Below are several digital images illustrating data degradation, all consisting of 326,272 bits. The original photo is displayed on the left. In the next image to the right, a single bit was changed from 0 to 1. In the next two images, two and three bits were flipped. On Linux systems, the binary difference between files can be revealed using cmp command (e.g. cmp -b bitrot-original.jpg bitrot-1bit-changed.jpg).
Data degradation results from the gradual decay of storage media over the course of years or longer. Causes vary by medium:
Solid-state media, such as EPROMs, flash memory and other solid-state drives, store data using electrical charges, which can slowly leak away due to imperfect insulation. The chip itself is not affected by this, so reprogramming it approximately once per decade prevents decay. An undamaged copy of the master data is required for the reprogramming.
Optical media, such as CD-R, DVD-R and BD-R, may experience data decay from the breakdown of the storage medium. This can be mitigated by storing discs in a dark, cool, low humidity location. "Archival quality" discs are available with an extended lifetime, but are still not permanent. However, data integrity scanning that measures the rates of various types of errors is able to predict data decay on optical media well ahead of uncorrectable data loss occurring.
Most disk, disk controller and higher-level systems are subject to a slight chance of unrecoverable failure. With ever-growing disk capacities, file sizes, and increases in the amount of data stored on a disk, the likelihood of the occurrence of data decay and other forms of uncorrected and undetected data corruption increases.
Higher-level software systems may be employed to mitigate the risk of such underlying failures by increasing redundancy and implementing integrity checking, error correction codes and self-repairing algorithms. The ZFS file system was designed to address many of these data corruption issues. The Btrfs file system also includes data protection and recovery mechanisms, as does ReFS.
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^Riss, Dan (July 1993). "Conserve O Gram (number 19/8) Preservation Of Magnetic Media" (PDF). nps.gov. Harpers Ferry, West Virginia: National Park Service / Department of the Interior (US). p. 2. The longevity of magnetic media is most seriously affected by processes that attack the binder resin. Moisture from the air is absorbed by the binder and reacts with the resin. The result is a gummy residue that can deposit on tape heads and cause tape layers to stick together. Reaction with moisture also can result in breaks in the long molecular chains of the binder. This weakens the physical properties of the binder and can result in a lack of adhesion to the backing. These reactions are greatly accelerated by the presence of acids. Typical sources would be the usual pollutant gases in the air, such as sulphur dioxide (SO2) and nitrous oxides (NOx), which react with moist air to form acids. Though acid inhibitors are usually built into the binder layer, over time they can lose their effectiveness.
^"Preserving magnetic media". National Archives of Australia. Retrieved 3 November 2020. High temperature and humidity and fluctuations may cause the magnetic and base layers in a reel of tape to separate, or cause adjacent loops to block together. High temperatures may also weaken the magnetic signal, and ultimately de-magnetise the magnetic layer.
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