Magnetic Storage

Summary

Magnetic storage is a durable and nonvolatile way of recording analog, digital, and alphanumerical data. In most applications, an electric current is used to generate a variable magnetic field over a specially prepared tape or disk that imprints the tape or disk with patterns that, when “read” by an electromagnetic drive “head,” duplicates the wavelengths of the original signal. Magnetic storage has been a particularly enduring technology, as the original conceptual designs were published in the late nineteenth century.

Definition and Basic Principles

Magnetic storage describes one method in which recorded information is stored for later access. A magnetized medium can be one or a combination of several different substances: iron wire, steel bands, strips of paper or cotton string coated with powdered iron filings, cellulose or polyester tape coated with iron oxide or chromium oxide particles, or aluminum or ceramic disks coated with multiple layers of nonmetallic alloys overlaid with a thin layer of a magnetic (typically a ferrite) alloy. The varying magnetic structures are encoded with alphanumerical data and become a temporary or permanent nonvolatile repository of that data. Typical uses of magnetic storage media range from magnetic recording tape and hard and floppy computer disks to the striping material on the backs of credit, debit, and identification cards as well as certain kinds of bank checks.

Background and History

American engineer Oberlin Smith’s 1878 trip to Thomas Alva Edison’s laboratory in Menlo Park, New Jersey, was the source for Smith’s earliest prototypes of a form of magnetic storage. Disappointed by the poor recording quality of Edison’s wax cylinder phonograph, Smith imagined a different method for recording and replaying sound. In the early 1820s, electrical pioneers such as Hans Ørsted demonstrated basic electromagnetic principleslectrical current, when run through an iron wire, could generate a magnetic field, and electrically charged wires affected each other magnetically. Smith toyed with the idea but did not file a patent—possibly because he never found the time to construct a complete, working model. On September 8, 1888, he finally published a description of his conceptual design, involving a cotton cord woven with iron filings passing through a coil of electrically charged wire, in Electrical World magazine. The concept in the article, “Some Possible Forms of Phonograph,” though theoretically possible, was never tested.

The first actual magnetic audio recording was Danish inventor Valdemar Poulsen’s telegraphone, developed in 1896 and demonstrated at the Exposition Universelle in Paris in 1900. The telegraphone was composed of a cylinder, cut with grooves along its surface, wrapped in steel wire. The electromagnetic head, as it passed over the tightly wrapped iron wire, operated both in recording sound and in playing back the recorded audio. Poulsen, trying to reduce distortion in his recordings, had also made early attempts at biasing (increasing the fidelity of a recording by including a DC current in his phonograph model) but, like Oberlin Smith’s earlier model, his recorders, based on wire, steel tape, and steel disks, could not easily be heard and lacked a method of amplification.

Austrian inventor Fritz Pfleumer was the originator of magnetic tape recording. Since Pfleumer was accustomed to working with paper (his business was cigarette paper manufacturing), he created the original magnetic tape by gluing pulverized iron particles (ferrous oxide) onto strips of paper that could be wound into rolls. Pfleumer also constructed a tape recorder to use his tape. On January 31, 1928, Pfleumer received German patent DE 500900 for his sound record carrier (lautschriftträger), unaware that an American inventor, Joseph O’Neill, had filed a patent—the first—for a device that magnetically recorded sound in December 1927.

How It Works

The theory underlying magnetic storage and magnetic recording is simple. An electrical or magnetic current imprints patterns on the magnetic storage medium. Magnetic tape, magnetic hard and floppy disks, and other forms of magnetic media operate similarly—an electric current is generated and applied to a demagnetized surface to vary the substratum and form a pattern based on variations in the electrical current. The biggest differences between the three dominant types of magnetic storage media (tape, rigid or hard disks, and flexible or floppy disks) are the varying speeds at which stored data can be recovered.

Magnetic Tape. Magnetic tape was used extensively for archival computer data storage and analog sound or video recording. The ferrous- or chromium-impregnated plastic tape, initially demagnetized, passes at a constant rate over a recording head, generating a weak magnetic field proportional to the audio or video impulses being recorded and selectively magnetizing the tape's surface. Although durable, given the correct storage conditions, magnetic tape has the significant disadvantage of being consecutively ordered—the recovery of stored information depends on how quickly the spooling mechanism within the recorder can operate. Sometimes, the demand for high-density, cheap data storage outweighs the slower data access rate. Large computer systems commonly archived information on magnetic tape cassettes or cartridges. Despite the archaic form, advances in tape density allowed magnetic tape cassettes to store up to five terabytes (TB) of data in uncompressed formats.

For audio or video applications, sequential retrieval of information (watching a movie or listening to a piece of music) is the most common method, so a delay in locating a particular part is regarded with greater tolerance. Analog tape was an industry standard for recording music, film, and television until the advent of optical storage, which uses a laser to encode data streams into a recordable media disk and is less affected by temperature and humidity.

Magnetic Disks. Two other types of recordable magnetic media are the hard and floppy diskettes—both of which involve the imprinting of data onto a circular disk or platter. The ease and speed of access to recorded information encouraged the development of a new magnetic storage media form for the computer industry. The initial push to develop a nonlinear system resulted, in 1956, with the unveiling of IBM’s 350 Disk Storage Unit—an early example of what became known as a hard drive. Circular, ferrous-impregnated aluminum disks were designed to spin at a high rate of speed and were written upon or read by magnetic heads moving radially over the disk’s surface.

Hard and floppy disks differ only in the range of components available within a standard unit. Hard disks, composed of a spindle of disks and a magnetic read-write apparatus, are typically located inside a metal case. Floppy disks, on the other hand, were packaged as a single or dual-density magnetic disk (separate from the read-write apparatus that encodes them) inside a plastic cover. Floppy disks, because they do not contain recording hardware, were intended to be more portable (and less fragile) than hard disks—a trait that made them extremely popular for home computer users.

Another variant of the disk-based magnetic storage technology is magneto-optical recording. Like an optical drive, magneto-optical recording operates by burning encoded information with a laser and accessing the stored information through optical means. Unlike an optical storage medium, a magneto-optical drive directs its laser at the layer of magnetic material. In 1992, Sony released the MiniDisc, an unsuccessful magneto-optical storage medium.

Applications and Products

Applications for magnetic storage range from industrial or institutional uses to private-sector applications, but the technology underlying each of these formats is functionally the same. The technology that created so many different inventions based on electrical current and magnetic imprinting also had a big impact on children’s toys. The Magna Doodle, a toy developed in 1974, demonstrates a simple application of the concept behind magnetic storage that can shed light on how the more complex applications of the technology also work. In this toy, a dense, opaque fluid encapsulates fine iron filings between two thin sheets of plastic. The upper layer of plastic is transparent and thin enough that the weak magnetic current generated by a small magnet encased in a cylinder of plastic (a magnetic pen) can make the iron filings float to the surface of the opaque fluid and form a visible dark line. Any images produced by the pen are, like analog audio signals encoded into magnetic tape, nonvolatile and remain visible until manually erased by a strip of magnets passing over the plastic and drawing the filings back under the opaque fluid.

Magnetic Tape Drives. It is this basic principle of nonvolatile storage that underlies the usage of the three basic types of magnetic storage media—magnetic tape, hard disks, and floppy disks. All three have been used for a wide variety of purposes. Magnetic tape, whether in the form of steel bands, paper, or any one of a number of plastic formulations, was the original magnetic media and was extensively used by the technologically developed nations to capture audio and, eventually, video signals. It long remained the medium of choice for archival mainframe data storage because large computer systems intended for mass data archival require a system of data storage that was both capable of recording vast amounts of information in a minimum of space (high-density) and was extremely inexpensive—two qualities inherent to magnetic tape. Internet-based (or "cloud") storage began to replace physical archival tapes in the 2010s.

Early versions of home computers also had magnetic tape drives as a secondary method of data storage. In the 1970s, IBM offered its version of a magnetic cassette tape recorder (compatible with its desktop computer) that used the widely available cassette tape. By 1985, however, hard disks and floppy disks had dominated the market for computer systems designed to access smaller amounts of data frequently and quickly, and cassette tapes became obsolete for home computer data storage.

Hard Disk Drives. In 1955, IBM’s 350 Disk Storage Unit, one of the computer industry’s earliest hard drives, had only a five-megabyte (MB) capacity despite its massive size. It contained a spindle of fifty twenty-four-inch disks in a casing the size of a large refrigerator. The 350 was the first of a long series of hard drives with ever-increasing storage capacity. Between 1950 and 2010, the average area density of a hard drive doubled every few years, starting from about three megabytes to the high-end availability of three terabytes by 2010. Higher-capacity drives remained in development as computer companies, such as Microsoft, Seagate, and Western Digital, redefined the basic unit of storage capacity on a hard drive from 512 bytes (IBM’s standard unit established in the 1980s) to 4 to 10 terabytes of the late 2010s. By the 2020s, hard disk drives reached more than 30 terabytes while remaining relatively small.

Early hard drives, such as IBM’s 350, were huge (88 cubic feet) and prohibitively expensive (around USD$15,000 per megabyte of data capacity). Since commercial sales of IBM computers to nongovernmental customers increased rapidly, IBM wanted to find a way to deliver software updates to clients cheaply and efficiently. Consequently, engineers separated a hard disk’s components into two units—the recording mechanism (the drive) and the recording medium (the floppy disk). The size of the typical hard drive made it difficult to transport and caused the 1971 development of another similar form of magnetic media—the floppy disk.

Floppy Disk Drives. The floppy disk itself, even in its initial eight-inch diameter, was a fraction of the weight and size needed for a contemporary hard disk. Because of the rapidly increasing storage needs of the most popular computer programs, smaller disk size and higher disk density became the goal of the major producers of magnetic media—Memorex, Shugart, and Mitsumi, among others. As with the hard drive, floppy disk size and storage capacity, respectively, decreased and increased over time until the 3.5-inch floppy disk became the industry standard. Similarly, the physical dimensions of hard drives also shrank from 88 cubic feet to 2.5 cubic inches, allowing portable external hard drives to enter the market. Floppy disks were made functionally obsolete when another small, cheap, portable recording device came on the market—the thumb or flash drive. Sony, the last major manufacturer of floppy disks, ceased floppy disk production in March 2011.

Magnetic Striping. Magnetic storage, apart from tape and disks, is also widely used for the frequent transmission of small amounts of exclusively personal data—namely, the strip of magnetic tape located on the back of credit, debit, and identification cards as well as the ferrous-impregnated inks that are used to print numbers along the bottom of paper checks. Since durability over time is a key factor, encasing the magnetic stripe into a durable plastic card became the industry standard for banks and other lending institutions. In 2015, credit and debit cards began featuring embedded microchips and traditional magnetic stripes to enhance data security. By the 2020s, most major banks and credit card companies had implemented chips, though the magnetic strip had remained on the cards as a backup feature.

Careers and Course Work

Individuals interested in further developing the technology of magnetic media should study computer engineering, electrical engineering, or materials engineering depending on whether they wish to pursue increasing the storage capacity of the existing electromagnetic technology or finding alternative methods of using electromagnetic theory on data storage problems. Some universities are particularly sensitive to the related nature of computer component design and electrical system design and allow for a dual degree in both disciplines. Supplemental coursework in information technology would also be helpful, as an understanding of how networks transmit data will more precisely define where future storage needs may be anticipated and remedied.

Social Context and Future Prospects

The ongoing social trend, both locally and globally, is to seek to collect and store vast amounts of data that, nevertheless, must be readily accessible. An example of this is in meteorology, which has been attempting for decades to formulate complex computer models to predict weather trends based on previous trends observed and recorded globally over a century. Weather and temperature records are increasingly detailed, so computer storage for the ideal weather-predicting computer will need to keep up with the storage requirements of a weather system archive and meet reasonable deadlines for accessing and evaluating a century’s atmospheric data.

Though less commonly used than cloud storage in modern technology, several magnetic-tape data storage devices continue to be produced, such as IBM’s 3592, released in 2023, and the linear tape-open Ultrium technology (LTO-9), released in 2021. These technologies are often used as a backup.

Other storage developments will probably center on making more biometric data immediately available in identification card striping. Another archival-related goal might be the increasing need for quick comparisons of DNA evidence in various law enforcement sectors.

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