What is a Sector?

A sector is a small area on the surface of a hard drive or a floppy disk.

Hard drives usually have several platters. The platters are the discs which are covered with magnetic material which is used to hold data. Floppy disk drives contain only one platter.

Platters are divided into a set of concentric rings called tracks. A 1.44MB floppy disk has 160 tracks. Hard drives have thousands of tracks.

Each of these tracks is divided into smaller storage areas called sectors. A sector is the smallest storage area on a disk.

What is a Bad Sector?

Hard drives are contain millions of sectors. It is very normal for some of these sectors to be bad sectors, even when the drive is first manufactured.

In addition, a small number of sectors will normally go bad during the lifespan of a drive.

When this happens, the data in those sectors may be lost, but the data on the rest of the disk will be unaffected and the disk is still completely usable.

A bad sector cannot be repaired, but it can be marked as unusable. Once marked as unusable, the Operating System will know not to attempt to store data in that bad sector. The storage capacity of the disk will be decreased by the amount of storage space in the bad sector.

If your hard drive develops a bad sector, back the hard drive up immediately. If the bad sector was caused by a faulty drive head, the problem can quickly spread to other sectors on the disk.

To learn how to repair a bad sector, read How do I repair a bad sector?