Editing Non-volatile memory

{{short description|Computer memory that does not lose its contents after being turned off}}
{{redirect|Non-volatile||Volatility (disambiguation) {{!}} Volatility}}
{{broader|Computer data storage}}
{{Use dmy dates|date=July 2022}}
{{Memory types}}

'''Non-volatile memory''' ('''NVM''') or '''non-volatile storage''' is a type of [[computer memory]] that can retain stored information even after power is removed. In contrast, [[volatile memory]] needs constant power in order to retain data.

Non-volatile memory typically refers to storage in [[memory chip]]s, which store data in [[floating-gate]] [[memory cell (computing)|memory cells]] consisting of [[floating-gate MOSFET]]s ([[metal–oxide–semiconductor field-effect transistor]]s), including [[Flash memory|flash memory storage]] such as [[NAND flash]] and [[solid-state drive]]s (SSD).

Other examples of non-volatile memory include [[read-only memory]] (ROM), [[EPROM]] (erasable [[programmable ROM]]) and [[EEPROM]] (electrically erasable programmable ROM), [[ferroelectric RAM]], most types of [[computer data storage]] devices (e.g. [[disk storage]], [[hard disk drive]]s, [[optical disc]]s, [[floppy disk]]s, and [[magnetic tape]]), and early computer storage methods such as [[punched tape]] and [[punched card|cards]].<ref>{{cite book |last1=Patterson |first1=David |first2=John |last2=Hennessy |title=Computer Organization and Design: The Hardware/Software Interface |publisher=[[Elsevier]]|date=2005 |page=23 |url=https://books.google.com/books?id=1lD9LZRcIZ8C&pg=PA23|isbn=9780080502571 }}</ref>

==Overview==
Non-volatile memory is typically used for the task of [[secondary storage]] or long-term persistent storage. The most widely used form of [[primary storage]] today{{As of?|date=September 2023}} is a [[Volatile memory|volatile]] form of [[random access memory]] (RAM), meaning that when the [[computer]] is shut down, anything contained in RAM is lost. However, most forms of non-volatile memory have limitations that make them unsuitable for use as primary storage. Typically, non-volatile memory costs more, provides lower performance, or has a limited lifetime compared to volatile random access memory.

Non-volatile data storage can be categorized into electrically addressed systems, for example, [[flash memory]], and [[read-only memory]]) and mechanically addressed systems ([[hard disk]]s, [[optical disc]]s, [[magnetic tape]], [[holographic memory]], and such).<ref>{{cite web|title=i-NVMM: Securing non-volatile memory on the fly|url=http://www.techrepublic.com/blog/it-security/i-nvmm-securing-non-volatile-memory-on-the-fly/|work=[[Techrepublic]]|date=August 2011 |access-date=21 March 2017|url-status=live|archive-url=https://web.archive.org/web/20170322014656/http://www.techrepublic.com/blog/it-security/i-nvmm-securing-non-volatile-memory-on-the-fly/|archive-date=22 March 2017}}</ref><ref>{{cite web|title=Non-Volatile Memory (NVM)|url=https://www.techopedia.com/definition/2793/non-volatile-memory-nvm|publisher=Techopedia|access-date=21 March 2017|url-status=live|archive-url=https://web.archive.org/web/20170322014507/https://www.techopedia.com/definition/2793/non-volatile-memory-nvm|archive-date=22 March 2017}}</ref> Generally speaking, electrically addressed systems are expensive, and have limited capacity, but are fast, whereas mechanically addressed systems cost less per bit, but are slower.

== Electrically addressed ==
{{Main|Non-volatile random-access memory}}

Electrically addressed semiconductor non-volatile memories can be categorized according to their write mechanism. 

=== Read-only and read-mostly devices ===
[[Mask ROM]]s are factory programmable only and typically used for large-volume products which are not required to be updated after the memory device is manufactured. 

[[Programmable read-only memory]] (PROM) can be altered once after the memory device is manufactured using a [[PROM programmer]]. Programming is often done before the device is installed in its target system, typically an [[embedded system]]. The programming is permanent, and further changes require the replacement of the device. Data is stored by physically altering (burning) storage sites in the device.

An [[EPROM]] is an erasable ROM that can be changed more than once. However, writing new data to an EPROM requires a special programmer circuit. EPROMs have a quartz window that allows them to be erased with ultraviolet light, but the whole device is cleared at one time. A [[one-time programmable]] (OTP) device may be implemented using an EPROM chip without the quartz window; this is less costly to manufacture. An electrically erasable programmable read-only memory [[EEPROM]] uses voltage to erase memory. These erasable memory devices require a significant amount of time to erase data and write new data; they are not usually configured to be programmed by the processor of the target system. Data is stored using [[floating-gate transistor]]s, which require special operating voltages to trap or release electric charge on an insulated control gate to store information.

=== Flash memory ===
{{Main|Flash memory}}

[[Flash memory]] is a solid-state chip that maintains stored data without any external power source. It is a close relative to the EEPROM; it differs in that erase operations must be done on a block basis, and its capacity is substantially larger than that of an EEPROM. Flash memory devices use two different technologies—NOR and NAND—to map data. NOR flash provides high-speed random access, reading and writing data in specific memory locations; it can retrieve as little as a single byte. NAND flash reads and writes sequentially at high speed, handling data in blocks. However, it is slower on reading when compared to NOR. NAND flash reads faster than it writes, quickly transferring whole pages of data. Less expensive than NOR flash at high densities, NAND technology offers higher capacity for the same-size silicon.<ref name="Flash1">{{cite magazine |author=Russell Kay |magazine=ComputerWorld |url=http://www.computerworld.com/s/article/349425/Flash_Memory |title=Flash memory |archive-url=https://web.archive.org/web/20100610065251/http://www.computerworld.com/s/article/349425/Flash_Memory |archive-date=10 June 2010 |date=7 June 2010}}</ref>

=== Ferroelectric RAM (F-RAM) ===
{{Main|Ferroelectric RAM}}

'''Ferroelectric RAM''' ('''FeRAM''', '''F-RAM''' or '''FRAM''') is a form of [[random-access memory]] similar in construction to [[DRAM]], both use a capacitor and transistor but instead of using a simple [[dielectric]] layer the capacitor, an F-RAM cell contains a thin ferroelectric film of lead zirconate titanate {{chem2|[Pb(Zr,Ti)O3]}}, commonly referred to as PZT. The Zr/Ti atoms in the PZT change polarity in an electric field, thereby producing a binary switch. Due to the PZT crystal maintaining polarity, F-RAM retains its data memory when power is shut off or interrupted.

Due to this crystal structure and how it is influenced, F-RAM offers distinct properties from other nonvolatile memory options, including extremely high, although not infinite, endurance (exceeding 10<sup>16</sup> read/write cycles for 3.3&nbsp;V devices), ultra-low power consumption (since F-RAM does not require a charge pump like other non-volatile memories), single-cycle write speeds, and gamma radiation tolerance.<ref>{{citation |url=http://www.ramtron.com/about-us/what-is-f-ram.aspx |title=F-RAM Memory Technology |publisher=Ramtron.com |access-date=30 January 2012 |url-status=live |archive-url=https://web.archive.org/web/20120127063617/http://ramtron.com/about-us/what-is-f-ram.aspx |archive-date=27 January 2012}}</ref>

=== Magnetoresistive RAM (MRAM) ===
{{Main|Magnetoresistive random-access memory}}

Magnetoresistive RAM stores data in magnetic storage elements called [[magnetic tunnel junctions]] (MTJs). The first generation of MRAM, such as [[Everspin Technologies]]' 4&nbsp;Mbit, utilized field-induced writing. The second generation is developed mainly through two approaches: [[Thermal-assisted switching]] (TAS)<ref name="white paper">The Emergence of Practical MRAM {{cite web |url=http://www.crocus-technology.com/pdf/BH%20GSA%20Article.pdf |title=Crocus Technology &#124; Magnetic Sensors &#124; TMR Sensors |access-date=2009-07-20 |url-status=dead |archive-url=https://web.archive.org/web/20110427022729/http://www.crocus-technology.com/pdf/BH%20GSA%20Article.pdf |archive-date=27 April 2011}}</ref> which is being developed by [[Crocus Technology]], and [[Spin-transfer torque]] (STT) which [[Crocus Technology|Crocus]], [[Hynix]], [[IBM]], and several other companies are developing.<ref>{{cite web|url=http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=218000269|archive-url=https://web.archive.org/web/20120119111746/http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=218000269|archive-date=19 January 2012|url-status=dead|title=Latest News|website=EE{{!}}Times}}</ref>

=== Phase-change Memory (PCM) ===
{{Main|Phase-change memory}}

Phase-change memory stores data in [[chalcogenide glass]], which can reversibly change the phase between the amorphous and the [[Crystalline|crystalline state]], accomplished by heating and cooling the glass.  The [[crystalline]] state has low resistance, and the amorphous phase has high resistance, which allows currents to be switched ON and OFF to represent digital 1 and 0 states.<ref>{{Cite journal|last1=Hudgens|first1=S.|last2=Johnson|first2=B.|date=November 2004|title=Overview of Phase-Change Chalcogenide Nonvolatile Memory Technology|url=https://www.cambridge.org/core/journals/mrs-bulletin/article/abs/overview-of-phasechange-chalcogenide-nonvolatile-memory-technology/91060FF69176FEC7222376C1E3FA1FC3|journal=MRS Bulletin|language=en|volume=29|issue=11|pages=829–832|doi=10.1557/mrs2004.236|s2cid=137902404 |issn=1938-1425|url-access=subscription}}</ref><ref>{{Cite book|last1=Pirovano|first1=A.|last2=Lacaita|first2=A.L.|last3=Benvenuti|first3=A.|last4=Pellizzer|first4=F.|last5=Hudgens|first5=S.|last6=Bez|first6=R.|title=IEEE International Electron Devices Meeting 2003 |chapter=Scaling analysis of phase-change memory technology |date=December 2003|chapter-url=https://ieeexplore.ieee.org/document/1269376|pages=29.6.1–29.6.4|doi=10.1109/IEDM.2003.1269376|isbn=0-7803-7872-5 |s2cid=1130884 }}</ref>

===FeFET memory===
[[FeFET memory]] uses a transistor with [[ferroelectric]] material to permanently retain state.

===RRAM memory===
{{Main|Resistive random-access memory}}

RRAM (ReRAM) works by changing the resistance across a dielectric solid-state material often referred to as a memristor. ReRAM involves generating defects in a thin oxide layer, known as oxygen vacancies (oxide bond locations where the oxygen has been removed), which can subsequently charge and drift under an electric field. The motion of oxygen ions and vacancies in the oxide would be analogous to the motion of electrons and holes in a semiconductor.

Although ReRAM was initially seen as a replacement technology for flash memory, the cost and performance benefits of ReRAM have not been enough for companies to proceed with the replacement. Apparently, a broad range of materials can be used for ReRAM. However, the discovery <ref>Lee, H. Y.; Chen, P. S.; Wu, T. Y.; Chen, Y. S.; Wang, C. C.; Tzeng, P. J.; Lin, C. H.; Chen, F.; Lien, C. H.; Tsai, M. J. (2008). Low power and high speed bipolar switching with a thin reactive Ti buffer layer in robust Hf{{not a typo}}O2-based RRAM. 2008 IE</ref> that the popular high-κ gate dielectric HfO<sub>2</sub> can be used as a low-voltage ReRAM has encouraged researchers to investigate more possibilities.

== Mechanically addressed systems ==
{{See also|IBM Millipede|holographic memory}}

Mechanically addressed systems use a [[recording head]] to read and write on a designated storage medium. Since the access time depends on the physical location of the data on the device, mechanically addressed systems may be [[sequential access]]. For example, [[magnetic tape]] stores data as a sequence of bits on a long tape; transporting the tape past the recording head is required to access any part of the storage. Tape media can be removed from the drive and stored, giving indefinite capacity at the cost of the time required to retrieve a dismounted tape.<ref>{{cite web|url=http://searchstorage.techtarget.com/definition/tape-drive|title=Definition: tape drive|work=TechTarget|access-date=7 July 2015 |url-status=live |archive-url=https://web.archive.org/web/20150707175544/http://searchstorage.techtarget.com/definition/tape-drive |archive-date=7 July 2015}}</ref><ref>{{cite web |url=http://www.snia.org/education/storage_networking_primer/stor_devices/tape_drives |title=Tape Drives |website=snia.org |access-date=7 July 2015 |url-status=live |archive-url=https://web.archive.org/web/20150707173123/http://www.snia.org/education/storage_networking_primer/stor_devices/tape_drives |archive-date=7 July 2015}}</ref>

[[Hard disk drive]]s use a rotating magnetic disk to store data; access time is longer than for semiconductor memory, but the cost per stored data bit is very low, and they provide random access to any location on the disk. Formerly, removable [[disk pack]]s were common, allowing storage capacity to be expanded.  [[Optical disc]]s store data by altering a pigment layer on a plastic disk and are similarly random access. Read-only and read-write versions are available; removable media again allows indefinite expansion, and some automated systems (e.g. [[optical jukebox]]) were used to retrieve and mount disks under direct program control.<ref>{{cite web|url=http://www.computerhope.com/jargon/h/harddriv.htm|title=What is hard drive?|work=computerhope.com|access-date=7 July 2015|url-status=live|archive-url=https://web.archive.org/web/20150708081114/http://www.computerhope.com/jargon/h/harddriv.htm|archive-date=8 July 2015}}</ref><ref>{{cite web|url=https://www.staff.ncl.ac.uk/roger.broughton/museum/DASD/200426.htm|title=IBM 2314 Disk Drives|work=ncl.ac.uk|access-date=7 July 2015|url-status=dead|archive-url=https://web.archive.org/web/20151002200053/https://www.staff.ncl.ac.uk/roger.broughton/museum/DASD/200426.htm|archive-date=2 October 2015}}</ref><ref>{{cite web|url=http://www.kintronics.com/jukebox.html|title=Optical Blu-ray Jukeboxes and Libraries Systems for Archiving Storage – Kintronics|work=kintronics.com|access-date=7 July 2015|url-status=live|archive-url=https://web.archive.org/web/20150720184226/http://www.kintronics.com/jukebox.html|archive-date=20 July 2015}}</ref>

[[Domain-wall memory|Domain-wall memory (DWM)]] stores data in a [[magnetic tunnel junction]]s (MTJs), which works by controlling [[Domain wall (magnetism)|domain wall (DW)]] motion in ferromagnetic nanowires.<ref>{{Cite journal|last1=Parkin|first1=Stuart S. P.|last2=Hayashi|first2=Masamitsu|last3=Thomas|first3=Luc|date=2008-04-11|title=Magnetic Domain-Wall Racetrack Memory|url=https://www.science.org/doi/abs/10.1126/science.1145799|journal=Science|volume=320 |issue=5873 |pages=190–194 |language=EN|doi=10.1126/science.1145799|pmid=18403702 |bibcode=2008Sci...320..190P |s2cid=19285283 |url-access=subscription}}</ref>

== Organic ==
{{See|Organic electronics}}

[[Thinfilm]] produces rewriteable non-volatile organic [[ferroelectric memory]] based on [[ferroelectric polymer]]s. Thinfilm successfully demonstrated [[roll-to-roll]] [[printed electronics|printed]] memories in 2009.<ref>[http://www.printedelectronicsworld.com/articles/winners_of_the_idtechex_printed_electronics_europe_awards_00001368.asp Thinfilm and InkTec awarded IDTechEx' Technical Development Manufacturing Award] IDTechEx, 15 April 2009</ref><ref>[http://www.eetimes.com/electronics-news/4084606/PolyIC-ThinFilm-announce-pilot-of-volume-printed-plastic-memories PolyIC, ThinFilm announce pilot of volume printed plastic memories] {{webarchive|url=https://web.archive.org/web/20120929080237/http://www.eetimes.com/electronics-news/4084606/PolyIC-ThinFilm-announce-pilot-of-volume-printed-plastic-memories |date=29 September 2012 }} EETimes, 22 September 2009</ref><ref>[http://www.printedelectronicsworld.com/articles/all_set_for_high_volume_production_of_printed_memories_00002179.asp All set for high-volume production of printed memories] {{webarchive|url=https://web.archive.org/web/20100413200959/http://www.printedelectronicsworld.com/articles/all_set_for_high_volume_production_of_printed_memories_00002179.asp |date=13 April 2010 }} Printed Electronics World, 12 April 2010</ref> In Thinfilm's organic memory the ferroelectric polymer is sandwiched between two sets of electrodes in a passive matrix. Each crossing of metal lines is a [[ferroelectric capacitor]] and defines a memory cell.

==Non-volatile main memory==
Non-volatile main memory (NVMM) is [[primary storage]] with non-volatile attributes.<ref>{{cite web|url=https://www.snia.org/sites/default/files/SSSI/NVDIMM%20-%20Changes%20are%20Here%20So%20What's%20Next%20-%20final.pdf|title=NVDIMM – Changes are Here, So What's Next? |publisher=[[Storage Networking Industry Association|SINA]]|website=snia.org|access-date=24 April 2018}}</ref> This application of non-volatile memory presents security challenges.<ref>{{Cite journal|url=https://ieeexplore.ieee.org/document/6952995|title=Security Vulnerabilities of Emerging Nonvolatile Main Memories and Countermeasures|first1=Sachhidh|last1=Kannan|first2=Naghmeh|last2=Karimi|first3=Ozgur|last3=Sinanoglu|first4=Ramesh|last4=Karri|date=22 January 2015|journal=IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems|volume=34|issue=1|pages=2–15|via=IEEE Xplore|doi=10.1109/TCAD.2014.2369741|s2cid=14712674 |url-access=subscription}}</ref> [[NVDIMM]] is one example of the non-volatile main memory.

== References ==
{{Reflist}}

== External links ==
* [https://web.archive.org/web/20181221121125/https://lwn.net/Articles/610174/ Supporting filesystems in persistent memory], [[LWN.net]], 2 September 2014, by Jonathan Corbet
* [http://www.nature.com/articles/ncomms13406 Research paper about perspective usage of magnetic photoconductors in magneto-optical data storage.]

{{Primary storage technologies}}
{{Operating system}}
{{Authority control}}

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[[Category:Non-volatile memory| ]]
[[Category:Computer memory]]