The UEFI specification was primarily intended for the next generation of IA architecture-based computers, and is an outgrowth of the “Intel® Boot Initiative” (IBI) program that began in 1998. Intel’s original version of this specification was publicly named EFI ending with the EFI 1.10 version. In 2005 The Unified EFI Forum was formed as an industry-wide organization to promote adoption and continue the development of the EFI specification. Using the EFI 1.10 specification as the starting point, this industry group released the follow on specifications renamed Unified EFI. The current version of the UEFI Specification can be found at the UEFI web site.
UEFI (Unified Extensible Firmware Interface) will be a specification detailing an interface that helps hand off control of the system for the pre-boot environment (i.e.: after the system is powered on, but before the operating system starts) to an operating system, such as Windows* or Linux*. UEFI will provide a clean interface between operating systems and platform firmware at boot time, and will support an architecture-independent mechanism for initializing add-in cards.
The Basic Input/Output System (BIOS) served as the OS-firmware interface for the original PC-XT and PC-AT computers. This interface has been expanded over the years as the “PC clone” market has grown, but was never fully modernized as the market grew. UEFI defines a similar OS-firmware interface, known as “boot services” and “runtime services”, but is not specific to any processor architecture. BIOS is specific to the Intel x86 processor architecture, as it relies on the 16-bit “real mode” interface supported by x86 processors.
While UEFI uses a different interface for “boot services” and “runtime services”, some platform firmware must perform the functions BIOS uses for system configuration (a.k.a. “Power On Self Test” or “POST”) and Setup. UEFI does not specify how POST & Setup are implemented.
UEFI is an interface. It can be implemented on top of a traditional BIOS (in which case it supplants the traditional “INT” entry points into BIOS) or on top of non-BIOS implementations.
Platforms using the existing EFI 1.10 specification are already in the market place. Platforms using the UEFI specification will enter the market as the specification is developed by the Forum.
Any firmware implementation has to take care to address security. UEFI does not change that for better or worse.