A bad sector in computing is a

disk sector In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs) and 2048 bytes for CD-ROMs and ...

on a

disk storage Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...

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 An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...

will skip it in the future.

Details

A bad sector is the result of mechanical damage, most commonly caused by a

head crash A head crash is a hard-disk failure that occurs when a read–write head of a hard disk drive makes contact with its rotating platter, slashing its surface and permanently damaging its magnetic media. It is most often caused by a sudden seve ...

, manufacturing flaw(s), wear-and-tear, physical shock, sudden power outages, or dust intrusion. Bad sectors are a threat to

information security Information security, sometimes shortened to InfoSec, is the practice of protecting information by mitigating information risks. It is part of Risk management information systems, information risk management. It typically involves preventing or re ...

in the sense of data remanence. Very often physical damages can interfere with parts of many different files.

Operating system

Bad sectors may be detected by the

or the disk controller. Most file systems contain provisions for sectors to be marked as bad, so that the operating system avoids them in the future. Disk diagnostic

utilities A public utility company (usually just utility) is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and ...

, such as

CHKDSK In computing, CHKDSK (short for "check disk") is a system tool and command in DOS, Digital Research FlexOS, IBM/ Toshiba 4690 OS, IBM OS/2, Microsoft Windows and related operating systems. It verifies the file system integrity of a volu ...

(

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...

), Disk Utility (on

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...

), or badblocks (on

) can actively look for bad sectors upon user request.

Disk controller

When a sector is found to be bad or unstable by the firmware of a disk controller, the disk controller remaps the logical sector to a different physical sector. Typically, automatic remapping of sectors only happens when a sector is written to. In the normal operation of a hard drive, the detection and remapping of bad sectors should take place in a manner transparent to the rest of the system and in advance before data is lost. There are two types of remapping by disk hardware: P-LIST (mapping during factory production tests) and G-LIST (mapping during consumer usage by disk microcode). Utilities can read the

Self-Monitoring, Analysis, and Reporting Technology Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T., often written as SMART) is a monitoring system included in computer hard disk drives (HDDs) and solid-state drives (SSDs). Its primary function is to detect and report various indicat ...

(SMART) information to tell how many sectors have been reallocated, and how many spare sectors the drive may still have. Because reads and writes from G-list sectors are automatically redirected (remapped) to spare sectors, it slows down drive access even if data in drive is defragmented. Once the G-list is filled up, the storage unit must be replaced.

Manipulation methods

The

program ATATool can be used to create deliberate bad sectors by manipulating the sector

Error correction code In computing, telecommunication, information theory, and coding theory, an error correction code, sometimes error correcting code, (ECC) is used for controlling errors in data over unreliable or noisy communication channels. The central idea ...

(ECC) data. This can be used to verify bad sector support in disk utilities and forensic tools. For instance, to make sector 10 bad: ATATOOL /BADECC:10 \\.\PhysicalDrive1

References

External links