Microsoft KB Archive/816488

= You may experience memory performance issues on a Windows 2000-based computer that has multiple Intel Pentium 4 processors =

Article ID: 816488

Article Last Modified on 2/21/2007

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APPLIES TO


 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition
 * Microsoft Windows 2000 Server

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For a Microsoft Windows Server 2003 version of this article, see 897335.

Important This article contains information about how to modify the registry. Make sure to back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows registry



SYMPTOMS
On a Microsoft Windows 2000-based computer that has multiple Intel Pentium 4 processors, you may experience the following symptoms:
 * An unexpectedly slow startup time.
 * Memory performance issues.
 * CPU spikes in the system process that occur immediately after startup.



CAUSE
This problem may occur if the page zeroing thread is configured to use the extended memory manager interface (XMMI) instruction set.

When a process allocates virtual memory, the Windows memory manager will clear the virtual memory pages before the memory manager lets the requesting process access the pages. This step makes sure that a process cannot access data in virtual memory that was previously owned by another process.

The page zeroing thread that is responsible for cleaning used memory pages is configured to use one of two instruction sets early in the startup process. By default, the page zeroing thread is configured not to use the XMMI instruction set on Pentium 4 multiprocessor systems. This restriction exists because of hardware issues that cause a decrease in performance on many Pentium 4 multiprocessor systems. Under certain conditions, the XMMI instruction set is incorrectly selected. This issue may be more common on single processor virtual machines that run on multiprocessor hosts. A virtual machine may incorrectly select the zeroing loop because the virtual machine detects a single processor during startup on a multiprocessor host.



Hotfix information
A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that are experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

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

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

Prerequisites
To install this hotfix, you must be running Windows 2000 Service Pack 3 or Windows 2000 Service Pack 4. (SP4) For more information, click the following article number to view the article in the Microsoft Knowledge Base:

260910 How to obtain the latest Windows 2000 service pack

Restart requirement
You must restart the computer after you apply this hotfix.

Hotfix replacement information
This hotfix replaces the hotfix that was originally includedwith Windows 2000 SP4.

File information
The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.     Date         Time    Version          Size        File name --    10-Feb-2004  19:47   5.0.2195.6897      30,160    Mountmgr.sys 05-Apr-2004 20:39   5.0.2195.6921   1,700,928    Ntkrnlmp.exe 05-Apr-2004 20:39   5.0.2195.6921   1,700,608    Ntkrnlpa.exe 05-Apr-2004 20:39   5.0.2195.6921   1,722,176    Ntkrpamp.exe 05-Apr-2004 20:39   5.0.2195.6921   1,677,824    Ntoskrnl.exe



MORE INFORMATION
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

After you apply this hotfix, you must add and configure the XMMIZeroingEnable registry entry to disable XMMI-zeroing functionality. To do this, follow these steps:  Click Start, click Run, type regedit in the Open box, and then click OK.. Locate the following registry subkey:

 In the left pane, right-click kernel, point to New, and then click DWORD Value. Type XMMIZeroingEnable as the entry name, and then press ENTER. Right-click XMMIZeroingEnable, and then click Modify.</li> To disable XMMI-zeroing, type 2 in the Value data box, and then click OK.

Note To re-enable XMMI-zeroing, type 1 in the Value data box, and then click OK.</li> Quit Registry Editor.</li> Restart the computer.</li></ol>

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.

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STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.

Keywords: kbhotfixserver kbqfe kbwin2000sp5fix kbwin2000presp5fix kboswin2000fix kbfix kbbug KB816488

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