Plug and Play BIOS Specification

Plug and Play BIOS Specification 1.0A Page 8
2.0 System BIOS Initialization _____________________
The Power On Self Test (POST) procedure of a system BIOS is designed to identify, test, and configure
the system in preparation for starting the operating system. At the completion of POST, the PC
compatible system BIOS attempts to have all of the appropriate devices enabled in order for them to be
properly recognized and functioning when the operating system loads.
Over the years, PC compatible systems have become much more sophisticated in terms of the bus
architectures supported and the devices attached. As these PC compatible systems have evolved and
become more sophisticated, so has the system BIOS, which is responsible for the initial configuration of
these devices. However, one component has remained relatively constant in a PC compatible system. This
is the system resources. System resources, as described in this document include DMA channels,
Interrupt Request Lines (IRQs), I/O addresses, and memory.
As the sophistication of these systems increases with more and more devices, the possibility of resource
conflicts also increase, leading to a possible boot or system failure. The Plug and Play BIOS specification
is defined to solve the problems that occur with resource conflicts. Specifically, the Plug and Play BIOS is
taking on a new responsibility to ensure that the operating system is loaded with a conflict free set of
resources, as well as indicating to the operating system the resources that are currently used by
systemboard devices.
2.1 System BIOS POST Requirements
In order to achieve the goals of Plug and Play, the system BIOS POST is responsible for achieving the
requirements listed below:
•• Maintain ISA POST compatibility
The important issue of this broad requirement is that a Plug and Play system BIOS is responsible for
the same POST requirements of an existing PC compatible system BIOS. This document focuses only
on the enhancements necessary to a PC compatible system BIOS and assumes that the basic BIOS
POST initialization is still performed.