Editing Physical Address Extension (section)

=== Microsoft Windows ===

32-bit versions of [[Microsoft Windows]] support PAE if booted with the appropriate option. According to Microsoft Technical Fellow [[Mark Russinovich]], some drivers were found to be unstable when encountering physical addresses above 4GB.<ref name="markr200807">{{cite web
|url=http://blogs.technet.com/markrussinovich/archive/2008/07/21/3092070.aspx
|title=Pushing the Limits of Windows: Physical Memory
|date=2008-07-21
|access-date=2010-07-11
|author=Mark Russinovich
|archive-url=https://web.archive.org/web/20080725002837/http://blogs.technet.com/markrussinovich/archive/2008/07/21/3092070.aspx
|archive-date=2008-07-25
|url-status=dead
}}</ref>

The following table shows the memory limits for 32-bit versions of Microsoft Windows:
{| class="wikitable sortable"
|+ Memory limits on 32-bit editions of Microsoft Windows,<br/>with PAE support<ref>{{cite web|title = Memory Limits for Windows releases|website = [[MSDN]]|publisher = [[Microsoft]]|date = December 5, 2007|url = http://msdn2.microsoft.com/en-us/library/aa366778.aspx|access-date = 2015-11-16|archive-url = https://web.archive.org/web/20071217093949/http://msdn2.microsoft.com/en-us/library/aa366778.aspx|archive-date = December 17, 2007|url-status = dead}}</ref><ref>{{cite web |title = Intel Physical Addressing Extensions (PAE) in Windows 2000 |website=Support |publisher = [[Microsoft]] |date = October 26, 2007 |url = http://support.microsoft.com/kb/268363/ |access-date = 2007-12-29 |archive-url=https://web.archive.org/web/20080101144938/http://support.microsoft.com/kb/268363/ |archive-date=2008-01-01 |url-status=dead}}</ref><ref>{{cite web |title = Overview of Windows Server 2003 R2 Datacenter Edition |website=[[Microsoft TechNet|TechNet]] |publisher = [[Microsoft]] |url = https://technet.microsoft.com/en-au/windowsserver/bb429508.aspx |access-date = 2009-05-15 |archive-url=https://web.archive.org/web/20111128004758/https://technet.microsoft.com/en-au/windowsserver/bb429508.aspx |archive-date=2011-11-28 |url-status=dead}}</ref>
! Windows version
! data-sort-type=number | Memory limit
|-
| [[Windows 2000]] Professional, Server
| style="text-align:right;" |  4 GB
|-
| [[Windows 2000]] Advanced Server
| style="text-align:right;" |  8 GB
|-
| [[Windows 2000]] Datacenter
| style="text-align:right;" |  32 GB
|-
| [[Windows XP]] Starter
| style="text-align:right;" |  512 MB
|-
| [[Windows XP]] (other editions)
| style="text-align:right;" |  4 GB
|-
| [[Windows Server 2003]] Web SP2
| style="text-align:right;" |  2 GB
|-
| [[Windows Server 2003]] Standard SP2
| style="text-align:right;" |  4 GB
|-
| [[Windows Server 2003]] Enterprise/Datacenter SP2
| style="text-align:right;" |  64 GB
|-
| [[Windows Storage Server|Windows Storage Server 2003]] Enterprise
| style="text-align:right;" |  8 GB
|-
| [[Windows Storage Server|Windows Storage Server 2003]] (other editions)
| style="text-align:right;" |  4 GB
|-
| [[Windows Home Server]]
| style="text-align:right;" |  4 GB
|-
| [[Windows Vista]] Starter
| style="text-align:right;" |  1 GB
|-
| [[Windows Vista]] (other editions)
| style="text-align:right;" |  4 GB
|-
| [[Windows Server 2008]] Standard, Web
| style="text-align:right;" |  4 GB
|-
| [[Windows Server 2008]] Enterprise, Datacenter
| style="text-align:right;" |  64 GB
|-
| [[Windows 7]] Starter
| style="text-align:right;" |  2 GB
|-
| [[Windows 7]] (other editions)
| style="text-align:right;" |  4 GB
|-
| [[Windows 8]] (all editions)
| style="text-align:right;" |  4 GB
|-
|[[Windows 10]] (all editions)
| style="text-align:right;" |  4 GB
|}

The original releases of Windows XP and Windows XP SP1 used PAE mode to allow RAM to extend beyond the 4&nbsp;GB address limit. However, it led to compatibility problems with 3rd party drivers which led Microsoft to remove this capability in Windows XP Service Pack 2. Windows XP SP2 and later, by default, on processors with the [[NX bit|no-execute (NX)]] or [[NX bit|execute-disable (XD)]] feature, runs in PAE mode in order to allow NX.<ref>{{cite web |url=http://support.microsoft.com/kb/888137 |title=The RAM reported by the System Properties dialog box and the System Information tool is less than you expect in Windows Vista or in Windows XP Service Pack 2 or later version (MSKB 888137) |access-date=2009-01-30 |work=Knowledge Base |publisher=Microsoft |archive-url=https://web.archive.org/web/20090204015716/http://support.microsoft.com/kb/888137 |archive-date=2009-02-04 |url-status=dead}}</ref> The NX bit resides in bit&nbsp;63 of the page table entry and, without PAE, page table entries on 32-bit systems have only 32&nbsp;bits; therefore PAE mode is required in order to exploit  the NX feature. However, "client" versions of 32-bit Windows (Windows XP SP2 and later, Windows Vista, Windows 7) limit physical address space to the first 4&nbsp;GB for driver compatibility <ref name="markr200807"/> even though these versions do run in PAE mode if NX support is enabled.

[[Windows 8]] and later releases will only run on processors which support PAE, in addition to [[NX bit|NX]] and [[SSE2]].<ref>{{cite web|last=Khurshid |first=Usman |url=http://www.technize.net/how-to-check-if-your-processor-supports-pae-nx-and-sse2-for-windows-8-installation/?ModPagespeed=noscript |title=How To Check If Your Processor Supports PAE, NX And SSE2 For Windows 8 Installation |work=technize.net |publisher=Technize |date=2 November 2012 |access-date=20 April 2014}}</ref><ref>{{cite web|url=https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-8.1-and-8/dn482072(v=win.10)|title=PAE/NX/SSE2 Support Requirement Guide for Windows 8|publisher=Microsoft Docs|date=10 February 2014|access-date=11 July 2023}}</ref>