The System File Checker (SFC) tool is a command-line tool that can be used to restore protected system files on your computer by using the backup versions that are stored in theDllcache folder, or files copied from the Windows XP installation source.

Protected file types include those with .sys, .dll, .exe, .ttf, .fon and .ocx file name extensions.

You must be logged on as an administrator or as a member of the Administrators group to be allowed to run System File Checker.

System File Checker Tool Syntax

/Scannow: Scans all protected system files immediately and replaces incorrect versions with correct Microsoft versions. This command may require access to the Windows installation source files.

/Scanonce: Scans all protected system files one time when you restart your computer. This command may require access to the Windows installation source files when you restart the computer.

/Scanboot: Scans all protected system files every time you start your computer. This command may require access to the Windows installation source files every time you start your computer.

/Revert: Returns SFC to the default setting (do not scan protected files when you start the computer). The default cache size is not reset when you run this command.

/Purgecache: Purges the file cache and scans all protected system files immediately. This command may require access to the Windows installation source files.

/Cachesize=x: Sets the file cache size to x megabytes (MB). The default size of the cache is 50 MB. This command requires you to restart the computer, and then run the /purgecache command to adjust the size of the on-disk cache.

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