Editing Computer data storage (section)

== {{anchor|media}}Storage media ==
{{As of|2011}}, the most commonly used data storage media are semiconductor, magnetic, and optical, while paper still sees some limited usage. Some other fundamental storage technologies, such as all-flash arrays (AFAs) are proposed for development.

=== Semiconductor ===
{{Main|Semiconductor memory}}

[[Semiconductor memory]] uses [[semiconductor]]-based [[integrated circuit]] (IC) chips to store information. Data are typically stored in [[metal–oxide–semiconductor]] (MOS) [[memory cell (computing)|memory cells]]. A semiconductor memory chip may contain millions of memory cells, consisting of tiny [[MOSFET|MOS field-effect transistors]] (MOSFETs) and/or [[MOSFET#MOS capacitor|MOS capacitors]]. Both ''volatile'' and ''non-volatile'' forms of semiconductor memory exist, the former using standard MOSFETs and the latter using [[floating-gate MOSFET]]s.

In modern computers, primary storage almost exclusively consists of dynamic volatile semiconductor [[random-access memory]] (RAM), particularly [[dynamic random-access memory]] (DRAM). Since the turn of the century, a type of non-volatile [[floating-gate]] semiconductor memory known as [[flash memory]] has steadily gained share as off-line storage for home computers. Non-volatile semiconductor memory is also used for secondary storage in various advanced electronic devices and specialized computers that are designed for them.

As early as 2006, [[Laptop|notebook]] and [[desktop computer]] manufacturers started using flash-based [[solid-state drive]]s (SSDs) as default configuration options for the secondary storage either in addition to or instead of the more traditional HDD.<ref>{{Cite web|url=http://www.extremetech.com/article2/0,1558,1966644,00.asp|title=New Samsung notebook replaces hard drive with flash|archive-url=https://web.archive.org/web/20101230081543/http://www.extremetech.com/article2/0,1558,1966644,00.asp|archive-date=30 December 2010|website=Extreme tech|date=23 May 2006|access-date=18 June 2011}}</ref><ref>{{Cite web|url=http://www.technewsworld.com/rsstory/60700.html?wlc=1308338527|title=Toshiba tosses hat into notebook flash storage ring|archive-url=https://web.archive.org/web/20120318100815/http://www.technewsworld.com/rsstory/60700.html?wlc=1308338527|archive-date=18 March 2012|website=technewsworld.com|access-date=18 June 2011}}</ref><ref>{{Cite web|url=https://www.apple.com/macpro/features/storage.html|url-status=dead|title=Mac Pro – Storage and RAID options for your Mac Pro|archive-url=https://web.archive.org/web/20130606070652/http://www.apple.com/macpro/features/storage.html|archive-date=6 June 2013|publisher=Apple|date=27 July 2006|access-date=18 June 2011}}</ref><ref>{{Cite web|url=https://www.apple.com/macbookair/design.html|url-status=dead|title=MacBook Air – The best of iPad meets the best of Mac|archive-url=https://web.archive.org/web/20130527205906/http://www.apple.com/macbookair/design.html|archive-date=27 May 2013|publisher=Apple|access-date=18 June 2011}}</ref><ref>{{Cite web|url=http://news.inventhelp.com/Articles/Computer/Inventions/apple-macbook-air-12512.aspx|url-status=dead|title=MacBook Air replaces the standard notebook hard disk for solid state flash storage|archive-url=https://web.archive.org/web/20110823052120/http://news.inventhelp.com/Articles/Computer/Inventions/apple-macbook-air-12512.aspx|archive-date=23 August 2011|website=news.inventhelp.com|date=15 November 2010|access-date=18 June 2011}}</ref>

=== Magnetic ===
{{Magnetic storage media}}

[[Magnetic storage]] uses different patterns of [[magnetization]] on a [[magnetically]] coated surface to store information. Magnetic storage is ''non-volatile''. The information is accessed using one or more read/write heads which may contain one or more recording transducers. A read/write head only covers a part of the surface so that the head or medium or both must be moved relative to another in order to access data. In modern computers, magnetic storage will take these forms:

* [[Disk storage|Magnetic disk]];
** [[Floppy disk]], used for off-line storage;
** [[Hard disk drive]], used for secondary storage.
* [[Magnetic-tape data storage|Magnetic tape]], used for tertiary and off-line storage;
* [[Carousel memory]] (magnetic rolls).

In early computers, magnetic storage was also used as:

* Primary storage in a form of [[Drum memory|magnetic memory]], or [[core memory]], [[core rope memory]], [[thin-film memory]] and/or [[twistor memory]];
* Tertiary (e.g. [[NCR CRAM]]) or off line storage in the form of magnetic cards;
* Magnetic tape was then often used for secondary storage.

Magnetic storage does not have a definite limit of rewriting cycles like flash storage and re-writeable optical media, as altering magnetic fields causes no physical wear. Rather, their life span is limited by mechanical parts.<ref>{{cite web |title=Comparing SSD and HDD endurance in the age of QLC SSDs|url=https://www.micron.com/-/media/client/global/documents/products/white-paper/5210_ssd_vs_hdd_endurance_white_paper.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.micron.com/-/media/client/global/documents/products/white-paper/5210_ssd_vs_hdd_endurance_white_paper.pdf |archive-date=2022-10-09 |url-status=live|publisher=Micron technology}}</ref><ref>{{cite web|title=Comparing SSD and HDD - A comprehensive comparison of the storage drives|url=https://www.stellarinfo.co.in/kb/ssd-vs-hdd.php |website=www.stellarinfo.co.in|language=en}}</ref>

=== Optical ===
{{Optical storage media}}

[[Optical storage]], the typical [[optical disc]], stores information in deformities on the surface of a circular disc and reads this information by illuminating the surface with a [[laser diode]] and observing the reflection. Optical disc storage is ''non-volatile''. The deformities may be permanent (read only media), formed once (write once media) or reversible (recordable or read/write media). The following forms are in common use {{As of|2009|lc=true}}:<ref>{{Cite web|url=http://www.dvddemystified.com/dvdfaq.html|title=The DVD FAQ - A comprehensive reference of DVD technologies|archive-url=https://web.archive.org/web/20090822172353/http://www.dvddemystified.com/dvdfaq.html|archive-date=22 August 2009}}</ref>

* [[CD]], [[CD-ROM]], [[DVD]], [[BD-ROM]]: Read only storage, used for mass distribution of digital information (music, video, computer programs);
* [[CD-R]], [[DVD-R]], [[DVD+R]], [[BD-R]]: Write once storage, used for tertiary and off-line storage;
* [[CD-RW]], [[DVD-RW]], [[DVD+RW]], [[DVD-RAM]], [[BD-RE]]: Slow write, fast read storage, used for tertiary and off-line storage;
* [[Ultra Density Optical]] or UDO is similar in capacity to [[Blu-ray Disc recordable|BD-R or BD-RE]] and is slow write, fast read storage used for tertiary and off-line storage.

[[Magneto-optical drive|Magneto-optical disc storage]] is optical disc storage where the magnetic state on a [[ferromagnetic]] surface stores information. The information is read optically and written by combining magnetic and optical methods. Magneto-optical disc storage is ''non-volatile'', ''sequential access'', slow write, fast read storage used for tertiary and off-line storage.

[[3D optical data storage]] has also been proposed.

Light induced magnetization melting in magnetic photoconductors has also been proposed for high-speed low-energy consumption magneto-optical storage.<ref name="Náfrádi 2016">{{cite journal|last1=Náfrádi|first1=Bálint|title=Optically switched magnetism in photovoltaic perovskite CH3NH3(Mn:Pb)I3|journal=Nature Communications|date=24 November 2016|volume=7|page=13406|doi=10.1038/ncomms13406|pmc=5123013|pmid=27882917|bibcode=2016NatCo...713406N|arxiv=1611.08205}}</ref>

=== Paper ===
{{Paper data storage media}}

[[Paper data storage]], typically in the form of [[paper tape]] or [[punched card]]s, has long been used to store information for automatic processing, particularly before general-purpose computers existed. Information was recorded by punching holes into the paper or cardboard medium and was read mechanically (or later optically) to determine whether a particular location on the medium was solid or contained a hole. [[Barcode]]s make it possible for objects that are sold or transported to have some computer-readable information securely attached.

Relatively small amounts of digital data (compared to other digital data storage) may be backed up on paper as a [[matrix barcode]] for very long-term storage, as the longevity of paper typically exceeds even magnetic data storage.<ref>{{Cite web|url=https://www.extremetech.com/extreme/134427-a-paper-based-backup-solution-not-as-stupid-as-it-sounds|date=14 August 2012|title=A paper-based backup solution (not as stupid as it sounds)}}</ref><ref>{{Cite magazine|url=https://www.wired.com/2012/08/paperback-paper-backup/|date=16 August 2012|title=PaperBack paper backup|magazine=Wired|last1=Sterling|first1=Bruce}}</ref>

=== Other storage media or substrates ===
; Vacuum-tube memory: A [[Williams tube]] used a [[cathode-ray tube]], and a [[Selectron tube]] used a large [[vacuum tube]] to store information. These primary storage devices were short-lived in the market, since the Williams tube was unreliable, and the Selectron tube was expensive.

; Electro-acoustic memory: [[Delay-line memory]] used [[Longitudinal wave|sound waves]] in a substance such as [[mercury (element)|mercury]] to store information. Delay-line memory was dynamic volatile, cycle sequential read/write storage, and was used for primary storage.

; [[Optical tape]]: is a medium for optical storage, generally consisting of a long and narrow strip of plastic, onto which patterns can be written and from which the patterns can be read back. It shares some technologies with cinema film stock and optical discs, but is compatible with neither. The motivation behind developing this technology was the possibility of far greater storage capacities than either magnetic tape or optical discs.

; [[Phase-change memory]]: uses different mechanical phases of [[phase-change material]] to store information in an X–Y addressable matrix and reads the information by observing the varying [[electrical resistance]] of the material. Phase-change memory would be non-volatile, random-access read/write storage, and might be used for primary, secondary and off-line storage. Most rewritable and many write-once optical disks already use phase-change material to store information.

; [[Holographic data storage]]: stores information optically inside [[crystal]]s or [[photopolymer]]s. Holographic storage can utilize the whole volume of the storage medium, unlike optical disc storage, which is limited to a small number of surface layers. Holographic storage would be non-volatile, sequential-access, and either write-once or read/write storage. It might be used for secondary and off-line storage. See [[Holographic Versatile Disc]] (HVD).

; [[Molecular memory]]: stores information in [[polymer]] that can store electric charge. Molecular memory might be especially suited for primary storage. The theoretical storage capacity of molecular memory is 10&nbsp;terabits per square inch (16&nbsp;Gbit/mm<sup>2</sup>).<ref>{{Cite web|url=https://www.sciencedaily.com/releases/2009/02/090219141438.htm|title=New method of self-assembling nanoscale elements could transform data storage industry|archive-url=https://web.archive.org/web/20090301235710/https://www.sciencedaily.com//releases//2009//02//090219141438.htm|archive-date=1 March 2009|website=sciencedaily.com|date=1 March 2009|access-date=18 June 2011}}</ref>

; Magnetic photoconductors: store magnetic information, which can be modified by low-light illumination.<ref name="Náfrádi 2016"/>

; [[DNA digital data storage|DNA]]: stores information in DNA [[nucleotide]]s. It was first done in 2012, when researchers achieved a ratio of 1.28&nbsp;petabytes per gram of DNA. In March 2017 scientists reported that a new algorithm called a DNA fountain achieved 85% of the theoretical limit, at 215&nbsp;petabytes per gram of DNA.<ref>{{cite news|last1=Yong |first1=Ed|title=This speck of DNA contains a movie, a computer virus, and an Amazon gift card|url=https://www.theatlantic.com/science/archive/2017/03/this-speck-of-dna-contains-a-movie-a-computer-virus-and-an-amazon-gift-card/518373/|access-date=3 March 2017|work=The Atlantic|url-status=live|archive-url=https://web.archive.org/web/20170303010826/https://www.theatlantic.com/science/archive/2017/03/this-speck-of-dna-contains-a-movie-a-computer-virus-and-an-amazon-gift-card/518373/|archive-date=3 March 2017}}</ref><ref>{{cite web|title=Researchers store computer operating system and short movie on DNA|url=https://phys.org/news/2017-03-short-movie-dna.html|website=phys.org |access-date=3 March 2017|url-status=live|archive-url=https://web.archive.org/web/20170302221126/https://phys.org/news/2017-03-short-movie-dna.html|archive-date=2 March 2017}}</ref><ref>{{cite web|title=DNA could store all of the world's data in one room|url=https://www.science.org/content/article/dna-could-store-all-worlds-data-one-room|publisher=Science Magazine|access-date=3 March 2017|date=2 March 2017|url-status=live|archive-url=https://web.archive.org/web/20170302225525/http://www.sciencemag.org/news/2017/03/dna-could-store-all-worlds-data-one-room|archive-date=2 March 2017}}</ref><ref>{{cite journal|last1=Erlich|first1=Yaniv|last2=Zielinski|first2=Dina|title=DNA Fountain enables a robust and efficient storage architecture|journal=Science|date=2 March 2017|volume=355|issue=6328|pages=950–954|doi=10.1126/science.aaj2038|pmid=28254941|url=https://zenodo.org/record/889697|bibcode=2017Sci...355..950E|s2cid=13470340}}</ref>