Magnetic storage in the context of "External hard drive"

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 magnetic tape can with relative ease record and play back audio, visual, and binary computer data.

Magnetic tape revolutionized sound recording and reproduction and broadcasting. It allowed radio, which had always been broadcast live, to be recorded for later or repeated airing. Since the early 1950s, magnetic tape has been used with computers to store large quantities of data and is still used for backup purposes.

A floppy disk, diskette, or floppy diskette (casually known as a floppy or a disk) is a type of disk storage made from a thin, flexible disk coated with a magnetic storage medium. It is enclosed in a square or nearly square plastic shell lined with fabric to help remove dust from the spinning disk. Floppy disks store digital data, which can be read or written when inserted into a floppy disk drive (FDD) connected to or built into a computer or other device. The three most popular formats of floppy disks (and their drives) are the 8-inch, 5¼-inch, and 3½-inch versions.

The first floppy disks, invented and made by IBM in 1971, had a disk diameter of 8 inches (203.2 mm). Subsequently, the 5¼-inch (130 mm) and then the 3½-inch (90 mm) became a ubiquitous form of data storage and transfer into the first years of the 21st century. By the end of the 1980s, 5¼-inch disks had been superseded by 3½-inch disks. During this time, PCs frequently came equipped with drives of both sizes. By the mid-1990s, 5¼-inch drives had virtually disappeared, as the 3½-inch disk became the predominant floppy disk. The advantages of the 3½-inch disk were its higher capacity, its smaller physical size, and its rigid case which provided better protection from dirt and other environmental risks.

Disc and disk are both variants of the English word for objects of a generally thin and cylindrical geometry. The differences in spelling correspond both with regional differences and with different senses of the word. For example, in the case of flat, rotational data storage media the convention is that the spelling disk is used for magnetic storage (e.g., hard disks) while disc is used for optical storage (e.g., compact discs, better known as CDs). When there is no clear convention, the spelling disk is more popular in American English, while the spelling disc is more popular in British English.

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 magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small rectangular box, possibly in a disk enclosure for portability.

Hard disk drives were introduced by IBM in 1956, and were the dominant secondary storage device for general-purpose computers beginning in the early 1960s. HDDs maintained this position into the modern era of servers and personal computers, though personal computing devices produced in large volume, like mobile phones and tablets, rely on flash memory storage devices. More than 224 companies have produced HDDs historically, though after extensive industry consolidation, most units are manufactured by Seagate, Toshiba, and Western Digital. HDDs dominate the volume of storage produced (exabytes per year) for servers. Though production is growing slowly (by exabytes shipped), sales revenues and unit shipments are declining, because solid-state drives (SSDs) have higher data-transfer rates, higher areal storage density, somewhat better reliability, and much lower latency and access times.

Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. Colloquially, when a magnet is "magnetized", it has remanence. The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and is used as a source of information on the past Earth's magnetic field in paleomagnetism. The word remanence is derived from remanent, meaning "that which remains".

The equivalent term residual magnetization is generally used in engineering applications. In transformers, electric motors and generators a large residual magnetization is not desirable (see also electrical steel) as it is an unwanted contamination, for example, a magnetization remaining in an electromagnet after the current in the coil is turned off. Where it is unwanted, it can be removed by degaussing.

Magnetostatics is the study of magnetic fields in systems where the currents are steady (not changing with time). It is the magnetic analogue of electrostatics, where the charges are stationary. The magnetization need not be static; the equations of magnetostatics can be used to predict fast magnetic switching events that occur on time scales of nanoseconds or less. Magnetostatics is even a good approximation when the currents are not static – as long as the currents do not alternate rapidly. Magnetostatics is widely used in applications of micromagnetics such as models of magnetic storage devices as in computer memory.