What checking a hard drive actually does

Checking a hard drive scans the disk for errors, bad sectors, and file system problems that can slow your computer down or cause data loss. The process reads data from different parts of the drive and reports what it finds — it does not fix anything by itself, though most tools can repair common issues automatically if you let them.

On Windows, the built-in tool is called Check Disk (chkdsk). On Mac, it is Disk Utility. Both work similarly: they examine the drive's file system, look for corrupted files, and flag sectors that no longer hold data reliably. Running a check takes anywhere from a few minutes to several hours depending on drive size and how many problems exist.

You should check a drive if your computer freezes randomly, files disappear or become unreadable, you hear clicking sounds from the drive, or you are about to move important files to an external backup.

Key Takeaways

  • Windows Check Disk requires administrator access and works best when run before Windows starts, which means scheduling it to run at the next restart.
  • Mac Disk Utility checks the drive from within macOS and can repair most file system errors without restarting, though some repairs need Safe Mode.
  • Third-party tools like CrystalDiskInfo show you the drive's health status and temperature without making changes, which is useful before deciding whether to replace the drive.
  • A check does not erase your files, but repairing errors can sometimes cause data loss if the drive is already failing, so back up important files first.

How to run Check Disk on Windows

Open File Explorer, right-click the drive you want to check (usually C:), and select Properties. Click the Tools tab, then click Check under Error checking. Windows will ask whether you want to scan the drive now or schedule it for the next restart — choose Schedule the scan.

Restart your computer. Before Windows loads, Check Disk will run automatically and display a progress bar. The scan can take 10 minutes to an hour depending on drive size. Do not turn off the computer while it runs. When finished, Windows will start normally and show a summary of what was found.

If you want more control, you can also open Command Prompt as administrator, type chkdsk C: /F (replace C: with your drive letter), and press Enter. The /F flag tells it to fix errors it finds. Again, Windows will ask you to schedule it for the next restart.

How to check a drive on Mac

Open Applications, go to Utilities, and launch Disk Utility. Select your drive from the list on the left (usually Macintosh HD or similar). Click the First Aid button at the top. Disk Utility will scan the drive and repair file system errors automatically if it finds them.

The scan usually takes a few minutes. If Disk Utility finds problems it cannot repair, it will tell you the drive may need service. Some repairs require restarting into Safe Mode — if that happens, restart your Mac, hold Command-S while it boots, and run First Aid again from Disk Utility.

If you see a message that the drive is locked, it means macOS is currently using it. You can still run the scan, but repairs will be limited. For a full repair, back up your files and restart into Recovery Mode by holding Command-R while the Mac boots, then open Disk Utility from there.

What third-party tools show you that built-in tools do not

Programs like CrystalDiskInfo, Hard Disk Sentinel, and HDTune display the drive's S.M.A.R.T. data — a set of measurements that predict whether a drive is about to fail. They show you the drive's temperature, how many hours it has been powered on, and how many read errors it has recorded. This information helps you decide whether to replace the drive before it fails completely.

These tools are read-only by default, meaning they show you information without making changes. They are useful if you want a second opinion before running a repair, or if you want to monitor a drive's health over time. CrystalDiskInfo is free and works on both Windows and Mac. Hard Disk Sentinel costs money but includes automatic alerts if the drive's health drops.

Third-party tools cannot replace the built-in checkers — they show you the drive's condition but do not repair file system errors the way Check Disk and First Aid do. Use them together: run a third-party tool first to see the drive's overall health, then run the built-in checker if you want to repair errors.

What happens if the check finds bad sectors

A bad sector is a small area of the drive that no longer stores data reliably. When Check Disk or First Aid finds one, it marks that sector as unusable so the operating system will not try to write data there again. This is a normal part of a drive's aging process — a few bad sectors do not mean the drive is about to fail.

If the check finds many bad sectors in a short time, or if it finds them repeatedly after you have already run a repair, the drive is probably failing and should be replaced soon. Back up your files to an external drive or cloud storage before that happens.

Repairing errors can sometimes cause data loss if the drive is already unstable — the repair process writes to the drive, and an unstable drive might lose that data. For this reason, always back up important files before running a full repair, especially if the drive is making unusual sounds or if you have already seen error messages.

When to check a drive versus when to replace it

Check a drive if you have seen a few error messages, the computer has frozen once or twice, or you want to verify the drive is healthy before backing up files. A check is also worth running if you have not done one in over a year and the drive is more than three years old.

Replace the drive if the check finds hundreds of bad sectors, if the drive is making clicking or beeping sounds, if the computer freezes constantly, or if a third-party tool shows the drive's health as Critical or Failed. A drive in that condition can lose data at any moment, so move your files to a new drive or external storage immediately.

If you are unsure, run a third-party health check first — it takes a few minutes and costs nothing. If the tool shows the drive is healthy, a regular check will usually find only minor issues. If it shows the drive is failing, you know to prioritize replacing it.

Frequently Asked Questions

Can I use my computer while a drive check is running?

On Windows, Check Disk runs before the operating system loads, so you cannot use the computer. On Mac, First Aid runs while macOS is running, so you can use the computer, but it will be slower. Avoid opening large files or programs while the scan is in progress.

How often should I check my drive?

Once a year is typical for a healthy drive. If you have seen errors or the drive is more than five years old, check it every few months. If a check finds problems, run it again after a few weeks to see whether new errors have appeared.

Will checking a drive erase my files?

No. A check scans the drive and reports what it finds. Repairs can move or remove corrupted files, but the vast majority of your data stays intact. Back up important files before running repairs if the drive is already showing signs of failure.

What does "volume is in use" mean on Mac?

It means macOS is currently using the drive, so some repairs cannot run. You can still scan the drive, but full repairs require restarting into Recovery Mode. Hold Command-R while the Mac boots, then open Disk Utility and run First Aid again.

Is a clicking sound from the drive serious?

Yes. Clicking usually means the drive's read head is failing and cannot access data reliably. Stop using the drive, back up your files immediately to a different drive, and replace it. Do not run a full check on a clicking drive — the repair process can make the problem worse.