Internal hard-drive defect management is a system present in

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magneti ...

s for handling of

bad sector A bad sector in computing is a disk sector on a disk storage unit that is permanently damaged. Upon taking damage, all information stored on that sector is lost. When a bad sector is found and marked, the operating system like Windows or Linux will ...

s. The systems are generally proprietary and vary from manufacturer to manufacturer, but typically consist of a "P" (for "permanent" or "primary") list of bad sectors detected in the manufacturing stage and a "G" (for "growth") list of bad sectors that crop up after manufacturing. Many disk/controller subsystems reserve storage to remap defective disk sectors. The drive automatically creates its initial remapping information and has the additional ability to dynamically remap "grown" defects. Because the drive is remapping its own bad sectors, software may not detect growing numbers of bad sectors until later stages of gradual hard-disk failure (which in some cases may not be until after the warranty period has expired.)

References

Hard disk drives {{tech-stub