Editing Physical Address Extension (section)

== History ==

PAE was first implemented in the Intel [[Pentium Pro]] in 1995,<ref name="Shanley1998">{{cite book|author=T. Shanley|title=Pentium Pro and Pentium II System Architecture|url=https://books.google.com/books?id=MLJClvCYh34C&pg=PA439|year=1998|publisher=Addison-Wesley Professional|isbn=978-0-201-30973-7|page=439}}</ref> although the accompanying chipsets usually lacked support for the required extra address bits.<ref>{{cite web|url=https://learn.microsoft.com/en-us/previous-versions/windows/hardware/design/dn613969(v=vs.85) |title=Operating Systems and PAE Support |work=Hardware Developers Center |date=1 June 2017 |access-date=11 July 2023}}</ref>

PAE is supported by the Pentium Pro, [[Pentium II]], [[Pentium III]], and [[Pentium 4]] processors.  The first [[Pentium M]] family processors ("Banias") introduced in 2003 also support PAE; however, they do not show the PAE support flag in their [[CPUID]] information.<ref name="Pentium-M-PAE">{{cite web |url=https://help.ubuntu.com/community/PAE |title=PAE - Ubuntu Community Help Wiki}}</ref> This was remedied in a later revision of the "Dothan" core in 2005. It was also available on AMD processors including the AMD [[Athlon]]<ref>{{cite book|url=http://pdf.datasheetcatalog.com/datasheet/AdvancedMicroDevices/mXvyvs.pdf |access-date=2017-04-13|publisher=AMD, Inc.|title=AMD Athlon™ Processor x86 Code Optimization Guide|chapter=Appendix E|page=250 |date=February 2002|edition=Revision K|quote=A 2-bit index consisting of PCD and PWT bits of the page table entry is used to select one of four PAT register fields when PAE (page address extensions) is enabled, or when the PDE doesn’t describe a large page.}}</ref><ref>{{cite web|url=https://www.cpu-world.com/CPUs/K7/AMD-Athlon%20500%20-%20AMD-K7500MTR51B%20C.html |title=AMD Athlon 500 - AMD-K7500MTR51B C |work=Cpu-world.com |date=26 March 2014 |access-date=11 July 2023}}</ref> (although the chipsets are limited to 32-bit addressing<ref>{{cite web |url=http://pdf.datasheetcatalog.com/datasheet/AdvancedMicroDevices/mXvrtt.pdf |title=AMD-762 System Controller |page=2 |quote=Supports up to 4 Gbytes of memory}}</ref>) and later AMD processor models.

When [[Advanced Micro Devices|AMD]] defined their 64-bit extension of the industry standard [[x86]] architecture, [[x86-64|AMD64]] or x86-64, they also enhanced the paging system in "[[long mode]]" based on PAE.<ref name="amd-24593-PAE-REQ">{{cite web
  |url        = https://www.amd.com/system/files/TechDocs/24593.pdf
  |title      = Volume 2: System Programming
  |author     = AMD Corporation
  |date       = June 2023
  |work       = AMD64 Architecture Programmer's Manual
  |publisher  = AMD Corporation
  |access-date = 2023-07-11
  |page       = 139
  |quote=Long-mode page translation requires the use of physical-address extensions (PAE). Before activating long mode, PAE must be enabled by setting CR4.PAE to 1. Activating long mode before enabling PAE causes a general-protection exception (#GP) to occur.}}</ref> 
It supports 64-bit virtual addresses<ref name="amd-24593"/>{{rp|page=24|date=July 2023}} ({{as of|2023|7|lc=y|post=,}} 48 bits are implemented on some processors and 57 bits are implemented on others<ref name="amd-24593">{{cite web
  |url        = https://www.amd.com/system/files/TechDocs/24593.pdf
  |title      = Volume 2: System Programming
  |author     = AMD Corporation
  |date       = June 2023
  |work       = AMD64 Architecture Programmer's Manual
  |publisher  = AMD Corporation
  |access-date = 2023-07-11
  }}</ref>{{rp|pages=139,141–143|date=July 11, 2023}}<ref>{{cite web
  |url        = https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html
  |title      = Volume 3 (3A, 3B, 3C & 3D): System Programming Guide
  |at         = p. 4-7
  |date       = June 2023
  |work       = Intel 64 and IA-32 Architectures Software Developer’s Manual
  |publisher  = Intel
  |access-date = 2023-07-11
  }}</ref>), 52-bit physical addresses,<ref name="amd-24593"/>{{rp|page=24|date=December 2018}}
and includes [[NX bit]] functionality.
When the x86-64 processor is initialized, the PAE feature is required to be enabled before the processor is switched from Legacy Mode to Long Mode.<ref name="amd-24593-PAE-REQ"/>