’s specifications, preventing unauthorized operating systems or boot sources from loading.

Like the BIOS, the UEFI is typically stored in re-programmable ROM, allowing it to be updated using special reprogramming software. Unlike the BIOS, additional portions of the UEFI may be stored on reserved areas of a computer’s hard disk.

UEFI (Wikipedia)

EFI's position in the software stack

The Unified Extensible Firmware Interface (UEFI) is a publicly available specification that defines a software interface between an operating system and platform firmware. UEFI replaces the legacy Basic Input/Output System (BIOS) firmware interface originally present in all IBM PC-compatible personal computers, with most UEFI firmware implementations providing support for legacy BIOS services. UEFI can support remote diagnostics and repair of computers, even with no operating system installed.

Intel developed the original Extensible Firmware Interface (EFI) specifications. Some of the EFI's practices and data formats mirror those of Microsoft Windows. In 2005, UEFI deprecated EFI 1.10 (the final release of EFI). The Unified EFI Forum is the industry body that manages the UEFI specifications throughout.

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