How to Check System File Integrity (SFC)
A different layer from checking the disk itself: SFC checks whether Windows' own internal files are intact, and DISM is the follow-up when SFC's own repair copies are damaged too — with the fastest order to run them in.
Windows starts acting strange: programs that used to work now fail to open, error messages that make no sense, features that have simply stopped responding. Before thinking about reinstalling anything, it is worth checking whether the reason is that some internal Windows file has become damaged — and fixing it, in most cases, takes a single command.
This is not the same as checking the disk
If you already know our guide on how to check disk health, you may wonder how this differs. They are different layers: that one checks the physical disk itself (whether there are damaged sectors, whether the hardware is failing). SFC (System File Checker) checks something more specific: whether Windows' own internal files are intact or have become corrupted — the disk can be perfectly healthy and still have damaged system files.
The main command: SFC
Open Command Prompt as administrator (search for it, right-click, "Run as administrator") and type:
sfc /scannow
It will take several minutes. Do not close the window until it reaches 100%. When it finishes, you will see one of these messages:
| Message | What it means |
|---|---|
| Did not find any integrity violations | Everything is fine, this is not the issue |
| Found corrupt files and repaired them | Fixed — restart and check whether the original problem is gone |
| Found corrupt files but could not fix some of them | One more step is needed: DISM (see below) |
If SFC could not fix everything: DISM
SFC repairs using good copies stored within Windows itself. If those spare copies are ALSO damaged, SFC has nothing valid to pull a replacement from, no matter how hard it tries. That is where DISM comes in: it repairs that "reserve" of good copies, usually by downloading what is needed from Windows Update.
DISM /Online /Cleanup-Image /RestoreHealth
You will find guides that recommend running DISM before SFC, and others that say exactly the opposite — it is not that they contradict each other for no reason, it is that both orders are reasonable depending on the case. Running SFC first is faster and fixes most cases without needing anything more. If SFC cannot repair everything, running DISM and then repeating SFC fixes practically the rest. Starting with SFC is the simpler path, escalating to DISM only if needed.
After running DISM, repeat sfc /scannow once more —
now it should have good copies to draw from.
Warning: DISM needs an internet connection to download the replacement files from Windows Update. Without a connection, the command can fail or get stuck halfway through.
Could a virus be the reason for the damaged files?
It is possible, although it is not the most common cause — most cases come from sudden power cuts, interrupted updates or faults in the disk itself. Even so, if you notice other odd symptoms besides damaged files, it is worth ruling it out with our guide on how to remove viruses and malware from Windows before repeating the SFC/DISM process.
Worth keeping in mind: running SFC carries no risk to your personal files — it only acts on internal files of the operating system itself, never on your documents, photos or installed programs.
Frequently asked questions
What exactly is SFC?
The acronym for 'System File Checker', a tool included in Windows that checks whether the operating system's own internal files are intact, and repairs them automatically if it finds any damaged.
Is it the same as running an antivirus?
No. An antivirus looks for malicious programs; SFC looks for Windows' own files that have become damaged or modified, whatever the cause. They are complementary checks, not substitutes for one another.
What do I do if the command says it found errors but could not fix them all?
Run DISM /Online /Cleanup-Image /RestoreHealth and, once it finishes, repeat sfc /scannow once more. This second attempt usually completes the repair that was left half done.
How long does SFC take to finish?
Usually between 10 and 20 minutes, depending on your disk's speed and how many files it needs to check. DISM can take longer if it needs to download files from Windows Update.