|This article's factual accuracy is disputed. (January 2014)|
The Jargon File, a compendium of hacker's lore, defines "bit rot" as a jocular explanation for the software rot, the degradation of a software program over time even if "nothing has changed"; an explanations is that bits are subject to decay as if they were radioactive.
Decay of storage media
Bit rot is often defined as the event in which the small electric charge of a bit in memory disperses, possibly altering program code or stored data. The hypothesis that semiconductor RAM may occasionally be altered by cosmic rays is also known as soft error.
Bit rot can also be used to describe the phenomenon of storage media gradually decaying over the duration of many years. The cause of bit rot varies depending on the medium:
- Solid state media – such as EPROMs, flash memory and other solid-state drives – stores 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 bit rot. The biggest problem can be finding a clean copy of the chip from which to make the copy; frequently, by the time the user discovers the bit rot, there are no un-damaged chips to use as a master.
- Magnetic media – such as floppy disks and magnetic tapes – may experience bit rot as bits lose their magnetic orientation. Periodic refreshing by rewriting the data can alleviate this problem. Also, in warm and humid conditions these media are prone to literal rotting.
- Optical media – such as CD-R, DVD-R and BD-R – may experience bit rot from the breakdown of the material onto which the data is stored. This can be mitigated by storing discs in a dark, cool location with low humidity. "Archival quality" discs are also available, but do not necessarily provide a permanent solution to the onset of bit rot or other types of data corruption beyond a certain amount of time. Some media (such as M-DISC) are designed to improve longevity over DVD-R and BD-R.
- Paper media – such as punched cards and punched tape – may also experience literal rotting. Mylar punched tape is available for use in this situation.
Component and system failures
Most disk, disk controller and higher level systems are subject to a small degree 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 bit rot 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 and self-repairing algorithms. The ZFS file system was designed to address many of these issues. The Btrfs file system also includes data protection and recovery mechanisms, and so does ReFS.
- Raymond, Eric. "Bit rot". The Jargon File. Retrieved 3 March 2013.
- O'Gorman, T. J.; Ross, J. M.; Taber, A. H.; Ziegler, J. F.; Muhlfeld, H. P.; Montrose, C. J.; Curtis, H. W.; Walsh, J. L. (January 1996). "Field testing for cosmic ray soft errors in semiconductor memories". IBM Journal of Research and Development 40 (1): 41–50. doi:10.1147/rd.401.0041. Retrieved 4 March 2013.
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