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PC Knowledge Base - Windows Operating System Dllcache
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By default, all system files are cached in the cache folder, and the default size of the cache is 400 MB. Because of disk space considerations, it may not be desirable to maintain cached versions of all system files in the cache folder. To change the size of the cache, change the setting of the SFCQuota value in the following registry key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
WFP stores verified file versions in the Dllcache folder on the hard disk. The number of cached files is determined by the setting of the SFCQuota value (the default size is 0xFFFFFFFF, or 400 MB). The administrator can make the setting for the SFCQuota value as large or small as needed. Note that if you set the SFCQuota value to 0xFFFFFFFF, the WFP feature caches all protected system files (approximately 2,700 files).

There are two cases in which the cache folder may not contain copies of all protected files, regardless of the SFCQuota value:

Additionally, all drivers in the Driver.cab file are protected, but they are not populated in the Dllcache folder. WFP can restore these files from the Driver.cab file directly without prompting the user for the source media. However, running the sfc /scannow command does populate the files from the Driver.cab file into the Dllcache folder.

If WFP detects a file change and the affected file is not in the cache folder, WFP examines the version of the changed file that the operating system is currently using. If the file that is currently in use is the correct version, WFP copies that version of the file to the cache folder. If the file that is currently in use is not the correct version, or if the file is not cached in the cache folder, WFP tries to locate the installation source. If WFP cannot find the installation source, WFP prompts an administrator to insert the appropriate media to replace the file or the cached file version. The SFCDllCacheDir value (REG_EXPAND_SZ) in the following registry key specifies the location of the Dllcache folder.

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
The default value data for the SFCDllCacheDir value is %SystemRoot%\System32.
The SFCDllCacheDir value can be a local path. By default, the SFCDllCacheDir value is not listed in the
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
registry key. To modify the cache location, you must add this value.

When Windows starts up, WFP synchronizes (copies) the WFP settings from the following registry key

HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows NT\Windows File Protection
to the following registry key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
Therefore, if the SfcScan, SFCQuota, or SFCDllCacheDir values are present in the
HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows NT\Windows File Protection
subkey, the values take precedence over the same values in the
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon subkey.
For additional information about the System File Checker tool in Windows XP and Windows Server 2003, click the following article number to view the article in the Microsoft Knowledge Base: 310747 Description of Windows XP and Windows Server 2003 System File Checker (Sfc.exe) For additional information about the WFP feature, visit the following Microsoft Web site: http://msdn.microsoft.com/library/en-us/wfp/setup/windows_file_protection_start_page.asp For additional information about Windows Installer and WFP, visit the following Microsoft Web site: http://msdn.microsoft.com/library/en-us/msi/setup/windows_file_protection_on_windows_2000_and_windows_xp.asp

The above applies to:



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