A fix is available for three issues in the x2APIC mode in x64-based versions of Windows Server 2008 R2

After you install this hotfix, the x2APIC mode can be enabled on a computer that is running Windows Server 2008 R2, and the computer can support more than 255 processors.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must be running Windows Server 2008 R2.

Installation instructions

After you install this hotfix, use one of the following methods to enable the x2APIC mode on a computer that is running an x64-based version of Windows Server 2008 R2:

• Enable the "x2APIC" mode in BIOS firmware
  After you install this hotfix on a computer that is running an x64-based version of Windows Server 2008 R2, you can enable the x2APIC mode in BIOS, and then you can start the computer.
  
  Note If the x2APIC mode is enabled in BIOS, you cannot disable the x2APIC mode by using the options of the bcdedit command.
• Enable the "x2APIC" mode by using the options of the "bcdedit" command
  If you do not enable the x2APIC mode in BIOS, you have to use this method. The following are the commands that enable and disable the x2APIC mode:
  
  bcdedit /set x2apicpolicy enable
  
  
  bcdedit /set x2apicpolicy disable

Registry information

To use the hotfix in this package, you do not have to make any changes to the registry.

Restart requirement

You may have to restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

File information

The English (United States) version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and the times for these files are listed in Coordinated Universal Time (UTC). The dates and the times for these files on your local computer are displayed in your local time together with your current daylight saving time (DST) bias. Additionally, the dates and the times may change when you perform certain operations on the files.

Windows Server 2008 R2 file information notes

Important Windows 7 hotfixes and Windows Server 2008 R2 hotfixes are included in the same packages. However, hotfixes on the Hotfix Request page are listed under both operating systems. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under "Windows 7/Windows Server 2008 R2" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system that each hotfix applies to.

• The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table:
  

  Version	Product	Milestone	Service branch
  6.1.760 0.20xxx	Windows 7 and Windows Server 2008 R2	RTM	LDR

• The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows Server 2008 R2" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are extremely important to maintain the state of the updated components. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

For all supported x64-based versions of Windows Server 2008 R2