What Check Disk does and when to run it
Check Disk is a built-in tool that scans your hard drive for errors — bad sectors, corrupted files, and lost data fragments — and repairs them automatically. You run it when your computer is slow, freezing, or showing signs of disk problems, or as routine maintenance once or twice a year.
On Windows, the tool is called chkdsk (short for "check disk"). On Mac, it's Disk Utility. Both do the same job: they find problems your operating system missed and fix them before they cause data loss or crashes. The scan takes anywhere from a few minutes to several hours depending on your drive size and how many errors exist.
You do not need to run Check Disk constantly. If your computer is working normally, once or twice yearly is enough. Run it sooner if you notice stuttering, unexpected shutdowns, files that won't open, or if Windows shows a notification that your drive needs checking.
Key Takeaways
- On Windows, open Command Prompt as administrator, type chkdsk C: /F, and restart your computer to let the scan run before Windows loads.
- On Mac, open Disk Utility from Applications > Utilities, select your drive, and click First Aid to scan and repair.
- Check Disk requires a restart on Windows and will not run while your operating system is active, so schedule it when you can leave your computer alone for an hour or more.
- Back up your important files before running Check Disk, especially if your drive is showing signs of failure.
- If Check Disk finds errors it cannot repair, your drive may be failing and you should replace it soon.
How to run Check Disk on Windows 10 and 11
The fastest way is through Command Prompt. Press the Windows key, type cmd, right-click on Command Prompt, and select "Run as administrator." You must run it as administrator or the command will not work.
At the command prompt, type chkdsk C: /F (replace C with your drive letter if you want to check a different drive). The /F flag tells it to fix errors it finds. Press Enter. Windows will tell you it cannot run the scan right now because the drive is in use, and ask if you want to schedule it for the next restart. Type Y and press Enter.
Restart your computer. Before Windows loads, Check Disk will run automatically. You will see a black screen with white text showing the scan progress. Do not interrupt it — let it finish completely, even if it takes an hour. When it is done, your computer will boot normally.
If you want to check a drive other than your main Windows drive (like an external hard drive or USB stick), you can run the scan without restarting. Plug in the external drive, open Command Prompt as administrator, type chkdsk E: /F (using the correct drive letter), and press Enter. The scan will run while you wait.
How to run Check Disk on Mac
Open Finder, go to Applications, then Utilities, and double-click Disk Utility. In the left sidebar, you will see a list of all your drives. Click the drive you want to check (usually "Macintosh HD" for your main drive).
Click the "First Aid" button at the top of the window. A dialog will appear asking if you want to run the scan. Click "Run." Disk Utility will scan your drive and repair any errors it finds. You can use your Mac while this happens — you do not need to restart.
When the scan is complete, Disk Utility will show you a summary of what it found and fixed. If it says "The volume appears to be OK," your drive is healthy. If it found and repaired errors, your drive is working again but may have had problems. If it says it found errors it could not repair, your drive may be failing.
What to do if Check Disk finds errors it cannot fix
If Check Disk reports that it found errors but could not repair them, your hard drive is likely failing. This is not a problem you can solve by running the tool again — the damage is physical or the file system is too corrupted to recover.
Back up your files immediately to an external drive or cloud storage. Do not wait. A failing drive can stop working without warning. Once your files are safe, you should replace the drive. On a laptop, this usually means taking it to a repair shop. On a desktop, you can buy a replacement drive and install it yourself, or have a technician do it.
If your computer is still under warranty, contact the manufacturer before replacing the drive — they may cover it at no cost.
Understanding Check Disk options and what they mean
When you type a chkdsk command on Windows, you can add different flags to change what it does. The most common ones are:
- /F — Fixes errors found on the drive. You almost always want this.
- /R — Locates bad sectors and recovers readable information. This is slower than /F and is only needed if you suspect physical damage to the drive.
- /V — Shows a detailed list of every file being checked. Useful for troubleshooting but makes the scan slower.
- /X — Forces the drive to unmount before checking (Windows only). Use this if the drive is locked by another program.
For most people, chkdsk C: /F is all you need. If you want to be thorough, chkdsk C: /F /R will do a deeper scan, but it takes much longer — sometimes several hours on a large drive.
On Mac, Disk Utility does not have these options. First Aid automatically does what it can to repair your drive. If you want more detailed information, you can open Terminal (in Applications > Utilities) and type diskutil verifyVolume /, but for most users Disk Utility's First Aid button is enough.
How long Check Disk takes and what to expect
On a healthy drive with no errors, Check Disk usually finishes in 5 to 15 minutes. On a drive with errors, or a very large drive, it can take 30 minutes to several hours. A 1 TB drive with significant corruption might take 2 to 4 hours.
While Check Disk is running on Windows, you will see a progress bar and a percentage complete. The percentage does not move smoothly — it may stay at the same number for a while, then jump forward. This is normal. Do not restart your computer or unplug it while the scan is running, or you may damage your drive further.
On Mac, Disk Utility shows a progress bar and tells you what stage of the scan it is on. You can use your computer normally while it runs in the background, though your drive will be slower.
When to run Check Disk as routine maintenance
If your computer is working well, run Check Disk once or twice a year as preventive maintenance. Many people do this in spring and fall, or at the start and middle of the year. Pick a time when you can leave your computer on overnight, since the scan on Windows requires a restart and may take several hours.
You do not need to run it more often than that unless you notice problems. Running it too frequently will not help — it only finds and fixes errors that already exist. If your drive is healthy, repeated scans will just waste time.
If you use your computer heavily — for video editing, large file transfers, or running many programs at once — you might run Check Disk three or four times a year instead. Heavy use creates more wear on the drive and increases the chance of errors.
Frequently Asked Questions
Can I use my computer while Check Disk is running?
On Windows, no — Check Disk runs before Windows loads, so your computer is not usable. On Mac, yes — Disk Utility's First Aid runs in the background and you can use your Mac normally, though it will be slower.
What does "bad sector" mean?
A bad sector is a small area of your hard drive that cannot store data reliably. It might be caused by physical damage, age, or manufacturing defects. Check Disk finds these areas and marks them so your operating system will not try to use them.
Will Check Disk delete my files?
No. Check Disk repairs corrupted files and recovers lost data fragments, but it does not delete anything. If a file is too damaged to repair, Check Disk moves it to a folder called "Found" so you can decide what to do with it.
Do I need to run Check Disk if my computer is working fine?
Not urgently, but running it once or twice a year as maintenance is a good idea. It catches small problems before they become big ones. If your computer is working well, there is no rush — you can schedule it whenever is convenient.
What if Check Disk gets stuck and does not finish?
On Windows, wait at least two hours before assuming it is stuck — large drives can take a very long time. If it truly appears frozen (no progress for several hours), restart your computer and try again. On Mac, force-quit Disk Utility and try First Aid again. If the problem repeats, your drive may be failing.