imported>SomethingForDeletion: Adding short description: "Legacy Plug and Play standard"

2025-01-19T03:42:46Z

Adding short description: "Legacy Plug and Play standard"

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{{Short description|Legacy Plug and Play standard}}
The '''Extended System Configuration Data''' ('''ESCD''') is a specification for configuring [[x86]] computers of the [[ISA PNP]] era. The specification was developed by [[Compaq]], [[Intel]] and [[Phoenix Technologies]]. It consists of a method for storing configuration information in [[nonvolatile BIOS memory]] and three [[BIOS]] functions for working with that data.<ref name="Shanley1995">{{cite book|author=Tom Shanley|title=Plug and Play System Architecture|url=https://archive.org/details/plugplaysystemar00mind|url-access=limited|year=1995|publisher=Addison-Wesley Professional|isbn=978-0-201-41013-6|page=[https://archive.org/details/plugplaysystemar00mind/page/n286 267]}}</ref><ref>Compaq Computer Corporation, Phoenix Technologies Ltd., Intel Corporation "[http://download.intel.com/support/motherboards/desktop/sb/pnpbiosspecificationv10a.pdf Plug and Play BIOS Specification]" Version 1.0A, May 5, 1994 (This details the ESCD BIOS functions, but it is not the actual ESCD format specification)</ref>

The ESCD data may at one time have been stored in the latter portion of the 128 byte extended bank of battery-backed CMOS RAM but eventually it became too large and so was moved to BIOS flash.<ref name="Brooks2003">{{cite book|author=Charles J. Brooks|title=A+ Certification Training Guide: (Exam 220-301, Exam 220-302)|url=https://books.google.com/books?id=KrE0GGzOQ6oC&pg=PA593|year=2003|publisher=Que Publishing|isbn=978-0-7897-3044-2|page=593}}</ref><ref name="Mueller2003">{{cite book|author=Scott Mueller|title=Upgrading and Repairing PCs|url=https://archive.org/details/upgradingrepairi00mue_qq3|url-access=registration|year=2003|publisher=Que Publishing|isbn=978-0-7897-2745-9|page=[https://archive.org/details/upgradingrepairi00mue_qq3/page/389 389]|edition=14th}}</ref>

It contains information about [[Industry Standard Architecture|ISA]] [[Legacy Plug and Play|PnP]] devices is stored. It is used by the [[BIOS]] to allocate resources for [[Computer hardware|device]]s like [[expansion card]]s. The ESCD data is stored using the data serialization format used for [[Extended Industry Standard Architecture|EISA]]. Its data starts with the "ACFG" signature in ASCII. PCI configuration can also be stored in ESCD, using virtual slots.<ref>[http://stuff.mit.edu/afs/sipb/contrib/doc/PnP/escd.ps ESCD specification 1.02A], Appendix A, pp. 21-22</ref> Typical storage usage for ESCD data is 2–4 KB

The BIOS also updates the ESCD each time the [[Computer hardware|hardware]] configuration changes, after deciding how to re-allocate resources like [[Interrupt request|IRQ]] and [[memory map]]ping ranges. After the ESCD has been updated, the decision need not be made again, which thereafter results in faster startup without conflicts until the next hardware configuration change.

== References ==
{{Reflist}}

== Further reading ==
* {{cite book|author1=James Kelsey|title=Programming Plug and Play|year=1995|publisher=Sams|isbn=978-0-672-30703-4}}

== External links ==
* [https://lkml.org/lkml/2001/7/8/47 ESCD Support for 2.4.6-ac1/PNPBIOS (was: reading/writing CMOS beyond 256 bytes?)]

[[Category:Motherboard]]
[[Category:BIOS]]

{{compu-hardware-stub}}

Extended System Configuration Data - Revision history

imported>SomethingForDeletion: Adding short description: "Legacy Plug and Play standard"