AVG Signal Blog Performance Cleaning How to Repair Corrupted Windows System Files Using SFC or DISM

Written by Ivan Belcic
Published on January 14, 2021
Reviewed by Sandro Villinger

What is a Windows system file?

A Windows system file is any critical file related to your PC’s operating system (OS). System files are essential for your OS to work properly. In other words, system files are core files that keep Windows working the way it’s supposed to.

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    Over time, Windows system files may become corrupted. When that happens, Windows won’t be able to use them, and your PC performance can suffer. That’s why it’s so important to restore your Windows system files as soon as they get corrupted — because they inevitably will. 

    In this article, we’ll show you how to perform two different Windows 10 repair procedures as well as how to fix Windows 8 and Windows 7 system files.

    If you want to scan for and fix corrupted system files immediately with a Windows repair tool, skip down to our sections on repairing Windows system files using the System File Checker (SFC) tool or the DISM command.

    What does it mean if a Windows system file is corrupted?

    A corrupted file is one that has become unusable. This can happen suddenly and for a variety of reasons — more on that below. When normal files get corrupted, you won’t be able to open them. For example, you won’t be able to listen to a corrupted MP3 file or load a saved game from a corrupted save file. When you try to open a corrupted file, you’ll usually get an error message instead.

    Things get worse when system files become corrupted. Losing access to a particularly important system file can cause frequent Windows crashesthe blue screen of death — and Windows may even become completely unusable.

    How and why do files become corrupted?

    Files can become corrupted when you save or copy them, sometimes due to a bug or glitch in the software controlling the file. When a video game accidentally corrupts your save file, this is usually what’s happened. If the program realizes that there’s been an error, it will alert you and allow you to try and re-save or recreate that file. Otherwise, you may not find out until you try to open the file next time.

    Faulty software isn’t the only reason why shortcuts break in Windows and files get corrupted. Here are a few other reasons:

    • Computer crashes. Crashes can cause corrupt system files, and corrupt system files can cause crashes. It’s a vicious cycle.

    • Sudden power outages. If your computer’s power supply is unexpectedly cut off — if you unplug your desktop, or if your laptop’s battery dies — you may later discover that some of your files have been corrupted.

    • Power surges. If your computer’s power supply doesn’t regulate against power surges, a sudden rush of power can corrupt your system files. Use a surge protector to safeguard your computer.

    • Updating errors. There’s a chance that one or more of your system files may become corrupted by a bug when you’re updating Windows. This may also occur when installing or reinstalling Windows on your computer.

    • Malware. Viruses and other types of malware can corrupt system files as part of their attack strategy.

    • Hard disk problems. Issues in your hard disk — such as when it becomes packed with bloatware and other junk files — can result in files getting jumbled around and corrupted.

    You can address these issues with AVG TuneUp, a specialized computer optimization tool. Clean out your hard disk and reduce the risk of system crashes, update errors, and other common causes of corrupted files with one easy-to-use app.

    AVG TuneUp is a comprehensive performance booster that automatically keeps your computer running as efficiently and cleanly as possible. Plus, you can try it risk-free.

    How can you tell if a Windows system file is corrupted?

    A corrupted file doesn’t work the way it’s supposed to, and you generally won’t be able to open it. Since Windows system files are integral to your OS, any Windows errors — like the notorious blue screen — may be the result of a corrupted file.

    The Windows blue screen might be caused by corrupted Windows system files.Corrupted system files can cause the Windows blue screen of death.

    To check for corrupted files, compare a potentially corrupted file to another file of a similar type. Corrupted files can sometimes be much smaller than they’re supposed to be, so if you notice a significant size difference, corruption may be the cause.

    After identifying a potentially corrupted file, try replacing it with a clean copy. If your problems disappear, it’s likely because the original file was corrupted as well.

    How to scan and repair files using the System File Checker tool (SFC)

    The System File Checker (SFC) is a built-in Windows repair tool that scans your computer for corrupted Windows system files and attempts to restore any that it finds. To locate these troublesome files, use the SFC scannow command in the System File Checker. This easy Windows 10 repair tool is also available on Windows 8 and 7.

    Using the System File Checker on Windows 10, 8, and 7 is the same — the only difference is in how you open it. Here, we’ll show you how to repair Windows 10, 8, and 7 system files with the SFC scannow command.

    Opening the Command Prompt to run SFC scannow on Windows 10 and 7

    1. Open the Start menu and type the phrase cmd.

    2. Right-click Command Prompt from the results and select Run as Administrator.

      Opening the Command Prompt as an administrator in Windows 10
    3. Click Yes on the next screen to confirm.

      Choosing to allow Windows Command Processor to make changes to your device on Windows 10
    4. Check that the Command Prompt window has opened with administrative privileges by confirming that it says “Administrator” at the top of the window.

      The Command Prompt window in Windows 10

    From here, you’ll be ready to begin your Windows 10 repair. And if you’re using Windows 7, this tool will let you repair Windows 7 files as well. Skip ahead to begin running the SFC scannow command.

    Opening the Command Prompt to run SFC scannow on Windows 8 and 8.1

    1. Click the Windows icon in the lower-left corner to open the Start menu.

      The desktop in Windows 8.1, showing the location of the Start menu
    2. Click the magnifying glass in the upper-right corner to open the Search interface.

      The Start menu in Windows 8.1, showing the location of the Search icon
    3. Enter the search term command prompt, right-click on Command Prompt in the results, and select Run as administrator.

      Choosing to run Command Prompt as an administrator in Windows 8.1
    4. Click Yes to confirm.

      Choosing to allow Windows Command Processor to make changes to your device on Windows 8.1

    Running SFC scannow on Windows 10, 8, and 7

    Once you’ve opened the command prompt window, the next steps are the same on all versions of Windows. You can follow this process for Windows 10 repairs, or to repair Windows 7 and 8 system files.

    1. Enter the command sfc /scannow and press Enter. Wait until the scan is 100% complete, making sure not to close the Command Prompt window before then.

      Entering the command "sfc /scannow" in the Command Prompt window for Windows 10
    2. The results of the scan will depend on whether or not the SFC finds any corrupted files. There are four possible outcomes:

      • “Windows Resource Protection did not find any integrity violations.” This message means that your system files are fine.

      • “Windows Resource Protection could not perform the requested operation.” If Windows is having trouble, restart your computer in safe mode and try again.

      • “Windows Resource Protection found corrupt files and successfully repaired them.” This means that your corrupt files have been fixed. You’ll receive a link to the details of these repairs, should you wish to check exactly what happened. Restart Windows to complete the process.

      • “Windows Resource Protection found corrupt files but was unable to fix some of them.” This means that you have some corrupt system files, and you’ll need to do more work. Try restarting your computer in safe mode and running the sfc /scannow command again. You can also check the report details, then replace the corrupt files with healthy copies.

    For more detailed guidance, check Microsoft’s SFC support page. In our scan, several corrupted files were detected and repaired.

    The results of a successful "sfc /scannow" scan in Windows 10, showing that several corrupt files were detected and repairedIf this happens in your scan, super — your problems have been solved. Restart Windows and make sure everything is working properly.

    Alternatively, try the DISM command

    If the SFC isn’t working, try DISM. The DISM (Deployment Image Servicing and Management) tool uses Windows Update to restore corrupted system files. It’s available in newer versions of Windows, including Windows 10, 8, and 8.1. But you won’t be able to use DISM to repair Windows 7.

    Here’s how to use the DISM “Restore Health” command to fix your corrupted system files.

    1. Open the Command Prompt — if you’re not sure how, check the instructions above for Windows 10 or Windows 8 or 8.1.

      The Command Prompt window in Windows 10
    2. In the Command Prompt, type the command DISM.exe /Online /Cleanup-image /Restorehealth and press Enter to run the DISM tool.

      Running the DISM tool in Windows 10

    3. Allow the DISM tool to finish working before you close the Command Prompt window. This may take a few minutes.

      The Command Prompt in Windows 10, showing a completed DISM scan

    After the DISM scan is complete, restart your computer and try the SFC again.

    Prevent corrupted Windows system files

    If your Windows system files don’t become corrupted, you won’t have to worry about fixing them. Here’s how you can reduce the need for Windows 10 repair and keep older versions of Windows working properly.

    • Back up important files. If your files do get corrupted, you’ll have a clean copy ready to swap in.

    • Avoid malware. Many types of malware can corrupt your PC’s system files. A strong and reliable anti-malware tool can keep dangerous software off your computer and protect your files.

    • Shut down your computer properly. Don’t just pull the plug — use the shutdown procedure in the Start menu instead. Abrupt shutdowns can corrupt files.

    • Regularly maintain your hard drive. A failing or overcrowded hard drive is more likely to corrupt the files that it holds. Run the Windows CHKDSK utility from time to time to restore bad sectors on your drive.

    • Use specialized cleanup software. By keeping your computer clean and efficient, AVG TuneUp can reduce the risk of corrupted files. It’ll remove junk files and useless software and ensure your computer’s resources are always put to the best use.

    Clean and fix up your PC with AVG TuneUp

    Corrupted system files are a frequent symptom of a computer that’s too overburdened to work properly. This is where AVG TuneUp comes in — it’s an all-in-one performance optimizer that helps your computer make the most out of its available CPU power, memory, and storage space.

    By automatically cleaning out useless files, unwanted software, and everything else clogging up your computer, AVG TuneUp will ensure you have loads of space for valuable system files. And by focusing your computer’s attention only on the programs you need at any given time, you’ll never waste precious resources on memory-hogging background activities.

    The result? A PC that’s way less likely to wind up with the corrupted system files that brought you here in the first place. Try AVG TuneUp right now for free.

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    Ivan Belcic