What a disk check does and when you need one
A disk check scans your hard drive for errors in how data is stored and organized, then fixes what it finds. You run one when your computer is slow, freezes often, won't start up, or shows error messages about corrupted files. The scan takes 15 minutes to several hours depending on your drive size and how many errors exist.
On Windows, the tool is called Check Disk (or chkdsk). On Mac, it's Disk Utility. Both work the same way: they look for bad sectors (physical damage on the drive), lost file fragments, and broken links in the file system. If they find problems, they repair them automatically or flag them for you to fix.
You don't need to run a disk check every week. Run one when your computer shows signs of trouble, or once or twice a year as maintenance if you use your computer heavily.
Key Takeaways
- Windows Check Disk can run in the background while you work, or restart your computer to run a full scan that fixes more problems.
- Mac Disk Utility must be run from Recovery Mode, which you enter by restarting and holding Command+R during startup.
- A full disk check on Windows takes 10 to 60 minutes depending on drive size; Mac scans usually take 5 to 15 minutes.
- If the scan finds errors it cannot fix, your drive may be failing and you should back up your files when ready.
How to run Check Disk on Windows 10 and 11
The fastest way is to let Windows run a quick scan without restarting. Open File Explorer, right-click on your C: drive (or whichever drive you want to check), select Properties, then click the Tools tab. Under Error checking, click Check. Windows will ask if you want to scan and fix errors — click Scan and repair drive. The scan runs in the background while you use your computer, and you'll see results when it finishes.
If you want a deeper scan that fixes more problems, you need to restart your computer. Open Settings, go to System, then About. Click Advanced system settings, then the Tools tab, then Check now under Error checking. Check both boxes: Automatically fix file system errors and Scan for and attempt recovery of bad sectors. Click Start. Windows will ask to schedule the scan for the next restart — click Yes. Restart your computer. The scan will run before Windows loads, which takes 10 to 60 minutes depending on your drive size. Do not turn off your computer during this scan.
How to run Disk Utility on Mac
Disk Utility on Mac must run from Recovery Mode, which means your regular operating system is not running. Restart your Mac and hold Command+R as it starts up. Keep holding until you see the Apple logo or a spinning globe. Release the keys. Your Mac will load into Recovery Mode, which looks different from your normal desktop.
Once in Recovery Mode, click Utilities in the menu bar, then Disk Utility. In the left sidebar, click your main drive (usually named Macintosh HD). Click the First Aid button at the top. Disk Utility will scan your drive and repair errors automatically. This usually takes 5 to 15 minutes. When it finishes, click Done, then close Disk Utility. Go to the Apple menu and select Restart to return to your normal Mac.
If First Aid finds errors it cannot repair, your drive may be failing. Back up your files when ready using Time Machine or by copying them to an external drive.
What to do if the scan finds errors
If Check Disk or Disk Utility reports that it fixed errors, your computer should run better. You don't need to do anything else — the repairs are already done. Restart your computer normally and see if the slowness or freezing has stopped.
If the scan reports errors it could not fix, or if it finds the same errors again on a second scan, your hard drive is likely failing. This is not something a disk check can solve. Back up all your important files to an external drive or cloud storage (Google Drive, OneDrive, iCloud) right away. Then contact a computer repair shop or your computer's manufacturer about replacing the drive. A failing drive can stop working suddenly, so do not wait.
If the scan finds no errors but your computer is still slow, the problem is not disk corruption. Look at what programs are running at startup, how much free space you have left on the drive, or whether your RAM is full — those are separate issues with separate solutions.
Why a disk check is different from other cleanup tools
Disk check only fixes structural problems with how your drive stores data. It does not delete old files, clear your browser cache, remove duplicate photos, or uninstall programs you don't use. Those are what other tools like Disk Cleanup (Windows) or Storage Management (Mac) do.
If your computer is slow because your drive is almost full, a disk check will not help. You need to delete files or move them to external storage. If your computer is slow because too many programs run at startup, a disk check will not help either. You need to disable startup programs in Settings (Windows) or System Preferences (Mac).
Run a disk check when you suspect file corruption or drive damage. Run cleanup tools when you need to free up space. They solve different problems.
How often to run a disk check
For most people, once or twice a year is enough. Run one in spring and fall as routine maintenance, or run one whenever your computer shows signs of trouble: repeated freezing, error messages about corrupted files, slow startup, or files that won't open.
If you use your computer for heavy work — video editing, large file transfers, running many programs at once — you can run a disk check every three months. If you mostly browse the web and check email, once a year is fine.
Do not run a disk check every day or every week. It puts stress on your drive and is unnecessary. The only exception is if you are troubleshooting a specific problem — in that case, run it once, see if it fixes the issue, and then go back to your normal schedule.
Frequently Asked Questions
Can I use my computer while a disk check is running?
On Windows, a quick scan runs in the background and you can use your computer normally. A full scan (the one that requires a restart) runs before Windows loads, so you cannot use your computer during it. On Mac, you must restart into Recovery Mode, so you cannot use your computer at all during the scan.
What if my computer won't start up?
On Windows, restart your computer and press F8 repeatedly as it starts. Select Repair Your Computer, then Troubleshoot, then Advanced Options, then Command Prompt. Type chkdsk C: /F and press Enter. On Mac, restart and hold Command+S to enter Single-User Mode, then type fsck -fy and press Enter. Both will run a disk check before your normal operating system loads.
Does a disk check delete my files?
No. A disk check only repairs the structure of your file system. It does not delete, move, or change your files. If it finds broken file fragments, it may mark them as unusable, but your intact files stay where they are.
How do I know if my drive is actually failing?
Signs include: the same errors appearing after multiple disk checks, clicking or beeping sounds from inside your computer, files that suddenly become unreadable, or the scan taking much longer than usual. If you see any of these, back up your files when ready and contact a repair shop.
Is there a difference between Check Disk and CHKDSK?
No. CHKDSK is the command-line version of Check Disk. Both do the same thing. Use the graphical Check Disk tool in Settings if you prefer clicking buttons, or open Command Prompt and type chkdsk if you prefer typing commands. The results are identical.