Performance decreases in Windows Server 2008 R2 when the Hyper-V role is installed on a computer that uses Intel Westmere or Sandy Bridge processors

Applies to: Windows Server 2008 R2 StandardWindows Server 2008 R2 EnterpriseWindows Server 2008 R2 Datacenter More


Consider the following scenario:
  • You have a Windows Server 2008 R2-based computer that has a large amount of physical memory and that has Intel Westmere or Sandy Bridge processors.

    For example, you have a computer that has Intel Xeon 5600 series processors and that has 48 gigabytes (GB) physical memory.
  • You install the Hyper-V role on the computer.
In this scenario, the performance of the computer may decrease.

For example, the following performance issues may be encountered:
  • The CPU usage is high and the server responds slowly when you copy large files on the computer. For example, you copy a 10-GB file.
  • The disk I/O performance of the virtual machines (VMs) is slow.
  • Windows takes a long time to start.


This issue occurs because the hypervisor supports only eight variable range Memory Type Range Registers (MTRRs). Additionally, the hypervisor cannot access the additional variable MTRRs that are introduced on recent Intel processors. Therefore, some regions of system memory are set to the default Uncacheable memory type, and the performance of the computer significantly decreases.


  • MTRRs are processor model specific registers (MSRs) that control the default caching for ranges of physical memory.
  • Intel Westmere and Sandy Bridge processors introduce additional variable MTRRs to enable systems to use a large amount of memory.


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 this specific problem.

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, submit a request to 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: 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.


To apply this hotfix, you must be running one of the following operating systems:
  • Windows Server 2008 R2
  • Windows Server 2008 R2 Service Pack 1 (SP1)
For more information about how to obtain a Windows Server 2008 R2 service pack, click the following article number to view the article in the Microsoft Knowledge Base:

976932 Information about Service Pack 1 for Windows 7 and for Windows Server 2008 R2

Registry information

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

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

File information

The global 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, SR_Level (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table.
    VersionProductSR_LevelService branch
    Windows Server 2008 R2RTMGDR
    Windows Server 2008 R2RTMLDR
    Windows Server 2008 R2SP1GDR
    Windows Server 2008 R2SP1LDR
  • 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 Windows Server 2008 R2
File nameFile versionFile sizeDateTimePlatform


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Additional file information

Additional file information for Windows Server 2008 R2

Additional files for all supported x64-based versions of Windows Server 2008 R2
File nameAmd64_67bea49f4b337c102608760a878b0956_31bf3856ad364e35_6.1.7601.17592_none_37ff42790a6900fc.manifest
File versionNot applicable
File size710
Date (UTC)11-Apr-2011
Time (UTC)13:43
File nameAmd64_8a985f70d154980c200f4714ce9a3670_31bf3856ad364e35_6.1.7601.21701_none_5cef43c038bc80a3.manifest
File versionNot applicable
File size710
Date (UTC)11-Apr-2011
Time (UTC)13:43
File nameAmd64_cb3eff84ee36faec73c2de3df99ba685_31bf3856ad364e35_6.1.7600.20941_none_cc421777b5a99a2d.manifest
File versionNot applicable
File size710
Date (UTC)11-Apr-2011
Time (UTC)13:43
File nameAmd64_d2ca5366b0c74046153c25be7091bc18_31bf3856ad364e35_6.1.7600.16792_none_fc40bac5b638e541.manifest
File versionNot applicable
File size710
Date (UTC)11-Apr-2011
Time (UTC)13:43
File nameAmd64_microsoft-hyper-v-drivers-hypervisor_31bf3856ad364e35_6.1.7600.16792_none_8c387bd67f4112e6.manifest
File versionNot applicable
File size4,163
Date (UTC)09-Apr-2011
Time (UTC)07:27
File nameAmd64_microsoft-hyper-v-drivers-hypervisor_31bf3856ad364e35_6.1.7600.20941_none_8cf729d998370acb.manifest
File versionNot applicable
File size4,163
Time (UTC)07:38
File nameAmd64_microsoft-hyper-v-drivers-hypervisor_31bf3856ad364e35_6.1.7601.17592_none_8e1ed8dc7c677ed2.manifest
File versionNot applicable
File size4,163
Date (UTC)09-Apr-2011
Time (UTC)07:26
File nameAmd64_microsoft-hyper-v-drivers-hypervisor_31bf3856ad364e35_6.1.7601.21701_none_8f08c68f953d06f3.manifest
File versionNot applicable
File size4,163
Date (UTC)09-Apr-2011
Time (UTC)07:12