System File Checker Tool

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 the Dllcache 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.

Go to Start > Run, and type cmd in the Open box, then click OK to open a command prompt. Here you can using the command sfc with any of the switches indicated above (most of the time you’ll be using sfc /scannow (note the space after sfc).
When you start SFC, you may see the following prompt several times during the process:

What you can do to eliminate this is to copy the I386 folder from your Windows XP CD to your hard drive. Just copy the whole folder to your hard drive. Note that it’ll take some 500 MB in size, but with today’s large hard drive this shouldn’t be a problem. If you didn’t get a Windows CD when you purchased your computer, it is likely that this folder will already be on your hard drive.
The next step is to let Windows know where to find the files. Follow these steps:
1. Start the Registry Editor
2. Go to HKEY_LOCAL_MACHINE SOFTWARE Microsoft Windows CurrentVersion Setup
3. Double click the value SourcePath in the right pane, and enter the location where you copied the I386 folder (probably you copied the folder in the root of your C drive, thus the value would be C:.
4. Close the registry editor, and log off from Windows, or restart your computer for the setting to take effect.

Windows will keep track of updated system files that are introduced through the “normal” channels, such as Windows Update, Windows Service Pack installation using Update.exe, Hotfixes installed using Hotfix.exe or Update.exe and Operating system upgrades using Winnt32.exe.

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