Keeping Windows System Files in Check with SFC

Windows XP provides a command-line tool known as the System File Checker (sfc.exe) that allows you to control a variety of settings relating to WFP that would otherwise need to be changed manually via the Registry. As with any XP setting, using a provided tool is always better than editing the Registry manually, if only to avoid potential configuration errors.

The core function of SFC is to scan XP’s protected system files, and replace them with the correct versions (whether from cache or CD) as necessary. Futhermore, SFC will also repopulate the contents of the system file cache. This tool includes 6 main switches:
/scannow – forces an immediate scan of all system files, replacing files from cached versions and the XP CD.

/scanonce – forces a scan of all system files the next time your system reboots only.

/scanboot – forces a scan of all system files every time your system reboots.

/revert – resets WFP to its default configuration settings.

/purgecache – purges the contents of the system file cache, and then performs a scan of system files. This option is useful if you believe that the contents of the cache have become corrupt

/cachesize=x – configures a size to allocate to the system file cache, in MB. By default, there are no limits on the maximum cache size, although available disk space does have an impact.

In most cases, you’ll probably want to avoid the sfc /scanboot command, since it will negatively impact the time involved with each and every reboot. A better bet is to use the sfc /scanonce command as part of your regular monthly system maintenance, or sfc /scannow if you want to avoid the reboot.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.