When you access a SATA device that supports the Native Command Queuing (NCQ) feature in Windows Vista or in Windows Server 2008, you may experience poor performance

On a Windows Vista-based or Windows Server 2008-based computer, you have a Serial Advanced Technology Attachment (SATA) device that supports the Native Command Queuing (NCQ) feature. However, you may experience poor performance when you access the SATA device.

This problem occurs if the computer uses the Microsoft AHCI driver (Msahci.sys). The SATA device supports queue depths of greater than 1 and less than 32. However, the Microsoft AHCI driver incorrectly sets the queue depth on the SATA device. In this case, NCQ is disabled for the SATA device.

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: 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.

Important Windows Vista and Windows Server 2008 hotfixes are included in the same packages. However, only one of these products may be listed on the “Hotfix Request” page. To request the hotfix package that applies to both Windows Vista and Windows Server 2008, just select the product that is listed on the page.

Prerequisites

To apply this hotfix on a Windows Vista-based computer, you must have Windows Vista SP1 installed. For more information, click the following article number to view the article in the Microsoft Knowledge Base: No prerequisites are required for Windows Server 2008-based computers.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

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 item in Control Panel.

Windows Vista and Windows Server 2008 file information notes

The MANIFEST files (.manifest) and MUM files (.mum) installed for each environment are listed separately. MUM and MANIFEST files, and the associated security catalog (.cat) files, are critical to maintaining the state of the updated component. The security catalog files (attributes not listed) are signed with a Microsoft digital signature.

For all supported 32-bit versions of Windows Server 2008 and of Windows Vista

For all supported 64-bit versions of Windows Server 2008 and of Windows Vista

For all supported Itanium-based versions of Windows Server 2008

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

For more information about NCQ, visit the following Web site:For more information about SSD, visit the following Web site:

Additional file information for Windows Server 2008 and for Windows Vista

Additional files for all supported 32-bit versions of Windows Server 2008 and of Windows Vista

Additional files for all supported 64-bit versions of Windows Server 2008 and of Windows Vista

Additional files for all supported Itanium-based versions of Windows Server 2008