In Windows XP we have more refined protection of these important files.
Windows File Protection
By default, Windows File Protection is always enabled and allows Windows digitally signed files to replace existing files safely. Currently, signed files are distributed through:
1. Windows Service Packs
2. Hotfix distributions
3. Operating system upgrades
4. Windows Update
5. Windows Device Manager
The main reason for using this utility is when you suspect there may be a problem with a Windows XP system file.
Perhaps you get a dialog box appear informing you of a problem with a .dll file, or your program will just not load! It is therefore worth checking to see if there are any corrupt system files using sfc scannow.
To do this simply go to the Run box on the Start Menu and type in:
This command will immediately initiate the Windows File Protection service to scan all protected files and verify their integrity, replacing any files which has a problem.
The following should appear to give an indication of how long the process is taking.
Any corrupt, missing or incorrect files would be replaced by this process. The most common issue with scannow sfc is the following dialog box appearing:
When does this happen?
In the computer's operating system registry, are several settings that are checked when you run scannow sfc.
The Windows File Protection service constantly monitors for any changes to the main system files.
Well Windows XP keeps a cache (copy) of these essential files at the following location:
C:WINDOWS\System32\Dllcache (assuming C: is your system root)
The dllcache folder is extremely important so Windows XP hides it from you! To view it go to:
My Computer--> Tools--> Folder Options--> View--> "uncheck" Hide protected operating system files.
If that's the case on your computer then there is normally no need for the original XP CD to be inserted as your computer has a "copy" it can get hold of in this cache.
But, if the Dllcache folder, or part of it, has become corrupted for some reason then you will be prompted for the XP CD - so your computer can get a clean copy.