System File Checker
A command-line utility called System File Checker (SFC.EXE) allows an Administrator to scan all protected files to verify their versions. System File Checker can also set the registry value SFCScan discussed in Additional Registry Settings later in this article.
System File Checker will also check and repopulate the %Systemroot%\system32\dllcache directory. If the dllcache directory becomes corrupted or unusable, SFC /SCANNOW, SFC /SCANONCE, SFC /SCANBOOT, or SFC /PURGECACHE can be used to repair the contents of the dllcache directory.
SFC.exe scans all protected system files and replaces incorrect versions with correct Microsoft versions. The following shows the syntax:
SFC [/SCANNOW] [/SCANONCE] [/SCANBOOT] [/CANCEL] [/QUIET] [/PURGECACHE] [/CACHESIZE=x]
/SCANNOW Scans all protected system files immediately.
/SCANONCE Scans all protected system files once.
/SCANBOOT Scans all protected system files at every boot.
/CANCEL Cancels all pending scans of protected system files.
/QUIET Replaces all incorrect file versions without prompting the user.
/PURGECACHE Purges the file cache and scans all protected system files immediately.
/CACHESIZE=x Sets the file cache size (in megabytes).