text:
Magnetic storage
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2012) (Learn how and when to remove this template message)
Longitudinal recording and perpendicular recording, two types of writing heads on a hard disk.
Magnetic storage or magnetic recording is the storage of data on a magnetised medium. Magnetic storage uses different patterns of magnetisation in a magnetisable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.
As of 2017[update], magnetic storage media, primarily hard disks, are widely used to store computer data as well as audio and video signals. In the field of computing, the term magnetic storage is preferred and in the field of audio and video production, the term magnetic recording is more commonly used. The distinction is less technical and more a matter of preference. Other examples of magnetic storage media include floppy disks, magnetic recording tape, and magnetic stripes on credit cards.
Contents
[hide]
1 History
2 Design
3 Magnetic recording classes
3.1 Analog recording
3.2 Digital recording
3.3 Magneto-optical recording
3.4 Domain propagation memory
4 Technical details
4.1 Access method
5 Current usage
6 Future
7 See also
8 References
9 External links
History[edit]
Magnetic storage in the form of wire recording—audio recording on a wire—was publicized by Oberlin Smith in the Sept 8, 1888 issue of the Electrical World. Smith had previously filed a patent in September, 1878 but found no opportunity to pursue the idea as his business was machine tools. The first publicly demonstrated (Paris Exposition of 1900) magnetic recorder was invented by Valdemar Poulsen in 1898. Poulsen's device recorded a signal on a wire wrapped around a drum. In 1928, Fritz Pfleumer developed the first magnetic tape recorder. Early magnetic storage devices were designed to record analog audio signals. Computers and now most audio and video magnetic storage devices record digital data.
In old computers, magnetic storage was also used for primary storage in a form of magnetic drum, or core memory, core rope memory, thin film memory, twistor memory or bubble memory. Unlike modern computers, magnetic tape was also often used for secondary storage.
Design[edit]
Hard drives use magnetic memory to store giga- and terabytes of data in computers.
Information is written to and read from the storage medium as it moves past devices called read-and-write heads that operate very close (often tens of nanometers) over the magnetic surface. The read-and-write head is used to detect and modify the magnetisation of the material immediately under it. There are two magnetic polarities, each of which is used to represent either 0 or 1.
The magnetic surface is conceptually divided into many small sub-micrometer-sized magnetic regions, referred to as magnetic domains, (although these are not magnetic domains in a rigorous physical sense), each of which has a mostly uniform magnetisation. Due to the polycrystalline nature of the magnetic material each of these magnetic regions is composed of a few hundred magnetic grains. Magnetic grains are typically 10 nm in size and each form a single true magnetic domain. Each magnetic region in total forms a magnetic dipole which generates a magnetic field. In older hard disk drive (HDD) designs the regions were oriented horizontally and parallel to the disk surface, but beginning about 2005, the orientation was changed to perpendicular to allow for closer magnetic domain spacing.
For reliable storage of data, the recording material needs to resist self-demagnetisation, which occurs when the magnetic domains repel each other. Magnetic domains written too densely together to a weakly magnetisable material will degrade over time due to rotation of the magnetic moment one or more domains to cancel out these forces. The domains rotate sideways to a halfway position that weakens the readability of the domain and relieves the magnetic stresses. Older hard disk drives used iron(III) oxide as the magnetic material, but current disks use a cobalt-based alloy.[1]
A write head magnetises a region by generating a strong local magnetic field, and a read head detects the magnetisation of the regions. Early HDDs used an electromagnet both to magnetise the region and to then read its magnetic field by using electromagnetic induction. Later versions of inductive heads included Metal In Gap (MIG) heads and thin film heads. As data density increased, read heads using magnetoresistance (MR) came into use; the electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of spintronics; in read heads, the magnetoresistive effect was much greater than in earlier types, and was dubbed "giant" magnetoresistance (GMR). In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive.[2]
The heads are kept from contacting the platter surface by the air that is extremely close to the platter; that air moves at or near the platter speed. The record and playback head are mounted on a block called a slider, and the surface next to the platter is shaped to keep it just barely out of contact. This forms a type of air bearing.
Magnetic recording classes[edit]
Analog recording[edit]
Main article: Magnetic tape sound recording
Analog recording is based on the fact that remnant magnetisation of a given material depends on the magnitude of the applied field. The magnetic material is normally in the form of tape, with the tape in its blank form being initially demagnetised. When recording, the tape runs at a constant speed. The writing head magnetises the tape with current proportional to the signal. A magnetisation distribution is achieved along the magnetic tape. Finally, the distribution of the magnetisation can be read out, reproducing the original signal. The magnetic tape is typically made by embedding magnetic particles (approximately 0.5 micrometers [3] in size) in a plastic binder on polyester film tape. The most commonly-used of these was ferric oxide, though chromium dioxide, cobalt, and later pure metal particles were also used. Analog recording was the most popular method of audio and video recording. Since the late 1990s, however, tape recording has declined in popularity due to digital recording[4].
Digital recording[edit]
Instead of creating a magnetisation distribution in analog recording, digital recording only needs two stable magnetic states, which are the +Ms and -Ms on the hysteresis loop. Examples of digital recording are floppy disks and hard disk drives (HDDs). Digital recording has also been carried out on tapes. However, HDDs offer superior capacities at reasonable prices; at the time of writing (2014), consumer-grade HDDs offer data storage at about 3 GB/$.
Recording media on HDDs use a stack of thin films to store information and a read/write head to read and write information to and from the media; various developments have been carried out in the area of used materials.[5]
Magneto-optical recording[edit]
Magneto-optical recording writes/reads optically. When writing, the magnetic medium is heated locally by a laser, which induces a rapid decrease of coercive field. Then, a small magnetic field can be used to switch the magnetisation. The reading process is based on magneto-optical Kerr effect. The magnetic medium are typically amorphous R-FeCo thin film (R being a rare earth element). Magneto-optical recording is not very popular. One famous example is Minidisc developed by Sony.
Domain propagation memory[edit]
Domain propagation memory is also called bubble memory. The basic idea is to control domain wall motion in a magnetic medium that is free of microstructure. Bubble refers to a stable cylindrical domain. Data is then recorded by the presence/absence of a bubble domain. Domain propagation memory has high insensitivity to shock and vibration, so its application is usually in space and aeronautics.
Technical details[edit]
Access method[edit]
Magnetic storage media can be classified as either sequential access memory or random access memory, although in some cases the distinction is not perfectly clear. The access time can be defined as the average time needed to gain access to stored records. In the case of magnetic wire, the read/write head only covers a very small part of the recording surface at any given time. Accessing different parts of the wire involves winding the wire forward or backward until the point of interest is found. The time to access this point depends on how far away it is from the starting point. The case of ferrite-core memory is the opposite. Every core location is immediately accessible at any given time.
Hard disks and modern linear serpentine tape drives do not precisely fit into either category. Both have many parallel tracks across the width of the media and the read/write heads take time to switch between tracks and to scan within tracks. Different spots on the storage media take different amounts of time to access. For a hard disk this time is typically less than 10 ms, but tapes might take as much as 100 s.
Current usage[edit]
As of 2011[update], common uses of magnetic storage media are for computer data mass storage on hard disks and the recording of analog audio and video works on analog tape. Since much of audio and video production is moving to digital systems, the usage of hard disks is expected to increase at the expense of analog tape. Digital tape and tape libraries are popular for the high capacity data storage of archives and backups. Floppy disks see some marginal usage, particularly in dealing with older computer systems and software. Magnetic storage is also widely used in some specific applications, such as bank cheques (MICR) and credit/debit cards (mag stripes).
Future[edit]
A new type of magnetic storage, called magnetoresistive random-access memory or MRAM, is being produced that stores data in magnetic bits based on the tunnel magnetoresistance (TMR) effect. Its advantage is non-volatility, low power usage, and good shock robustness. The 1st generation that was developed was produced by Everspin Technologies, and utilized field induced writing.[6] The 2nd generation is being developed through two approaches: thermal-assisted switching (TAS)[7] which is currently being developed by Crocus Technology, and spin-transfer torque (STT) on which Crocus, Hynix, IBM, and several other companies are working.[8] However, with storage density and capacity orders of magnitude smaller than an HDD, MRAM is useful in applications where moderate amounts of storage with a need for very frequent updates are required, which flash memory cannot support due to its limited write endurance.[citation needed] Six state MRAM is also being developed, echoing four bit multi level flash memory cells, that have six different bits, as opposed to two.[9]
See also[edit]
Digital Audio Tape
Digital Data Storage
Disk storage
Heat-assisted magnetic recording
Karlqvist gap
Magnetoresistive Random Access Memory
Marvin Camras
Shingled magnetic recording
References[edit]
Jump up ^ Kanellos, Michael (24 August 2006). "A divide over the future of hard drives". CNETNews.com. Retrieved 24 June 2010.
Jump up ^ "IBM OEM MR Head | Technology | The era of giant magnetoresistive heads". Hitachigst.com. 27 August 2001. Archived from the original on 2015-01-05. Retrieved 4 September 2010.
Jump up ^ "Magnetic Tape Recording". Hyperphysics.phy-astr.gsu.edu. Retrieved 2014-01-28.
Jump up ^ E. du Trémolete de Lacheisserie, D. Gignoux, and M. Schlenker (editors), Magnetism: Fundamentals, Springer, 2005
Jump up ^ Developments in Data Storage, ed. S.N. Piramanayagam and Tow C. Chong, IEEE-Wiley Press (2012).
Jump up ^ MRAM Technology Attributes Archived June 10, 2009, at the Wayback Machine.
Jump up ^ The Emergence of Practical MRAM http://www.crocus-technology.com/pdf/BH%20GSA%20Article.pdf
Jump up ^ "Tower invests in Crocus, tips MRAM foundry deal". EE Times. Archived from the original on 2012-01-19. Retrieved 2014-01-28.
Jump up ^ "Researchers design six-state magnetic memory". phys.org. Retrieved 2016-05-23.
External links[edit]
A History of Magnetic Recording (BBC/H2G2)
Selected History of Magnetic Recording
Oberlin Smith and the Invention of Magnetic Sound Recording
History of Magnetic Recording on the UC San Diego web site (CMRR).
A Chronology of Magnetic Recording.
[1] " Science Reporter, ISSN 0036-8512 VOLUME 43 NUMBER 7 JULY 2006 "Magnetic Recording a Revolutionary Technology"
"Know Your Digital Storage Media: a guide to the most common types of digital storage media found in archives". USA: University of Texas at San Antonio.
[hide]
v
t
e
Magnetic storage media
Wire (1898)
Tape (1928)
Drum (1932)
Ferrite core (1949)
Hard disk (1956)
Stripe card (1956)
MICR (1956)
Thin film (1962)
CRAM (1962)
Twistor (~1968)
Floppy disk (1969)
Bubble (~1970)
MRAM (1995)
Racetrack (2008)
Authority control
NDL: 00574731
Retrieved from "https://en.wikipedia.org/w/index.php?title=Magnetic_storage&oldid=804824513"
Categories:
American inventions
Storage media
Computer storage media
Magnetic devices
Hidden categories:
Webarchive template wayback links
Articles needing additional references from October 2012
All articles needing additional references
Articles containing potentially dated statements from 2017
All articles containing potentially dated statements
Articles containing potentially dated statements from 2011
All articles with unsourced statements
Articles with unsourced statements from March 2008
Navigation menu
Personal tools
Not logged in
Talk
Contributions
Create account
Log in
Namespaces
Article
Talk
Variants
Views
Read
Edit
View history
More
Search
Navigation
Main page
Contents
Featured content
Current events
Random article
Donate to Wikipedia
Wikipedia store
Interaction
Help
About Wikipedia
Community portal
Recent changes
Contact page
Tools
What links here
Related changes
Upload file
Special pages
Permanent link
Page information
Wikidata item
Cite this page
Print/export
Create a book
Download as PDF
Printable version
Languages
العربية
Български
한국어
Հայերեն
Bahasa Indonesia
Italiano
עברית
日本語
Norsk
Polski
Română
Simple English
Türkçe
Українська
中文
Edit links
This page was last edited on 11 October 2017, at 11:25.
Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
Privacy policy
About Wikipedia
Disclaimers
Contact Wikipedia
Developers
Cookie statement
Mobile view

values: mw-page-base noprint

values: mw-head-base noprint

attrs: id class style

values: firstHeading firstHeading en

values: siteSub noprint

values: jump-to-nav mw-jump

values: Help:Introduction to referencing with Wiki Markup/1

values: plainlinks metadata ambox ambox-content ambox-Refimprove

values:
plainlinks noprint asof-tag update
display:none;

values:
/wiki/Recording_tape
mw-redirect
Recording tape

values:
/wiki/Signal_(electrical_engineering)
mw-redirect
Signal (electrical engineering)

values:
/wiki/Primary_storage
mw-redirect
Primary storage

values:
/wiki/Magnetic_drum
mw-redirect
Magnetic drum

values:
/wiki/Core_memory
mw-redirect
Core memory

values:
/wiki/Thin_film_memory
mw-redirect
Thin film memory

values:
/wiki/Magnetic_domains
mw-redirect
Magnetic domains

values: Edit section: Magnetic recording classes

values:
/wiki/Magnetic_tape_sound_recording
mw-redirect
Magnetic tape sound recording

values:
/wiki/Random_access_memory
mw-redirect
Random access memory

values: This claim needs references to reliable sources. (March 2008)

values:
noprint Inline-Template Template-Fact
white-space:nowrap;

values:
nofollow
external text
http://www.everspin.com/technology.html

values: -moz-column-width: 30em; -webkit-column-width: 30em; column-width: 30em; list-style-type: decimal;

values:
nofollow
external text
http://www.bbc.co.uk/dna/h2g2/A3224936

values: International Standard Serial Number (identifier)

values:
nofollow
http://lib.utsa.edu/knowyourmedia/
external text

values: nowraplinks collapsible autocollapse navbox-inner

values: Category:Webarchive template wayback links

values: Category:Articles needing additional references from October 2012

values: Category:All articles needing additional references

values: Category:Articles containing potentially dated statements from 2017

values: Category:All articles containing potentially dated statements

values: Category:Articles containing potentially dated statements from 2011

values: Category:All articles with unsourced statements

values: Category:Articles with unsourced statements from March 2008

values: Discussion about edits from this IP address [ctrl-alt-n]

values: A list of edits made from this IP address [ctrl-alt-y]

values: You are encouraged to create an account and log in; however, it is not mandatory

values: You're encouraged to log in; however, it's not mandatory. [ctrl-alt-o]

values:
/wiki/Magnetic_storage
View the content page [ctrl-alt-c]
c

values: Discussion about the content page [ctrl-alt-t]

values: p-namespaces navigation vectorTabs p-namespaces-label

values:
p-variants
navigation
vectorMenu emptyPortlet
p-variants-label

values: Past revisions of this page [ctrl-alt-h]

values: p-views navigation vectorTabs p-views-label

values:
p-cactions
navigation
vectorMenu emptyPortlet
p-cactions-label

values:
mw-wiki-logo
/wiki/Main_Page
Visit the main page

values:
/wiki/Main_Page
Visit the main page [ctrl-alt-z]
z

values: Featured content – the best of Wikipedia

values: Find background information on current events

values:
/wiki/Special:Random
Load a random article [ctrl-alt-x]
x

values: portal navigation p-navigation p-navigation-label

values: Guidance on how to use and edit Wikipedia

values: About the project, what you can do, where to find things

values: A list of recent changes in the wiki [ctrl-alt-r]

values: portal navigation p-interaction p-interaction-label

values: List of all English Wikipedia pages containing links to this page [ctrl-alt-j]

values: Recent changes in pages linked from this page [ctrl-alt-k]

values:
/wiki/Wikipedia:File_Upload_Wizard
Upload files [ctrl-alt-u]
u

values: A list of all special pages [ctrl-alt-q]

values: Permanent link to this revision of the page

values: Link to connected data repository item [ctrl-alt-g]

values: Printable version of this page [ctrl-alt-p]

values:
uls-settings-trigger
Language settings
0
button
true

values: تخزين مغناطيسي – Arabic

values: Магнитен запис – Bulgarian

values: 자기 디스크 – Korean

values: Մագնիսական նյութեր – Armenian

values: מדיה מגנטית – Hebrew

values: Dispozitiv de stocare magnetic – Romanian

values: Магнітний запис – Ukrainian

values: mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject page-Magnetic_storage rootpage-Magnetic_storage vector-nav-directionality skin-vector action-view