page_title: Hard disk drive
section_title: Development
hierarchical_section_title: Hard disk drive / Technology / Development
caption_attribution_description: English: A plot of the leading edge hard disk drive areal densities from 1956 thru 2009 including several trend lines derived from the data.
context_page_description: A hard disk drive, hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital data using 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 even when powered off.
  Introduced by IBM in 1956, HDDs 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 cell phones and tablets, rely on flash products. 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 for servers.
context_section_description: The rate of areal density advancement was similar to Moore's law (doubling every two years) through 2010: 60% per year during 1988–1996, 100% during 1996–2003 and 30% during 2003–2010. Speaking in 1997, Gordon Moore called the increase "flabbergasting", while observing later that growth cannot continue forever. Price improvement decelerated to −12% per year during 2010–2017, as the growth of areal density slowed. The rate of advancement for areal density slowed to 10% per year during 2010–2016, and there was difficulty in migrating from perpendicular recording to newer technologies.
  As bit cell size decreases, more data can be put onto a single drive platter. In 2013, a production desktop 3 TB HDD (with four platters) would have had an areal density of about 500 Gbit/in² which would have amounted to a bit cell comprising about 18 magnetic grains (11 by 1.6 grains). Since the mid-2000s areal density progress has been challenged by a superparamagnetic trilemma involving grain size, grain magnetic strength and ability of the head to write. In order to maintain acceptable signal to noise smaller grains are required; smaller grains may self-reverse (electrothermal instability) unless their magnetic strength is increased, but known write head materials are unable to generate a strong enough magnetic field sufficient to write the medium in the increasingly smaller space taken by grains.
  Magnetic storage technologies are being developed to address this trilemma, and compete with flash memory–based solid-state drives (SSDs). In 2013, Seagate introduced shingled magnetic recording (SMR), intended as something of a "stopgap" technology between PMR and Seagate's intended successor heat-assisted magnetic recording (HAMR), SMR utilises overlapping tracks for increased data density, at the cost of design complexity and lower data access speeds (particularly write speeds and random access 4k speeds). By contrast, Western Digital focused on developing ways to seal helium-filled drives instead of the usual filtered air. This reduces turbulence and friction, and fits more platters into the same enclosure space, though helium gas is notoriously difficult to prevent escaping.
  Other recording technologies are under development as of 2019, including Seagate's heat-assisted magnetic recording (HAMR). HAMR requires a different architecture with redesigned media and read/write heads, new lasers, and new near-field optical transducers. HAMR is expected to ship commercially in late 2020 or 2021. Technical issues delayed the introduction of HAMR by a decade, from earlier projections of 2009, 2015, 2016, and the first half of 2019. Some drives have adopted dual independent actuator arms to increase read/write speeds and compete with SSDs. HAMR's planned successor, bit-patterned recording (BPR), has been removed from the roadmaps of Western Digital and Seagate. Western Digital's microwave-assisted magnetic recording (MAMR), is expected to be shipped commercially in 2021, with sampling in 2020. Two-dimensional magnetic recording (TDMR) and "current perpendicular to plane" giant magnetoresistance (CPP/GMR) heads have appeared in research papers.  A 3D-actuated vacuum drive (3DHD) concept has been proposed.
  The rate of areal density growth has dropped below the historical Moore's law rate of 40% per year. Depending upon assumptions on feasibility and timing of these technologies, Seagate forecasts that areal density will grow 20% per year during 2020–2034.
caption: Leading-edge hard disk drive areal densities from 1956 through 2009 compared to Moore's law. By 2016, progress had slowed significantly below the extrapolated density trend.[75]
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