Intel Extensible Firmware Interface - Manual (Page 27)

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Introduction
This Extensible Firmware Interface (hereafter known as EFI) Specification describes an interface
between the operating system (OS) and the platform firmware. The interface is in the form of
data tables that contain platform-related information, and boot and runtime service calls that are
available to the OS loader and the OS. Together, these provide a standard environment for
booting an OS.
The EFI specification is designed as a pure interface specification. As such, the specification
defines the set of interfaces and structures that platform firmware must implement. Similarly, the
specification defines the set of interfaces and structures that the OS may use in booting. How either
the firmware developer chooses to implement the required elements or the OS developer chooses to
make use of those interfaces and structures is an implementation decision left for the developer.
The intent of this specification is to define a way for the OS and platform firmware to communicate
only information necessary to support the OS boot process. This is accomplished through a formal
and complete abstract specification of the software-visible interface presented to the OS by the
platform and firmware.
Using this formal definition, a shrink-wrap OS intended to run on Intel ® architecture-based
platforms will be able to boot on a variety of system designs without further platform or OS
customization. The definition will also allow for platform innovation to introduce new features and
functionality that enhance platform capability without requiring new code to be written in the OS
boot sequence.
Furthermore, an abstract specification opens a route to replace legacy devices and firmware code
over time. New device types and associated code can provide equivalent functionality through the
same defined abstract interface, again without impact on the OS boot support code.
The EFI specification is primarily intended for the next generation of 32-bit Intel architecture
(IA-32) and Itanium
® -based computers. Thus, the specification is applicable to a full range of
hardware platforms from mobile systems to servers. The specification provides a core set of
services along with a selection of protocol interfaces. The selection of protocol interfaces can
evolve over time to be optimized for various platform market segments. At the same time the
specification allows maximum extensibility and customization abilities for OEMs to allow
differentiation. In this, the purpose of EFI is to define an evolutionary path from the traditional
“PC-AT”-style boot world into a legacy-API free environment.