The hard disk is the storage device of a computer. It consists mostly of a magnetic disk and a mechanical arm that writes information to the disk. The magnetic disk is divided into smaller pieces called groups or sectors. Damaged sectors can cause information on the hard drive to corrupt or even further damage the hard drive. Modern hard drives come with extra sectors that will start to be used automatically when the originals are damaged. There are several factors that can cause damage to the sector of a hard drive.