HDD Bad Sectors Explained: What They Are and How to Fix Them

What Are Bad Sectors?

The HDD surface is divided into small sectors — typically 512 bytes or 4096 bytes each. A bad sector is a sector where data cannot be reliably written or read. There are two types:

Physical (Hard) bad sectors: caused by physical damage — head-to-surface contact (head crash), impact, dust particles or magnetic wear. These sectors cannot be 'fixed' — they are permanently damaged.

Logical (Soft) bad sectors: caused by a write error or unexpected drive disconnection. In many cases these can be resolved through rewriting or remapping.

Symptoms of Bad Sectors

How to tell if your drive has bad sectors:

• Computer runs unusually slowly when reading files • Files open with an error or are corrupted • Windows/macOS takes long to boot or freezes • CHKDSK or Disk Utility reports errors • Computer restarts or freezes without warning • Clicking sounds from the HDD location

If you notice several of these symptoms, immediately run a SMART check (free with CrystalDiskInfo on Windows) or seek professional diagnostics.

Bad Sector Repair and Remapping

Remapping procedure: HDDs have reserve sectors — a special area to which the drive firmware moves data from damaged sectors. This process is called remapping. After remapping, the damaged sector is marked unusable and data is stored in the reserve sector.

Is remapping a long-term solution? A small number of remapped sectors is normal for any HDD. However, a growing count is a warning sign. If new bad sectors appear each week, the drive is approaching full failure. In this case, immediately back up all data and plan drive replacement.

Impact on data: data in a physical bad sector zone is permanently lost. For logical bad sectors, data can often be recovered before remapping.

What to Do When Bad Sectors Are Found

1. Immediately back up all important data — copy to another drive, cloud storage or USB.

2. Run CHKDSK /r (Windows) or fsck (Linux) — these tools attempt to remap logical bad sectors and repair the file system.

3. Contact specialists if CHKDSK doesn't resolve the issue or the bad sector count is growing — professional diagnostics and surface restoration with PC-3000 hardware.

4. Plan drive replacement — an HDD with a growing bad sector count is unreliable and will likely fail completely within months.