Microsoft KB Archive/813926

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Article ID: 813926

Article Last Modified on 1/9/2007


  • Microsoft Windows XP Home Edition
  • Microsoft Windows XP Service Pack 1a
  • Microsoft Windows XP Professional
  • Microsoft Windows XP Service Pack 1a


This article describes the differences between Windows XP Service Pack 1 (SP1) and Service Pack 1a (SP1a). Windows XP updates are distributed in service packs. You can use service packs to help keep Windows XP current and to extend and update the functionality of your computer. On September 9, 2002, Microsoft released Windows XP SP1. On February 3, 2003, Microsoft released SP1 again as SP1a.


If you are not running Windows XP SP1, install SP1a to make sure that you have the latest security and reliability updates for Windows XP. Install any appropriate security updates and hotfixes that are already released or that will be released after SP1 on Windows XP-based computers that are running SP1a. Windows Update will continue to offer the same set of updates for Windows XP-based computers that are running either SP1 or SP1a.

To determine if you are running Windows XP SP1, right-click My Computer, and then click Properties. If "Service Pack 1" appears under System, you are already running Windows XP SP1. There is no benefit to installing SP1a if you are already running Windows XP SP1. Microsoft does not recommend that you install SP1a if you are already running SP1.

Windows XP SP1a is the same as Windows XP SP1 except that the Microsoft virtual machine (VM) is removed in SP1a.

Technical Changes

  • Windows XP SP1a does not include or install the Microsoft VM, which provides support for running Java programs.

    Note If you are running Windows XP or Windows XP SP1 with the Microsoft VM, you can continue to update the Microsoft VM by using Windows Update. If you are running Windows XP without the Microsoft VM, you do not have to install updates to the Microsoft VM. Therefore, these updates are not offered to you when you visit Windows Update. Microsoft is no longer able to provide a download of the Microsoft VM for computers that do not already have the Microsoft VM installed. For more information, visit the following Microsoft Web site:

    To determine if you are running the Microsoft VM, follow these steps:

    1. Click Start, and then click Run.
    2. Type cmd, and then click OK.
    3. At the command prompt, type jview and then press ENTER.

      If you are not running the Microsoft VM, you receive the following error message:

      'jview' is not recognized as an internal or external command, operable program or batch file.

  • When you install Windows XP SP1a, the following changes are made to the registry. These changes indicate that SP1a is installed:
    • A string value is created in the following registry key and its value data is set to "a":

      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SubVersionNumber

    • The value data for the Description string value in the following registry key is updated to include "SP1a":

      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows XP\SP1\Q324720

  • The title for the Windows XP Service Pack 1 entry in the Add or Remove Programs tool in Control Panel is changed to "Windows XP Service Pack 1a."

    • You can use this entry to remove the service pack. It is present only if you choose to archive files when you install the service pack.
    • This entry is not updated if you use the Microsoft Software Installer package to install Windows XP SP1a.

Documentation Changes

  • The title for the SP1a Release Notes has been changed to include "SP1a" in most languages. In other places where "Service Pack 1" is used, the text has not been changed.

Note On the Microsoft Web site, "Service Pack 1" may be used in some cases to refer to either SP1 or SP1a.

There are no other changes or fixes included in this update. For additional information about what is fixed in SP1 and SP1a, and how to obtain SP1a, click the following article number to view the article in the Microsoft Knowledge Base:

322389 How to Obtain the Latest Windows XP Service Pack

Keywords: kberrmsg kbhowto kbregistry kbenv KB813926