Computer data storage or digital data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.
Disk storage is a data storage mechanism based on a rotating disk. The recording employs various electronic, magnetic, optical, or mechanical changes to the disk's surface layer. A disk drive is a device implementing such a storage mechanism. Notable types are hard disk drives (HDD), containing one or more non-removable rigid platters; the floppy disk drive (FDD) and its removable floppy disk; and various optical disc drives (ODD) and associated optical disc media.
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.
A disk read-and-write head is the small part of a disk drive which moves above the disk platter and transforms the platter's magnetic field into electric current or, vice versa, transforms electric current into magnetic field. The heads have gone through a number of changes over the years.
The Digital Compact Cassette (DCC) is a magnetic tape sound recording format introduced by Philips and Matsushita Electric in late 1992 and marketed as the successor to the standard analog Compact Cassette. It was also a direct competitor to Sony's MiniDisc (MD), but neither format toppled the then-ubiquitous analog cassette despite their technical superiority, and DCC was discontinued in October 1996.
Magnetoresistive random-access memory (MRAM) is a type of non-volatile random-access memory which stores data in magnetic domains. Developed in the mid-1980s, proponents have argued that magnetoresistive RAM will eventually surpass competing technologies to become a dominant or even universal memory. Currently, memory technologies in use such as flash RAM and DRAM have practical advantages that have so far kept MRAM in a niche role in the market.
A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc. 130 mm (5.25 in) and 90 mm (3.5 in) discs were the most common sizes. In 1983, just a year after the introduction of the compact disc, Kees Schouhamer Immink and Joseph Braat presented the first experiments with erasable magneto-optical compact discs during the 73rd AES Convention in Eindhoven. The technology was introduced commercially in 1985. Although optical, they normally appear as hard disk drives to an operating system and can be formatted with any file system. Magneto-optical drives were common in some countries, such as Japan, but have fallen into disuse.
In computer data storage, partial-response maximum-likelihood (PRML) is a method for recovering the digital data from the weak analog read-back signal picked up by the head of a magnetic disk drive or tape drive. PRML was introduced to recover data more reliably or at a greater areal-density than earlier simpler schemes such as peak-detection. These advances are important because most of the digital data in the world is stored using magnetic storage on hard disk or tape drives.
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Density is a measure of the quantity of information bits that can be stored on a given length of track, area of the surface, or in a given volume of a computer storage medium. Generally, higher density is more desirable, for it allows more data to be stored in the same physical space. Density therefore has a direct relationship to storage capacity of a given medium. Density also generally affects the performance within a particular medium, as well as price.
Heat-assisted magnetic recording (HAMR) is a magnetic storage technology for greatly increasing the amount of data that can be stored on a magnetic device such as a hard disk drive by temporarily heating the disk material during writing, which makes it much more receptive to magnetic effects and allows writing to much smaller regions.
Disk packs and disk cartridges were early forms of removable media for computer data storage, introduced in the 1960s.
In 1953, IBM recognized the immediate application for what it termed a "Random Access File" having high capacity and rapid random access at a relatively low cost. After considering technologies such as wire matrices, rod arrays, drums, drum arrays, etc., the engineers at IBM's San Jose California laboratory invented the hard disk drive. The disk drive created a new level in the computer data hierarchy, then termed Random Access Storage but today known as secondary storage, less expensive and slower than main memory but faster and more expensive than tape drives.
Higher performance in hard disk drives comes from devices which have better performance characteristics. These performance characteristics can be grouped into two categories: access time and data transfer time .
Shingled magnetic recording (SMR) is a magnetic storage data recording technology used in hard disk drives (HDDs) to increase storage density and overall per-drive storage capacity. Conventional hard disk drives record data by writing non-overlapping magnetic tracks parallel to each other, while shingled recording writes new tracks that overlap part of the previously written magnetic track, leaving the previous track narrower and allowing higher track density. Thus, the tracks partially overlap similar to roof shingles. This approach was selected because, if the writing head is made too narrow, it cannot provide the very high fields required in the recording layer of the disk.
Solid-state storage (SSS) is non-volatile computer storage that has no moving parts – uses only electronic circuits. This solid-state design dramatically differs from the commonly-used competing technology of electromechanical magnetic storage which uses moving media coated with magnetic material. Generally, SSS is much faster but more expensive for the same amount of storage.
Bruce Alvin Gurney was an American physicist responsible for pioneering advances in magnetic recording. In particular, he was central to the development of the giant magnetoresistance (GMR) sensors first used in hard disk drives in 1997.
Christopher Henry Bajorek is a data storage engineer noted for his leadership in developing and implementing magnetoresistive sensors into magnetic stripe readers, tape drives and hard disk drives.
Robert E Fontana is an engineer, physicist, and author who is noted for his contributions in the areas of magnetic recording and data storage on hard disk drives (HDD) and on digital tape recorders. His work has concentrated on developing thin film processing techniques for nano-fabrication of magnetic devices including Giant Magnetoresistance read heads now used universally in magnetic recording. Much of his career was with IBM in San Jose, California. He is a Fellow of the Institute of Electrical and Electronics Engineers and a member of the National Academy of Engineering.
David A. Thompson is an American electrical engineer and inventor with a long career at IBM. He is noted for his many contributions to magnetic recording technology. Thompson was inducted into the National Inventors Hall of Fame for the invention and development of the thin-film inductive head and the magnetoresistive read head. These heads are now ubiquitous in all hard-disk drives and magnetic tape recorders.
