What a check disc does and when to run one
A check disc (or disk check) is a built-in tool that scans your hard drive for errors and bad sectors — physical damage or corrupted data that can slow your computer or cause files to disappear. Running one tells you whether your drive has problems and, in many cases, fixes them automatically.
You should run a check disc if your computer is freezing, taking much longer than usual to start up, files are vanishing, or you see error messages about corrupted data. You may also want to run one after a crash or power failure, since those events can damage files on disk.
The process is different on Windows and Mac, and on Windows it depends on which version you have. Both tools require you to restart your computer, and both can take anywhere from a few minutes to several hours depending on your drive size and how many errors exist.
Key Takeaways
- Windows 11 and 10 use a tool called Check Disk (chkdsk) that you can start from Settings without restarting, though a full scan requires a restart.
- Mac uses Disk Utility, which you access by restarting into Recovery Mode and is the standard way to check for drive problems on Apple computers.
- A check disc scan can take several hours on a large drive, so plan to run it when you do not need your computer.
- If the scan finds errors, the tool will usually fix them automatically, but you should back up important files first in case something goes wrong.
How to run Check Disk on Windows 11 and Windows 10
The easiest way to start a check disc scan on Windows is through Settings. Open Settings, go to System, then Storage. Scroll down and click Repair storage sense or look for a Scan or Check now button. Windows will scan your drive in the background without restarting.
For a more thorough scan that fixes errors, you can use the command line. Press Windows key + R, type cmd, and press Enter. Type chkdsk C: /F (replace C with your drive letter if different) and press Enter. Windows will ask if you want to schedule the scan for the next restart — type Y and restart your computer. The scan will run before Windows starts up, which takes longer but is more complete.
If you want to see detailed information about what the scan finds, use chkdsk C: /F /V instead. The /V flag shows every file the tool checks. On very large drives, this can produce a lot of text, so you may want to skip it unless you are troubleshooting a specific problem.
How to run Disk Utility on Mac
On Mac, the equivalent tool is Disk Utility, and you access it by restarting into Recovery Mode. Restart your Mac and hold down Command + R as it starts up. Keep holding until you see the Apple logo or a spinning globe. This takes you to Recovery Mode, where you will see a menu of tools.
Click Utilities in the menu bar, then select Disk Utility. In the left sidebar, click your main drive (usually called "Macintosh HD" or similar). Click the First Aid button at the top. Disk Utility will scan your drive and repair errors automatically. This process can take 10 minutes to an hour depending on your drive size.
When the scan finishes, you will see a message saying the drive is okay or describing what was repaired. Click Done, then close Disk Utility. Click the Apple menu in the top left and select Restart to exit Recovery Mode and go back to your normal Mac desktop.
What to do before running a check disc
Before you start a scan, back up any files you cannot afford to lose. While check disc tools are designed to fix problems without destroying data, errors during the repair process are rare but possible. If you have important documents, photos, or other files, copy them to an external drive or cloud storage first.
Close all open programs and save any work in progress. On Windows, you can run a quick scan while using your computer, but a full scan with the /F flag requires a restart and will interrupt anything you are doing. On Mac, you must restart into Recovery Mode, so plan accordingly.
If your computer is very slow or freezing frequently, you may want to run the check disc scan during a time when you do not need the machine — overnight or over a weekend. A full scan on a large drive can take 8 to 12 hours.
Understanding check disc results
When the scan finishes, you will see a summary of what was found. On Windows, the command line will show the number of bytes in bad sectors and how many files were repaired. On Mac, Disk Utility will display a message like "The volume Macintosh HD appears to be OK" or list specific issues that were fixed.
If the tool reports that your drive is okay, you can stop worrying — there are no errors to fix. If it found and repaired errors, your computer should run more smoothly after the next restart. If it found errors but could not repair them, or if it reports the same errors after running the scan again, your drive may be failing and you should consider replacing it soon.
Keep in mind that a check disc scan only finds problems with the drive itself, not with software or settings that might be slowing your computer down. If your machine is still slow after the scan, the issue may be too many programs running at startup, insufficient memory, or malware.
When to replace your drive instead of repairing it
If check disc finds errors on the same sectors repeatedly, or if the scan takes much longer than expected (more than 24 hours on a modern drive), your drive is probably failing. In that case, running more scans will not help — you should back up your files and replace the drive.
Similarly, if your computer is making clicking, beeping, or grinding sounds while the scan runs, that is a sign of physical damage. Stop the scan immediately, back up your data, and take the computer to a repair shop or replace the drive yourself if you are comfortable doing so.
A failing drive can sometimes be used for a few more weeks or months, but it will get worse over time. The sooner you replace it, the less risk you run of losing files permanently.
Frequently Asked Questions
How long does a check disc scan take?
A quick scan usually takes 5 to 15 minutes. A full scan with error repair can take anywhere from 30 minutes to 12 hours depending on your drive size, how fragmented it is, and how many errors exist. Larger drives and drives with many errors take longer.
Can I use my computer while a check disc scan is running?
On Windows, you can use your computer during a quick scan from Settings. During a full scan started from the command line with the /F flag, your computer must restart and you cannot use it. On Mac, you must restart into Recovery Mode, so your computer is not available during the scan.
What does it mean if check disc finds bad sectors?
Bad sectors are areas of your drive that are physically damaged or corrupted. Check disc marks them so your computer will not try to store data there. If the tool finds and repairs bad sectors, your drive will work normally, but it has less usable space. If bad sectors keep appearing, your drive is failing.
Do I need to run check disc regularly?
You do not need to run it on a schedule. Run a check disc scan only when you notice problems like freezing, slow startup, or error messages. If your computer is working normally, there is no benefit to scanning regularly.
What if check disc says my drive is failing?
If the scan reports uncorrectable errors or finds the same bad sectors repeatedly, your drive is likely failing. Back up your important files immediately and plan to replace the drive. You can usually continue using the computer for a while, but the drive will get worse over time.