What Check Disk does and when to use it

Check Disk is a Windows tool that scans your hard drive or solid-state drive for errors and can repair some of them automatically. It checks the file system — the structure that organizes your files — and looks for bad sectors, which are small areas of the drive that no longer store data reliably. On older mechanical drives, bad sectors happen naturally over time. On newer drives, they are rarer but still possible.

You should run Check Disk if your computer is slow to start up, files take a long time to open, you see error messages about corrupted files, or Windows crashes unexpectedly. You might also run it after a power failure, a forced shutdown, or if your drive makes clicking or grinding sounds. Check Disk cannot fix every problem — if the drive itself is failing, no software repair will stop that — but it can catch and repair file system damage before it spreads.

On a Mac, the equivalent tool is called Disk Utility, which works differently and is covered separately. This article covers Windows only.

Key Takeaways

  • Check Disk scans for file system errors and bad sectors; you run it from the command prompt or by right-clicking the drive in File Explorer.
  • The tool works best when you schedule it to run at the next system restart, because Windows cannot scan the active drive while you are using it.
  • A full scan with repair can take hours on a large drive, so plan to run it when you do not need the computer.
  • Check Disk cannot fix hardware failure; if the drive is physically failing, the scan may slow down or freeze, and you should back up your data immediately.

Running Check Disk from File Explorer

The simplest way to start a Check Disk scan is through File Explorer. Open File Explorer, right-click the drive you want to scan (usually C: for your main drive), and select Properties. Click the Tools tab, then click Check under the "Error checking" section. Windows will ask whether you want to scan the drive now or schedule it for the next restart.

If the drive is currently in use — which it will be if you are scanning your main Windows drive — Windows cannot scan it while you are logged in. You will see a message saying "The type of the file system is NTFS. You cannot run this utility now because the volume is in use by another process." Click Schedule the disk check. The scan will run the next time you restart your computer, before Windows fully loads. Do not interrupt the restart; let the scan finish, which can take 10 minutes to several hours depending on drive size and the number of errors found.

Running Check Disk from the Command Prompt

For more control, you can run Check Disk from the command prompt. Press the Windows key, type cmd, right-click Command Prompt, and select Run as administrator. Type the command chkdsk C: /F /R and press Enter. The /F flag tells Check Disk to fix errors; the /R flag tells it to locate bad sectors and recover readable information. Replace C: with the letter of the drive you want to scan if it is different.

If you are scanning your main drive, Windows will ask whether you want to schedule the check for the next restart. Type Y and press Enter. The scan will run at the next startup. If you are scanning a secondary drive that is not in use, the scan can run immediately without restarting.

You can also use chkdsk C: without the /F or /R flags to run a read-only scan that reports errors but does not fix them. This is useful if you want to see what problems exist before committing to a repair.

Understanding the scan results

When Check Disk finishes, it displays a summary showing the total disk space, the number of files and directories, and whether any errors were found and fixed. If it found bad sectors, it will report how many and whether it recovered the data. If the scan found no errors, the drive is healthy as far as the file system is concerned.

If Check Disk reports a large number of bad sectors or cannot repair errors, the drive may be failing. In that case, back up your important files to an external drive or cloud storage as soon as possible. A drive with many bad sectors will eventually become unusable, and the more errors accumulate, the slower the repair process becomes.

How long Check Disk takes

A quick scan of a small drive can finish in 5 to 10 minutes. A full scan with repair on a large drive — especially a mechanical hard drive — can take 2 to 8 hours or longer. Solid-state drives scan faster than mechanical drives because they have no moving parts and can read data more quickly.

The time also depends on how many errors Check Disk finds. If it discovers bad sectors, it spends time trying to recover data from them, which slows the process. Do not interrupt the scan by restarting or shutting down; let it finish completely. If you force a shutdown during a scan, you risk corrupting the file system further.

When Check Disk cannot help

Check Disk repairs file system errors — the organizational structure of your drive — but it cannot fix hardware failure. If your drive is physically failing, no software tool can reverse that. Signs of hardware failure include the drive making clicking, beeping, or grinding sounds; the computer freezing or becoming extremely slow; or files disappearing or becoming inaccessible without explanation.

If you suspect hardware failure, back up your data immediately and consider having the drive replaced. Running Check Disk on a failing drive may speed up the failure because the scan puts stress on the drive. If the scan freezes or takes far longer than expected, stop it and back up your data instead of waiting for it to finish.

Frequently Asked Questions

Can I use my computer while Check Disk is running?

No. If you scheduled Check Disk to run at startup, it runs before Windows fully loads, and you cannot use the computer until it finishes. If you try to use the computer during the scan, Windows will pause the scan, which defeats the purpose. Plan to let the computer sit undisturbed until the scan completes.

What does the /R flag do that /F does not?

The /F flag fixes errors in the file system structure. The /R flag goes further: it locates bad sectors on the drive and tries to recover any readable data from them, then marks those sectors as unusable so Windows will not try to write to them again. Use /R if you suspect bad sectors; use /F alone if you only want to fix file system corruption.

Will Check Disk delete my files?

Check Disk may move corrupted files to a folder called Found.000 on the drive root if it cannot repair them. The files inside are usually unrecoverable, but Check Disk does not intentionally delete anything. If you are worried about data loss, back up your drive before running a repair scan.

Should I run Check Disk regularly?

You do not need to run it on a schedule. Run it only when you notice signs of trouble — slow performance, error messages, or unexpected crashes. Running it too often on a healthy drive wastes time. If you find yourself running Check Disk every few weeks and it keeps finding errors, the drive is likely failing and should be replaced.