Magnetic storage or magnetic recording is the storage of data on a
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
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
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
7 See also
9 External links
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
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
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
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.
Hard drives use magnetic memory to store giga- and terabytes of data
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.
Older hard disk drives used iron(III) oxide as the magnetic material,
but current disks use a cobalt-based alloy.
For reliable storage of data, the recording material needs to resist
self-demagnetisation, which occurs when the magnetic domains repel
Magnetic domains written too close together in a weakly
magnetisable material will degrade over time due to rotation of the
magnetic moment of 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.
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
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
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  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
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.
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
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
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.
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.
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
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.
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).
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. The 2nd generation is being
developed through two approaches: thermal-assisted switching (TAS)
which is currently being developed by Crocus Technology, and
spin-transfer torque (STT) on which Crocus, Hynix, IBM, and several
other companies are working. 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. Six state MRAM is
also being developed, echoing four bit multi level flash memory cells,
that have six different bits, as opposed to two.
Digital Audio Tape
Heat-assisted magnetic recording
Magnetoresistive Random Access Memory
Shingled magnetic recording
^ Ley, Willy (August 1965). "The Galactic Giants". For Your
Information. Galaxy Science Fiction. pp. 130–142.
^ Kanellos, Michael (24 August 2006). "A divide over the future of
hard drives". CNETNews.com. Retrieved 24 June 2010.
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.
^ "Magnetic Tape Recording". Hyperphysics.phy-astr.gsu.edu. Retrieved
^ E. du Trémolete de Lacheisserie, D. Gignoux, and M. Schlenker
(editors), Magnetism: Fundamentals, Springer, 2005
^ Developments in
Data Storage, ed. S.N. Piramanayagam and Tow C.
Chong, IEEE-Wiley Press (2012).
^ MRAM Technology Attributes Archived June 10, 2009, at the Wayback
^ The Emergence of Practical MRAM "Archived copy" (PDF). Archived from
the original (PDF) on 2011-04-27. Retrieved 2009-07-20.
^ "Tower invests in Crocus, tips MRAM foundry deal". EE Times.
Archived from the original on 2012-01-19. Retrieved 2014-01-28.
^ "Researchers design six-state magnetic memory". phys.org. Retrieved
A History of Magnetic Recording (BBC/H2G2)
Selected History of Magnetic Recording
Oberlin Smith and the Invention of Magnetic
History of Magnetic Recording on the UC San Diego web site (CMRR).
A Chronology of Magnetic Recording.
 " 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
Magnetic storage media
Ferrite core (1949)
Hard disk (1956)
Stripe card (1956)
Thin film (1962)
Floppy disk (1969)