It’s not unusual for a hard disk to leave the manufacturing process with a damaged sector; however, this does not affect the overall performance of the disk as the damaged space is considered unusable.

Hard Disk Interfaces and Configuration 
Describes the different major interface standards currently used by hard disks (and other devices). Provides sections about the IDE/ATA and SCSI interfaces. This page is from "The PC Guide."

Fixing Bad Sectors And Lost Allocation Units
Describes how to check for and repair bad sectors or lost allocation units in Microsoft DOS 6.2x.