Extensible Firmware Interface

Extensible Firmware Interface
The Extensibile Firmware Interface specification defines a model for the interface between operating systems and platform firmware. The interface consists of data tables that contain platform-related information and boot and runtime service calls that are available to the operating system and its loader. Together, these provide a standard environment for booting an operating system and running pre-boot programs. Microsoft supports Extensibile Firmware Interface as the only firmware interface to boot Windows XP. Because the 64-bit version of Windows will not boot with BIOS or with System Abstraction Layer (SAL) alone, Extensibile Firmware Interface is a requirement for all Intel Itanium-based systems to boot Windows.

The IA-64 architecture defines the following three firmware layers:

•	Processor Abstraction Layer
•	System Abstraction Layer
•	Extensibile Firmware Interface

The Processor Abstraction Layer, System Abstraction Layer and Extensibile Firmware Interface layers work together to provide processor and system initialization for an operating system boot. Processor Abstraction Layer and System Abstraction Layer provide machine check abort handling and other processor and system functions which would vary from implementation to implementation.

The System Abstraction Layer is a firmware layer that isolates the operating system and other higher-level software from implementation differences in the platform, while the Processor Abstraction Layer is the firmware layer that abstracts the processor implementation.