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A20 line compatibility |
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==Versions==
Four versions of the PC System Design Guide were released. In PC-97, a distinction was made between the requirements of a ''Basic PC'', a ''Workstation PC'' and an ''Entertainment PC''. In PC-98, the ''Mobile PC'' was added as a category. In PC 2001, the ''Entertainment PC'' was dropped.
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Final version. First to require IO-[[Advanced Programmable Interrupt Controller|APIC]]s to be enabled on all desktop systems. Places a greatly increased emphasis on legacy-reduced and [[legacy-free PC|legacy-free]] systems. Some "legacy" items such as ISA expansion slots and device dependence on MS-DOS are forbidden entirely, while others are merely strongly discouraged.<ref>{{cite book|url=http://www.freeopenbook.com/pc-hardware-nutshell-3/pchardnut3-chp-1-sect-1.html |access-date=January 4, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110711032416/http://www.freeopenbook.com/pc-hardware-nutshell-3/pchardnut3-chp-1-sect-1.html |archive-date=July 11, 2011|isbn=0-596-00513-X|page=1.1 PCs Defined|edition=3rd|title=PC Hardware in a Nutshell|publisher=O'Reilly & Associates, Inc.|authors=Robert Bruce Thompson, Barbara Fritchman Thompson|date=24 July 2003 }}</ref>
PC 2001 removes compatibility for the [[A20 line]]: "If A20M# generation logic is still present in the system, this logic must be
terminated such that software writes to I/O port 92, bit 1, do not result in A20M# being asserted to the processor."<ref>{{cite book |url=https://www.tech-insider.org/windows/research/acrobat/001102/03sys-2001.pdf |publisher=Intel Corporation and Microsoft Corporation. |title=PC 2001 System Design Guide |chapter=Chapter 3 PC System |quote=SYS–0047. A20M# is always de-asserted (pulled high) at the processor |page=52 |access-date=2023-06-03 }}</ref>
== Color-coding scheme for connectors and ports ==
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