100 tpi
   HOME

TheInfoList



OR:

Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of
magnetisation In classical electromagnetism, magnetization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material. Movement within this field is described by direction and is either Axial or Dia ...
in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads. Magnetic storage media, primarily
hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...
s, 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 disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
s,
magnetic tape Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magne ...
, and
magnetic stripes The term digital card can refer to a physical item, such as a memory card on a camera, or, increasingly since 2017, to the digital content hosted as a virtual card or cloud card, as a digital virtual representation of a physical card. They share ...
on credit cards.


History

Magnetic storage in the form of wire recording—audio recording on a wire—was publicized by
Oberlin Smith Oberlin Smith (March 22, 1840 – July 19, 1926) was an American engineer who published one of the earliest works dealing with magnetic recording in 1888. Biography He was born on March 22, 1840, in Cincinnati, Ohio, to George R. and Salome (Kemp ...
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 1928,
Fritz Pfleumer Fritz Pfleumer (20 March 1881 – 29 August 1945) was a German engineer who invented magnetic tape for recording sound. Biography Fritz was born as the son of Robert and Minna, née Hünich. His father Robert (1848–1934) was born in Greiz, ...
developed the first magnetic tape recorder. Early magnetic storage devices were designed to record
analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analo ...
audio signals. Computers and now most audio and video magnetic storage devices record
digital data Digital data, in information theory and information systems, is information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits. An example i ...
. In 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

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 A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. When ...
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 A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
. 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 Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally ...
(Fe2O3) 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 each other. 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 Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field. Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk ...
. 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. 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 Air bearings (also known as aerostatic or aerodynamic bearings) are fluid bearings that use a thin film of pressurized gas to provide a low friction load-bearing interface between surfaces. The two surfaces do not touch, thus avoiding the tradit ...
.


Magnetic recording classes


Analog 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 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.


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 disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
s 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 (2020), consumer-grade HDDs offer data storage at about $0.03 per GB. Recording media in 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.


Magneto-optical recording

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 Kerr effect, also called the quadratic electro-optic (QEO) effect, is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index chang ...
. The magnetic medium are typically amorphous R-Fe-Co thin film (R being a rare earth element). Magneto-optical recording is not very popular. One famous example is
Minidisc MiniDisc (MD) is an erasable magneto-optical disc-based data storage format offering a capacity of 60, 74, and later, 80 minutes of digitized audio. Sony announced the MiniDisc in September 1992 and released it in November of that year fo ...
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. 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


Access method

Magnetic storage media can be classified as either sequential access memory or
random access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A Random access, random-access memory device allows data items to b ...
, 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.


Coding schemes

Magnetic disk heads and magnetic tape heads cannot pass DC (direct current), so the coding schemes for both tape and disk data are designed to minimize the DC offset. Most magnetic storage devices use
error correction In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communica ...
. Many magnetic disks internally use some form of run-length limited coding and partial-response maximum-likelihood.


Current usage

, 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 Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magne ...
. 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 disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
s 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

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 Crocus Technology, founded in 2006, is a venture-capital-backed semiconductor startup company developing magnetoresistive random-access memory (MRAM) technology. The company's products originated in a Grenoble-based Spintec laboratory and its te ...
(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 Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both us ...
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. Research is also being done by Aleksei Kimel at Radboud University in the Netherlands towards the possibility of using terahertz radiation rather than using standard electropulses for writing data on magnetic storage media. By using terahertz radiation, writing time can be reduced considerably (50x faster than when using standard electropulses). Another advantage is that terahertz radiation generates almost no heat, thus reducing cooling requirements.Kijk magazine, 12, 2019


See also

* Digital Audio Tape * Digital Data Storage *
Disk storage Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...
* Karlqvist gap * Magnetoresistive random-access memory (MRAM) * Magnetic recording methods: ** Heat-assisted magnetic recording (HAMR) **
Longitudinal magnetic recording Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is acc ...
(LMR) ** Perpendicular magnetic recording (PMR), also known as conventional magnetic recording (CMR) ** Shingled magnetic recording (SMR) * Marvin Camras (1916–1995), American electrical engineer and inventor, major contributor to magnetic recording technology


Reference


External links

*
History of Magnetic Recording
(BBC/H2G2)
''Selected History of Magnetic Recording''

''Oberlin Smith and the Invention of Magnetic Sound Recording''


on the UC San Diego web site (CMRR). *

of Magnetic Recording.

" Science Reporter, VOLUME 43 NUMBER 7 JULY 2006 "Magnetic Recording a Revolutionary Technology" * {{Authority control American inventions Storage media Computer storage media Magnetic devices