The sfc is an utility in Windows and stands for System File Checker. The sfc utility is primarily used when you suspect that some of system files in your Windows machine are corrupted. If sfc command with /scannow switch is run, it looks for altered or damaged protected system files and replaces the incorrect files by retrieving the correct version of that file from %systemroot%\system32\dllcache folder. Hence, it is very useful tool to repair Windows system files.
It was first introduced in Windows 98 and still available with Windows XP/ Vista/ 7 / 8 / 8.1 / 10. This command is run from the command prompt. It has many switches available but the one which is most common is /scannow. This switch basically scans all the Windows Protected System Files and replaces the incorrect protected system files with correct copy of the file from dllcache folder or from Windows CD. Some of the common switches are as follows along with the command syntax -
sfc [/scannow] [/scanonce] [/scanboot]
/scannow : It starts immediately and scans all protected system files
/scanonce : This is used to scan all protected files once only
/scanboot : This is used if you want to scan all the protected system files every time the computer is restarted
There are other paramaneters also which goes with it. I have just covered few basic once which are available in all Windows Version of OS. There are some parameters which was specific to particular version of Windows Operating System.
On Windows 8, 8.1 and 10, Deployment Image and Servicing Management (DISM) is used to fix component store corruption that causes issue with SFC and prevents it from working properly.
The command is run from Command Prompt with Administrator right. Open the CMD and type the command below:
DISM /Online /Cleanup-Image /RestoreHealth
Note: DISM tool isn't available with Windows 7 but, you could use "System Update Readiness Tool".