Outlook 2007: PST and OST files may be up to 20% larger after the February 24, 2009 Cumulative Update

Source: Microsoft Support

RAPID PUBLISHING ARTICLES PROVIDE INFORMATION DIRECTLY FROM WITHIN THE MICROSOFT SUPPORT ORGANIZATION. THE INFORMATION CONTAINED HEREIN IS CREATED IN RESPONSE TO EMERGING OR UNIQUE TOPICS, OR IS INTENDED SUPPLEMENT OTHER KNOWLEDGE BASE INFORMATION.

Important This article contains information about how to modify the registry. Make sure that you 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:

322756 (http://vkbexternal/VKBWebService/ViewContent.aspx?scid=kb;EN-US;322756&PortalId=1) How to back up and restore the registry in Windows XP and Windows Vista

 

 



After you install the February 24, 2009 cumulative update for Outlook 2007 you may see the file size of your .ost and .pst files grow by up to 20%.

The February 24, 2009 cumulative update for Outlook 2007 includes changes related to the general reading and writing characteristics of the .pst/.ost file so that less is demanded from your hard drive to perform the same general operations in Outlook. For instance, the file flushing process was optimized so that it interacts more efficiently with operating system and disk-write caches. There is also a change in the way new data is written to the .pst/.ost so that the data is saved much closer together on the physical disk. As a result, there is less physical work required from the drive, thereby speeding up the time it takes to write the same amount of data to the drive. However, a side-effect of this data writing algorithm is that .pst/.ost files will be about 20% larger than before the February 24, 2009 cumulative update.

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 the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.



If you do not want your .pst/.ost files to use this new process you can disable the feature by adding the following registry data to the Outlook client:

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST
DWORD: PreferCompactness
Values: 0 = (the default) new behavior
            1 = disable this new behavior

For additional information on the February 24, 2009 Cumulative Update for Outlook 2007, please see the following articles in the Microsoft Knowledge Base:

   961752           Description of the Outlook 2007 hotfix package (Outlook.msp): February 24, 2009

http://support.microsoft.com/default.aspx?scid=kb;EN-US;961752 (http://support.microsoft.com/default.aspx?scid=kb;en-us;961752)

   968009           Outlook 2007 improvements in the February 2009 cumulative update

http://support.microsoft.com/default.aspx?scid=kb;EN-US;968009 (http://support.microsoft.com/default.aspx?scid=kb;en-us;968009)

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