Bit rot
Bit rot, also known as bit decay, data rot, or data decay, is a colloquial computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...

 term used to describe either a gradual decay of storage media or the degradation of a software program over time. The latter use of the term implies that software can wear out or rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

 like a physical tool. More commonly, bit rot refers to the decay of physical storage media.

Decay of storage media

Bit rot is often defined as the event in which the small electric charge of a bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

 in memory disperses, possibly altering program code.

Bit rot can also be used to describe the phenomenon of data stored in EPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...

s and flash memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

 gradually decaying over the duration of many years, or in the decay of data stored on CD
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

 or DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

 discs or other types of consumer storage.

The cause of bit rot varies depending on the medium. EPROMs and flash memory store data using electrical charges, which can slowly leak away due to imperfect insulation. The chip itself is not affected by this, so re-programming it once per decade or so will prevent the bit rot.

Floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

 and magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...

 storage may experience bit rot as bits lose magnetic orientation, and in warm, humid conditions these media are prone to literal rotting
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...

. In optical discs such as CDs and DVDs the breakdown of the material onto which the data is stored may cause bit rot. This can be mitigated by storing disks in a dark, cool location with low humidity. Archival quality disks are also available. Old punched cards and punched tape
Punched tape
Punched tape or paper tape is an obsolete form of data storage, consisting of a long strip of paper in which holes are punched to store data...

 may also experience literal rotting.

Bit rot is also used to describe the idea that semiconductor RAM may occasionally be altered by cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...

s, a phenomenon known as soft error
Soft error
In electronics and computing, a soft error is an error in a signal or datum which is wrong. Errors may be caused by a defect, usually understood either to be a mistake in design or construction, or a broken component. A soft error is also a signal or datum which is wrong, but is not assumed to...


Problems with software

The term "bit rot" is often used to refer to dormant code rot, i.e. the fact that dormant (unused or little-used) code gradually decays in correctness as a result of interface changes in active code that is called from the dormant code.

A program may run correctly for years with no problem, then malfunction for no apparent reason. Programmers often jokingly attribute the failure to bit rot. Such an effect may be due to a memory leak
Memory leak
A memory leak, in computer science , occurs when a computer program consumes memory but is unable to release it back to the operating system. In object-oriented programming, a memory leak happens when an object is stored in memory but cannot be accessed by the running code...

 or other non-obvious software bug. Often, although there is no obvious change in the program's operating environment, a subtle difference has occurred that is triggering a latent software error. The error in the software may also originate by human operation which allows the construction or derivation of false-positive behavior to occur within the code. Some operating systems tend to lose stability when left running for long periods, which is why they must be restarted occasionally to remove resident errors that have built up due to software errors.

The term is also used to describe the slowing of performance of a PC over time from continued use. One cause of this is installing software or software components that run when the user logs in, causing a noticeable delay in boot
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...

 time. Also, the addition of programs and data on the computer can make operations and searching slower, and sometimes when programs are uninstalled
An uninstaller, also called a deinstaller, is a utility software designed to remove other software or parts of it from a computer. It is the opposite of an installer.-Components:...

 they aren't removed completely. Additionally, fragmentation
Fragmentation (computer)
In computer storage, fragmentation is a phenomenon in which storage space is used inefficiently, reducing storage capacity and in most cases reducing the performance. The term is also used to denote the wasted space itself....

 can slow performance. Normally, unused data (such as a text file containing some notes) does not impede performance of a PC (with the exception of software that, for example, indexes files on a disk to make file searching faster).

See also

  • Link rot
    Link rot
    Link rot , also known as link death or link breaking is an informal term for the process by which, either on individual websites or the Internet in general, increasing numbers of links point to web pages, servers or other resources that have become permanently unavailable...

  • Software rot
    Software rot
    Software rot, also known as code rot or software erosion or software decay or software entropy, is a type of bit rot. It describes the perceived slow deterioration of software over time that will eventually lead to it becoming faulty, unusable, or otherwise in need of maintenance...

  • Digital preservation
    Digital preservation
    Digital preservation is the set of processes, activities and management of digital information over time to ensure its long term accessibility. The goal of digital preservation is to preserve materials resulting from digital reformatting, and particularly information that is born-digital with no...

  • Disc rot
    Disc rot
    Disc rot is a phrase describing the tendency of CD or DVD or other optical disks to become unreadable due to physical or chemical deterioration...

  • Checksum
    A checksum or hash sum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and...

  • Database integrity
    Database integrity
    Database integrity ensures that data entered into the database is accurate, valid, and consistent. Any applicable integrity constraints and data validation rules must be satisfied before permitting a change to the database....

External links

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