This article describes the prerequisite software updates that apply to versions of Windows Vista that are mentioned in the "Applies to" section. These updates are a prerequisite for Windows Vista Service Pack 1 (SP1). Additionally, these updates help improve reliability when you install or remove Windows Vista SP1.

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Two or three additional software updates are required before you install Windows Vista SP1. The software updates that are required depend on the version of Windows Vista that you want to upgrade. Prerequisite update 935509 that is listed in this article only applies to Windows Vista Enterprise and to Windows Vista Ultimate. The other prerequisite updates that are listed in this article apply to all versions of Windows Vista.

Before Windows Vista SP1 is released, these prerequisite updates will be delivered to most users through Windows Update as part of regularly scheduled monthly updates. These updates will be installed together with other updates that will require that you restart the computer. Therefore, an additional restart will not be required. This delivery method will help simplify installation of the required updates.

If you decide to install Windows Vista SP1 by using the stand-alone installer instead of by using Windows Update, you will not have to install the prerequisite updates separately. The prerequisite updates will be installed by the stand-alone installer if they are necessary. The following three updates are required before you install Windows Vista SP1. However, these updates are also recommended if you do not intend to install Windows Vista SP1. These updates help improve reliability and performance when you install future individual updates from Microsoft:

•	935509 (http://support.microsoft.com/kb/935509/) A software update is available for versions of Windows Vista that include the Windows BitLocker Drive Encryption feature Update 935509 lets you correctly service Windows BitLocker Drive Encryption-capable computers. This update only applies to the following versions of Windows Vista that include Windows BitLocker Drive Encryption: • Windows Vista Enterprise • Windows Vista Ultimate
•	Update 938371 updates Windows Vista in order to install or to remove Service Pack 1 more reliably. For more information, see the "Update information" section.
•	937287 (http://support.microsoft.com/kb/937287/) A software update is available for the Windows Vista installation software feature Update 937287 is a prerequisite package that contains updates to the Windows Vista installation software. The installation software is the component that handles the installation and removal of software updates, language packs, optional Windows features, and service packs. This update is necessary to successfully install and remove Windows Vista SP1 on all versions of Windows Vista. This update will be available on the Windows Update Web site soon after the release of update 935509 and before the release of Windows Vista SP1.

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Update information

The original release of Update 938371 updates several internal components that Windows Vista requires in order to install or to remove Windows Vista Service Pack 1 more reliably. This update must be applied separately before you install Windows Vista SP1 to make sure that Windows Vista SP1 can be installed or removed from the computer. Update 938371 is necessary to install and to remove Windows Vista SP1 on all versions of Windows Vista.

Update 938371 is available from the Windows Update Web site. To obtain this update, follow these steps:

1.	Click Start, click Control Panel, and then click Security.
2.	Under Windows Update, click Check for updates.

Prerequisites

No prerequisites are required.

Restart requirement

You must restart the computer after you apply this update.

Update replacement information

This update does not replace a previously released update.

Update removal information

You cannot remove this update.

Windows PE information

This software update does not apply to Windows Preinstallation Environment (Windows PE) for the release version of Windows Vista. Therefore, you cannot install Windows Vista SP1 in Windows PE for the release version of Windows Vista. If you want to run Windows PE for Windows Vista SP1, you must perform a clean installation of Windows PE for Windows SP1.

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

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