Editing Hard disk drive (section)

== Technology ==
[[File:magneticMedia.svg|thumb|Magnetic cross section & [[frequency modulation]] encoded binary data]]

=== Magnetic recording ===
{{See also|Magnetic storage}}

A modern HDD records data by magnetizing a thin film of [[ferromagnetic material]]{{Efn|Initially gamma iron oxide particles in an epoxy binder, the recording layer in a modern HDD typically is domains of a granular Cobalt-Chrome-Platinum-based alloy physically isolated by an oxide to enable [[perpendicular recording]].<ref>{{Cite arXiv |title=New Paradigms in Magnetic Recording |eprint = 1201.5543|last1 = Plumer|first1 = M. L.|last2 = van Ek|first2 = J.|last3 = Cain|first3 = W. C.|year = 2012|class = physics.pop-ph}}</ref>}} on both sides of a disk. Sequential changes in the direction of magnetization represent binary data [[bit]]s. The data is read from the disk by detecting the transitions in magnetization.  User data is encoded using an encoding scheme, such as [[run-length limited]] encoding,{{Efn|Historically a variety of run-length limited codes have been used in magnetic recording including for example, codes named [[Frequency modulation|FM]], [[Modified Frequency Modulation|MFM]] and [[Group Coded Recording|GCR]] which are no longer used in modern HDDs.}} which determines how the data is represented by the magnetic transitions.

A typical HDD design consists of a ''{{visible anchor|spindle|Spindle}}'' that holds flat circular disks, called [[hard disk drive platter|platters]], which hold the recorded data. The platters are made from a non-magnetic material, usually [[aluminum alloy]], [[glass]], or [[ceramic]]. They are coated with a shallow layer of magnetic material typically 10–20 [[nanometer|nm]] in depth, with an outer layer of carbon for protection.<ref name="headcrash" /><ref name="AutoMK-6" /><ref name="AutoMK-7"  /> For reference, a standard piece of copy paper is {{convert|0.07|-|0.18|mm|nm|sp=us|abbr=on}}<ref name="AutoMK-8" /> thick.

[[File:Toshiba MK1403MAV - broken glass platter-93375.jpg|thumb|left|Destroyed hard disk, glass platter visible]]
[[File:Hard drive-en.svg|thumb|left|Diagram labeling the major components of a computer HDD]]
[[File:Aufnahme einzelner Magnetisierungen gespeicherter Bits auf einem Festplatten-Platter..jpg|thumb|Recording of single magnetisations of bits on a 200&nbsp;MB HDD-platter (recording made visible using CMOS-MagView)<ref name="AutoMK-9" />]]
[[File:Perpendicular Recording Diagram.svg|thumb|Longitudinal recording (standard) & [[perpendicular recording]] diagram]]

The platters in contemporary HDDs are spun at speeds varying from {{val|4200|ul=rpm}} in energy-efficient portable devices, to 15,000&nbsp;rpm for high-performance servers.<ref name="AutoMK-10" /> The first HDDs spun at 1,200&nbsp;rpm<ref name="IBM350" /> and, for many years, 3,600&nbsp;rpm was the norm.<ref>{{cite web |url=https://www.karlstechnology.com/blog/hard-drive-spindle-speed/ |title=Hard Drive Spindle Speed |publisher=The PC Guide |last=Kozierok |first=Charles |access-date=May 26, 2019 |date=October 20, 2018 |archive-url=https://web.archive.org/web/20190526103244/https://www.karlstechnology.com/blog/hard-drive-spindle-speed/ |archive-date=May 26, 2019 |url-status=live }}</ref> {{As of|November 2019}}, the platters in most consumer-grade HDDs spin at 5,400 or 7,200&nbsp;rpm.

Information is written to and read from a platter as it rotates past devices called [[disk read-and-write head|read-and-write heads]] that are positioned to operate very close to the magnetic surface, with their [[flying height]] often in the range of tens of nanometers. The read-and-write head is used to detect and modify the magnetization of the material passing immediately under it.

In modern drives, there is one head for each magnetic platter surface on the spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc (roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the platter as it spins. The arm is moved using a [[voice coil]] actuator or, in some older designs, a [[stepper motor]]. Early hard disk drives wrote data at some constant bits per second, resulting in all tracks having the same amount of data per track, but modern drives (since the 1990s) use [[zone bit recording]], increasing the write speed from inner to outer zone and thereby storing more data per track in the outer zones.

In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of [[superparamagnetism|thermal effects]]⁠ ⁠— thermally induced magnetic instability which is commonly known as the "[[superparamagnetic limit]]". To counter this, the platters are coated with two parallel magnetic layers, separated by a three-atom layer of the non-magnetic element [[ruthenium]], and the two layers are magnetized in opposite orientation, thus reinforcing each other.<ref name="AutoMK-15" /> Another technology used to overcome thermal effects to allow greater recording densities is [[perpendicular recording]] (PMR), first shipped in 2005,<ref name="AutoMK-16" /> and {{as of|2007|lc=on}}, used in certain HDDs.<ref name="AutoMK-17" /><ref name="AutoMK-18" /><ref name="AutoMK-19" /> Perpendicular recording may be accompanied by changes in the manufacturing of the read/write heads to increase the strength of the magnetic field created by the heads.<ref>{{cite web | url=https://patents.google.com/patent/US20080002290 | title=Damascene coil design for a perpendicular magnetic recording head }}</ref>

In 2004, a higher-density recording media was introduced, consisting of coupled soft and hard magnetic layers. So-called ''[[exchange spring media]]'' magnetic storage technology, also known as ''exchange coupled composite media'', allows good writability due to the write-assist nature of the soft layer. However, the thermal stability is determined only by the hardest layer and not influenced by the soft layer.<ref name=AutoMK-19a /><ref name=AutoMK-19b />

Flux control MAMR (FC-MAMR) allows a hard drive to have increased recording capacity without the need for new hard disk drive platter materials. MAMR hard drives have a microwave-generating spin torque generator (STO) on the read/write heads which allows physically smaller bits to be recorded to the platters, increasing areal density. Normally hard drive recording heads have a pole called a main pole that is used for writing to the platters, and adjacent to this pole is an air gap and a shield. The write coil of the head surrounds the pole. The STO device is placed in the air gap between the pole and the shield to increase the strength of the magnetic field created by the pole; FC-MAMR technically doesn't use microwaves but uses technology employed in MAMR. The STO has a Field Generation Layer (FGL) and a Spin Injection Layer (SIL), and the FGL produces a magnetic field using spin-polarised electrons originating in the SIL, which is a form of spin torque energy.<ref>{{cite web | url=https://blocksandfiles.com/2021/06/14/toshiba-disks-get-2-gen-leg-up-from-flux-control/ | title=Toshiba disks get 2-gen leg-up from flux control | date=June 14, 2021 }}</ref>

=== Components ===
[[File:Hard disk dismantled.jpg|thumb|left|An HDD with disks and motor hub removed, exposing copper-colored stator coils surrounding a bearing in the center of the spindle motor. The orange stripe along the side of the arm is a thin printed-circuit cable, the spindle bearing is in the center and the actuator is in the upper left.]]
[[File:Circuit board of a Samsung hard disk MP0402H.jpg|thumb|right|Circuit board of a 2.5-inch Samsung hard disk MP0402H]]

A typical HDD has two electric motors: a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning disks. The disk motor has an external rotor attached to the disks; the stator windings are fixed in place. Opposite the actuator at the end of the head support arm is the read-write head; thin printed-circuit cables connect the read-write heads to [[amplifier]] electronics mounted at the pivot of the actuator. The head support arm is very light, but also stiff; in modern drives, acceleration at the head reaches 550 [[g-force|''g'']].

[[File:Kopftraeger WD2500JS-00MHB0.jpg|thumb|Head stack with an actuator coil on the left and read/write heads on the right]]
[[File:HDD read-write head.jpg|thumb|Close-up of a single [[disk read-and-write head|read–write head]], showing the side facing the platter]]

The ''{{visible anchor|actuator|Actuator}}'' is a [[permanent magnet]] and [[moving coil]] motor that swings the heads to the desired position. A metal plate supports a squat [[neodymium magnet|neodymium–iron–boron]] (NIB) high-flux [[magnet]]. Beneath this plate is the moving coil, often referred to as the ''[[voice coil]]'' by analogy to the coil in [[loudspeaker]]s, which is attached to the actuator hub, and beneath that is a second NIB magnet, mounted on the bottom plate of the motor (some drives have only one magnet).

The voice coil itself is shaped rather like an arrowhead and is made of doubly coated copper [[magnet wire]]. The inner layer is insulation, and the outer is thermoplastic, which bonds the coil together after it is wound on a form, making it self-supporting. The portions of the coil along the two sides of the arrowhead (which point to the center of the actuator bearing) then interact with the [[magnetic field]] of the fixed magnet. Current flowing radially outward along one side of the arrowhead and radially inward on the other produces the [[magnetic field#Force on a charged particle|tangential force]]. If the magnetic field were uniform, each side would generate opposing forces that would cancel each other out. Therefore, the surface of the magnet is half north pole and half south pole, with the radial dividing line in the middle, causing the two sides of the coil to see opposite magnetic fields and produce forces that add instead of canceling. Currents along the top and bottom of the coil produce radial forces that do not rotate the head.

The HDD's electronics controls the movement of the actuator and the rotation of the disk and transfers data to or from a [[disk controller]]. Feedback of the drive electronics is accomplished by means of special segments of the disk dedicated to [[servomotor|servo]] feedback. These are either complete concentric circles (in the case of dedicated servo technology) or segments interspersed with real data (in the case of embedded servo, otherwise known as sector servo technology). The servo feedback optimizes the signal-to-noise ratio of the GMR sensors by adjusting the voice coil motor to rotate the arm. A more modern servo system also employs milli or micro actuators to more accurately position the read/write heads.<ref>A. Al-Mamun, G. Guo, C. Bi, Hard Disk Drive: Mechatronics and Control, 2006, Taylor & Francis.</ref> The spinning of the disks uses fluid-bearing spindle motors. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media that have failed.

=== {{anchor|ERRORRATESHANDLING}}Error rates and handling ===
Modern drives make extensive use of [[error correction code]]s (ECCs), particularly [[Reed–Solomon error correction]]. These techniques store extra bits, determined by mathematical formulas, for each block of data; the extra bits allow many errors to be corrected invisibly. The extra bits themselves take up space on the HDD, but allow higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage capacity.<ref>{{cite web |url=https://www.karlstechnology.com/blog/hard-drive-error-correcting-code-ecc/ |title=Hard Drive Error Correcting Code (ECC) |publisher=The PC Guide |last=Kozierok |first=Charles |access-date=May 26, 2019 |date=November 25, 2018 |archive-url=https://web.archive.org/web/20190526072642/https://www.karlstechnology.com/blog/hard-drive-error-correcting-code-ecc/ |archive-date=May 26, 2019 |url-status=live }}</ref> For example, a typical 1&nbsp;[[Terabyte|TB]] hard disk with 512-byte sectors provides additional capacity of about 93&nbsp;[[Gibibyte|GB]] for the [[forward error correction|ECC]] data.<ref>{{cite web
 | url = https://www.idema.org/wp-content/uploads/downloads/2011/12/AF-in-Legacy-Infrastructures-SDC2011_IDEMA-AF.pdf
 | title = Advanced Format in Legacy Infrastructures: More Transparent than Disruptive
 | year = 2011
 | access-date = November 5, 2013
 | first = Curtis E.
 | last = Stevens
 | website = idema.org
 | archive-url = https://web.archive.org/web/20131105222506/http://www.idema.org/wp-content/uploads/downloads/2011/12/AF-in-Legacy-Infrastructures-SDC2011_IDEMA-AF.pdf
 | archive-date = November 5, 2013
 | url-status = dead
 }}</ref>

In the newest drives, {{as of|2009|lc=on}},<ref name="AutoMK-21" /> [[low-density parity-check code]]s (LDPC) were supplanting Reed–Solomon; LDPC codes enable performance close to the [[Shannon limit]] and thus provide the highest storage density available.<ref name="AutoMK-21" /><ref>[https://docplayer.net/3699743-2-5-inch-hard-disk-drive-with-high-recording-density-and-high-shock-resistance.html "2.5-inch Hard Disk Drive with High Recording Density and High Shock Resistance] {{Webarchive|url=https://web.archive.org/web/20190526075908/https://docplayer.net/3699743-2-5-inch-hard-disk-drive-with-high-recording-density-and-high-shock-resistance.html |date=May 26, 2019 }}, Toshiba, 2011</ref>

Typical hard disk drives attempt to "remap" the data in a [[Bad sector|physical sector that is failing]] to a spare physical sector provided by the drive's "spare sector pool" (also called "reserve pool"),<ref>{{cite web|author=MjM Data Recovery Ltd |url=http://datarecovery.mjm.co.uk/sectorremapping.html |archive-url=https://web.archive.org/web/20140201174433/http://datarecovery.mjm.co.uk/sectorremapping.html| title=MJM Data Recovery Ltd: Hard Disk Bad Sector Mapping Techniques |website=Datarecovery.mjm.co.uk |access-date=January 21, 2014 | archive-date=February 1, 2014}}</ref> while relying on the ECC to recover stored data while the number of errors in a bad sector is still low enough. The S.M.A.R.T ([[Self-Monitoring, Analysis and Reporting Technology]]) feature counts the total number of errors in the entire HDD fixed by ECC (although not on all hard drives as the related S.M.A.R.T attributes "Hardware ECC Recovered" and "Soft ECC Correction" are not consistently supported), and the total number of performed sector remappings, as the occurrence of many such errors may predict an [[HDD failure]].

The "No-ID Format", developed by IBM in the mid-1990s, contains information about which sectors are bad and where remapped sectors have been located.<ref>{{cite web |url=https://www.karlstechnology.com/blog/hard-drive-sector-format-and-structure/ |title=Hard Drive Sector Format and Structure |publisher=The PC Guide |last=Kozierok |first=Charles |access-date=May 26, 2019 |date=December 23, 2018 |archive-url=https://web.archive.org/web/20190526072622/https://www.karlstechnology.com/blog/hard-drive-sector-format-and-structure/ |archive-date=May 26, 2019 |url-status=live }}</ref>

Only a tiny fraction of the detected errors end up as not correctable. Examples of specified uncorrected bit read error rates include:
* 2013 specifications for enterprise SAS disk drives state the error rate to be one uncorrected bit read error in every 10<sup>16</sup> bits read,<ref name="SGAT2013">{{cite web
 | url = https://www.seagate.com/files/www-content/product-content/savvio-fam/enterprise-performance-15k-hdd/savvio-15k-4/en-us/enterprise-performance-15k-hdd-ds1797-1-1307us.pdf
 | title = Enterprise Performance 15K HDD: Data Sheet
 | year = 2013
 | access-date = October 24, 2013
 | publisher = Seagate
 | archive-url = https://web.archive.org/web/20131029192706/http://www.seagate.com/files/www-content/product-content/savvio-fam/enterprise-performance-15k-hdd/savvio-15k-4/en-us/enterprise-performance-15k-hdd-ds1797-1-1307us.pdf
 | archive-date = October 29, 2013
 | url-status = live
 }}</ref><ref name="WD2013">{{cite web
 | url = https://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-771463.pdf
 | title = WD Xe: Datacenter hard drives
 | year = 2013
 | access-date = October 24, 2013
 | publisher = Western Digital
 | archive-url = https://web.archive.org/web/20131029193439/http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-771463.pdf
 | archive-date = October 29, 2013
 | url-status = live
 }}</ref> 
* 2018 specifications for consumer SATA hard drives state the error rate to be one uncorrected bit read error in every 10<sup>14</sup> bits.<ref name="SGAT2018">{{cite web
 | title = 3.5" BarraCuda data sheet
 | publisher = Seagate
 | date = June 2018
 | url = https://www.seagate.com/www-content/datasheets/pdfs/3-5-barracudaDS1900-11-1806US-en_US.pdf
 | access-date = July 28, 2018
 | archive-url = https://web.archive.org/web/20180728070449/https://www.seagate.com/www-content/datasheets/pdfs/3-5-barracudaDS1900-11-1806US-en_US.pdf
 | archive-date = July 28, 2018
 | url-status = live
 }}</ref><ref name="WD2018">{{cite web
 | title = WD Red Desktop/Mobile Series Spec Sheet
 | publisher = Western Digital
 | date = April 2018
 | url = https://www.wdc.com/content/dam/wdc/website/downloadable_assets/eng/spec_data_sheet/2879-800002.pdf
 | access-date = July 28, 2018
 | archive-url = https://web.archive.org/web/20180728070730/https://www.wdc.com/content/dam/wdc/website/downloadable_assets/eng/spec_data_sheet/2879-800002.pdf
 | archive-date = July 28, 2018
 | url-status = live
 }}</ref>
Within a given manufacturers model the uncorrected bit error rate is typically the same regardless of capacity of the drive.<ref name="SGAT2013" /><ref name="WD2013" /><ref name="SGAT2018" /><ref name="WD2018" />

The worst type of errors are [[silent data corruption]]s which are errors undetected by the disk firmware or the host operating system; some of these errors may be caused by hard disk drive malfunctions while others originate elsewhere in the connection between the drive and the host.<ref>{{Cite news |title= Keeping Bits Safe: How Hard Can It Be? |work= ACM Queue |date= October 1, 2010 |author= David S. H. Rosenthal |url= https://queue.acm.org/detail.cfm?id=1866298 |access-date= January 2, 2014 |author-link= David S. H. Rosenthal |archive-url= https://web.archive.org/web/20131217020947/http://queue.acm.org/detail.cfm?id=1866298 |archive-date= December 17, 2013 |url-status= live }}</ref>

{{Anchor|TDMR}}

=== Development ===
[[File:Full History Disk Areal Density Trend.png|thumb|Leading-edge hard disk drive [[Density (computer storage)|areal densities]] from 1956 through 2009 compared to [[Moore's law]]. By 2016, progress had slowed significantly below the extrapolated density trend.<ref name="Hayes 2016">{{cite web |url=http://bit-player.org/2016/wheres-my-petabyte-disk-drive |title= Where's My Petabyte Disk Drive? |first= Brian |last= Hayes|page= chart of historical data courtesy of Edward Grochowski  |date= March 27, 2016 |access-date= December 1, 2019 }}</ref>]]

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.<ref name="Byrne2015b">{{cite web |url=http://www.federalreserve.gov/econresdata/notes/feds-notes/2015/prices-for-data-storage-equipment-and-the-state-of-it-innovation-20150701.html#fn2 |title=Prices for Data Storage Equipment and the State of IT Innovation |publisher=The Federal Reserve Board FEDS Notes |first=David |last=Byrne |page=Table 2 |date=July 1, 2015 |access-date=July 5, 2015 |archive-url=https://web.archive.org/web/20150708124555/http://www.federalreserve.gov/econresdata/notes/feds-notes/2015/prices-for-data-storage-equipment-and-the-state-of-it-innovation-20150701.html#fn2 |archive-date=July 8, 2015 |url-status=live }}</ref> Speaking in 1997, [[Gordon Moore]] called the increase "flabbergasting",<ref name="Moore1997">{{cite news
 | url = https://www.pcmag.com/article2/0,2817,1172800,00.asp
 | title = Gallium Arsenide
 | work = PC Magazine
 | date = March 25, 1997
 | quote = Gordon Moore: ... the ability of the magnetic disk people to continue to increase the density is flabbergasting--that has moved at least as fast as the semiconductor complexity.
 | access-date = August 16, 2014
 | archive-url = https://web.archive.org/web/20140821103700/http://www.pcmag.com/article2/0,2817,1172800,00.asp
 | archive-date = August 21, 2014
 | url-status = live
 }}</ref> while observing later that growth cannot continue forever.<ref name="Moore2005">{{cite news |last=Dubash |first=Manek |url=http://www.techworld.com/news/operating-systems/moores-law-is-dead-says-gordon-moore-3576581/ |title=Moore's Law is dead, says Gordon Moore |work=techworld.com |date=April 13, 2005 |url-status=dead |archive-url=https://web.archive.org/web/20140706081110/http://news.techworld.com/operating-systems/3477/moores-law-is-dead-says-gordon-moore/ |archive-date=July 6, 2014 |access-date=March 18, 2022 |quote=It can't continue forever. The nature of exponentials is that you push them out and eventually disaster happens. }}</ref> Price improvement decelerated to −12% per year during 2010–2017,<ref name="McCallum">{{cite web |title=Disk Drive Prices (1955–2017) |url=http://www.jcmit.net/diskprice.htm |year=2017 |first=John C. |last=McCallum |access-date=July 15, 2017 |archive-url=https://web.archive.org/web/20170711202719/http://www.jcmit.net/diskprice.htm |archive-date=July 11, 2017 |url-status=live }}</ref> as the growth of areal density slowed. The rate of advancement for areal density slowed to 10% per year during 2010–2016,<ref name="IBM Fontana 2016">{{cite web |url=http://www.ibmsystemsmag.com/mainframe/storage/Support/cloud-trends-projections/?page=1 |title=A Look at Cloud Storage Component Technologies Trends and Future Projections |first1=Gary M. |last1=Decad |author2=Robert E. Fontana Jr. |website=ibmsystemsmag.com |date=July 6, 2017 |access-date=July 21, 2014 |page=Table 1 |archive-url=https://web.archive.org/web/20170729050933/http://ibmsystemsmag.com/mainframe/storage/support/cloud-trends-projections/?page=1 |archive-date=July 29, 2017 |url-status=dead }}</ref> and there was difficulty in migrating from perpendicular recording to newer technologies.<ref name="Mellor 2014-11-10">{{cite news |last=Mellor |first=Chris |url=https://www.theregister.co.uk/2014/11/10/kryders_law_of_ever_cheaper_storage_disproven/ |title=Kryder's law craps out: Race to UBER-CHEAP STORAGE is OVER |work=theregister.co.uk |location=UK |publisher=The Register |date=November 10, 2014 |access-date=November 12, 2014 |quote=The 2011 Thai floods almost doubled disk capacity cost/GB for a while. Rosenthal writes: 'The technical difficulties of migrating from PMR to HAMR, meant that already in 2010 the Kryder rate had slowed significantly and was not expected to return to its trend in the near future. The floods reinforced this.' |archive-url=https://web.archive.org/web/20141112004831/http://www.theregister.co.uk/2014/11/10/kryders_law_of_ever_cheaper_storage_disproven/ |archive-date=November 12, 2014 |url-status=live }}</ref>

As bit cell size decreases, more data can be put onto a single drive platter. In 2013, a production desktop 3&nbsp;TB HDD (with four platters) would have had an areal density of about 500&nbsp;Gbit/in<sup>2</sup> which would have amounted to a bit cell comprising about 18 magnetic grains (11 by 1.6 grains).<ref name="Anderson2013a" >{{cite web | url = https://www.dtc.umn.edu/resources/bd2013_anderson.pdf | title = HDD Opportunities & Challenges, Now to 2020 | year = 2013 | access-date = May 23, 2014 | quote = 'PMR CAGR slowing from historical 40+% down to ~8-12%' and 'HAMR CAGR = 20-40% for 2015–2020' | first = Dave | last = Anderson | publisher = Seagate | archive-url = https://web.archive.org/web/20140525232605/https://www.dtc.umn.edu/resources/bd2013_anderson.pdf | archive-date = May 25, 2014 | url-status = live }}</ref> Since the mid-2000s, areal density progress has been challenged by a [[Superparamagnetism#Effect on hard drives|superparamagnetic]] trilemma involving grain size, grain magnetic strength and ability of the head to write.<ref>{{cite journal
| title = New Paradigms in Magnetic Recording
| last = Plumer |display-authors=etal 
| first = Martin L.
| journal = Physics in Canada
| volume = 67
| issue = 1
| date = March 2011
| pages = 25–29
|arxiv = 1201.5543| bibcode = 2012arXiv1201.5543P }}</ref> 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 drive]]s (SSDs). In 2013, [[Seagate Technology|Seagate]] introduced [[shingled magnetic recording]] (SMR),<ref name="Seagate 2013-09-09">{{cite press release |url=http://www.seagate.com/about/newsroom/press-releases/shingled-magnetic-recording-milestone-pr-master/ |archive-url=https://web.archive.org/web/20141009135540/http://www.seagate.com/about/newsroom/press-releases/shingled-magnetic-recording-milestone-pr-master/ |title=Seagate Delivers On Technology Milestone: First to Ship Hard Drives Using Next-Generation Shingled Magnetic Recording |location=New York |publisher=[[Seagate Technology]] plc |date=September 9, 2013 |access-date=July 5, 2014 |archive-date=October 9, 2014 |quote=Shingled Magnetic Technology is the First Step to Reaching a 20 Terabyte Hard Drive by 2020}}</ref> intended as something of a "stopgap" technology between PMR and Seagate's intended successor [[heat-assisted magnetic recording]] (HAMR). SMR utilizes 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).<ref>{{cite web
 | url = https://lwn.net/Articles/591782/
 | title = Support for shingled magnetic recording devices
 | date = March 26, 2014
 | access-date = January 7, 2015
 | first = Jake
 | last = Edge
 | publisher = [[LWN.net]]
 | archive-url = https://web.archive.org/web/20150202075938/http://lwn.net/Articles/591782/
 | archive-date = February 2, 2015
 | url-status = live
 }}</ref><ref>{{cite web
 | url = https://lwn.net/Articles/548116/
 | title = LSFMM: A storage technology update
 | date = April 23, 2013
 | access-date = January 7, 2015
 | first = Jonathan
 | last = Corbet
 | publisher = [[LWN.net]]
 | quote = A 'shingled magnetic recording' (SMR) drive is a rotating drive that packs its tracks so closely that one track cannot be overwritten without destroying the neighboring tracks as well. The result is that overwriting data requires rewriting the entire set of closely-spaced tracks; that is an expensive tradeoff, but the benefit—much higher storage density—is deemed to be worth the cost in some situations.
 | archive-url = https://web.archive.org/web/20150107075254/https://lwn.net/Articles/548116/
 | archive-date = January 7, 2015
 | url-status = live
 }}</ref>

By contrast, [[HGST]] (now part of [[Western Digital]]) focused on developing ways to seal [[helium]]-filled drives instead of the usual filtered air. Since [[turbulence]] and [[friction]] are reduced, higher areal densities can be achieved due to using a smaller track width, and the energy dissipated due to friction is lower as well, resulting in a lower power draw. Furthermore, more platters can be fit into the same enclosure space, although helium gas is notoriously difficult to prevent escaping.<ref>{{Cite web|date=2020|title=Brochure: HelioSeal Technology: Beyond Air. Helium Takes You Higher.|url=https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/western-digital/collateral/brochure/brochure-helioseal-technology.pdf|website=Western Digital}}</ref> Thus, helium drives are completely sealed and do not have a breather port, unlike their air-filled counterparts.

Other recording technologies are either under research or have been commercially implemented to increase areal density, 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.<ref name="Shilov_anandtech_b">{{cite news |url=http://www.anandtech.com/show/9866/hard-disk-drives-with-hamr-technology-set-to-arrive-in-2018 |title=Hard Disk Drives with HAMR Technology Set to Arrive in 2018 |first=Anton |last=Shilov |date=December 18, 2015 |access-date=January 2, 2016 |quote=Unfortunately, mass production of actual hard drives featuring HAMR has been delayed for a number of times already and now it turns out that the first HAMR-based HDDs are due in 2018. ... HAMR HDDs will feature a new architecture, require new media, completely redesigned read/write heads with a laser as well as a special near-field optical transducer (NFT) and a number of other components not used or mass produced today. |archive-url=https://web.archive.org/web/20160102200055/http://www.anandtech.com/show/9866/hard-disk-drives-with-hamr-technology-set-to-arrive-in-2018 |archive-date=January 2, 2016 |url-status=live }}</ref> HAMR is expected to ship commercially in late 2024,<!-- did it ship? --><ref>{{cite web |url= https://www.tomshardware.com/news/seagate-reveals-hamr-roadmap-32-tb-comes-first |title= Seagate Reveals HAMR HDD Roadmap: 32TB First, 40TB Follows |last= Shilov |first= Anton |date= June 8, 2023 |access-date= Oct 3, 2024 }}</ref> after technical issues delayed its introduction by more than a decade, from earlier projections as early as 2009.<ref name= "HAMR 2008 for 2009" >{{cite web |url= https://blog.dshr.org/2018/05/longer-talk-at-msst2018.html |title= Longer talk at MSST2018 |last= Rosenthal |first= David |date= May 16, 2018 |access-date= November 22, 2019 }}</ref><ref name= "HAMR 2014 for 2015" >{{cite web |url= https://www.kitguru.net/components/hard-drives/anton-shilov/tdk-hamr-technology-could-enable-15tb-hard-drives-already-in-2015/ |title= TDK: HAMR technology could enable 15TB HDDs already in 2015 |last= Shilov |first= Anton |date= October 15, 2014 |access-date= November 15, 2019 }}</ref><ref name= "HAMR 2013 for 2016" >{{cite web |url= http://www.tomsitpro.com/articles/wd-hamr-hdd-heat-assisted-magnetic-recording,1-1396.html |title= WD Demos Future HDD Storage Tech: 60TB Hard Drives |last= Oliver |first= Bill |work= Tom's IT Pro |quote= …Seagate expects to start selling HAMR drives in 2016. |date= November 18, 2013 |access-date= November 15, 2019 |archive-url= https://web.archive.org/web/20131121065015/http://www.tomsitpro.com/articles/wd-hamr-hdd-heat-assisted-magnetic-recording,1-1396.html |archive-date= November 21, 2013 }}</ref><ref name= "blocks HAMR 2019" >{{cite web |url= https://blocksandfiles.com/2019/08/28/nearline-disk-drives-ssd-attack/ |title= How long before SSDs replace nearline disk drives? |last= Mellor |first= Chris |quote= Seagate CTO Dr John Morris told analysts that Seagate has built 55,000 HAMR drives and aims to get disks ready for customer sampling by the end of 2020. |date= August 28, 2019 |access-date= November 15, 2019 }}</ref> HAMR's planned successor, [[bit-patterned recording]] (BPR),<ref name="AutoMK-22" /> has been removed from the roadmaps of Western Digital and Seagate.<ref name= "BPR roadmaps 2018" >{{cite web |url= https://blog.dshr.org/2018/05/longer-talk-at-msst2018.html |title= Longer talk at MSST2018 |last= Rosenthal |first= David |quote= The most recent Seagate roadmap pushes HAMR shipments into 2020, so they are now slipping faster than real-time. Western Digital has given up on HAMR and is promising that Microwave Assisted Magnetic Recording (MAMR) is only a year out. BPM has dropped off both companies' roadmaps. |date= May 16, 2018 |access-date= November 22, 2019 }}</ref> Western Digital's microwave-assisted magnetic recording (MAMR),<ref>{{cite journal |last=Mallary |display-authors=etal |first= Mike|date=July 2014 |title= Head and Media Challenges for 3 Tb/in<sup>2</sup> Microwave-Assisted Magnetic Recording|journal=IEEE Transactions on Magnetics |volume=50 |issue=7 |pages=1–8 |doi=10.1109/TMAG.2014.2305693|s2cid=22858444 |issn = 0018-9464 }}</ref><ref>{{cite journal|last1=Li|first1=Shaojing|last2=Livshitz|first2=Boris|last3=Bertram|first3=H. Neal|last4=Schabes|first4=Manfred|last5=Schrefl|first5=Thomas|last6=Fullerton|first6=Eric E.|last7=Lomakin|first7=Vitaliy|title=Microwave assisted magnetization reversal in composite media|journal=Applied Physics Letters|date=2009|volume=94|issue=20|page=202509|doi=10.1063/1.3133354|url=https://www.karlstechnology.com/hard-drives/JAP_2009_MAMR.pdf|bibcode=2009ApPhL..94t2509L|access-date=May 24, 2019|archive-url=https://web.archive.org/web/20190524225721/https://www.karlstechnology.com/hard-drives/JAP_2009_MAMR.pdf|archive-date=May 24, 2019|url-status=live}}</ref> also referred to as energy-assisted magnetic recording (EAMR), was sampled in 2020, with the first EAMR drive, the Ultrastar HC550, shipping in late 2020.<ref>{{Cite web|last=Shilov|first=Anton|title=Western Digital Reveals 18 TB DC HC550 'EAMR' Hard Drive|url=https://www.anandtech.com/show/14869/western-digital-announces-18-tb-eamr-hard-drive |date=September 18, 2019 |access-date=2021-10-11|website=AnandTech}}</ref><ref name="Blocks MAMR 2019">{{cite web |url= https://blocksandfiles.com/2019/09/03/western-digital-18tb-and-20tb-mamr-disk-drives/ |website=Blocks & Files |title= Western Digital debuts 18TB and 20TB MAMR disk drives |last= Mellor |first= Chris |quote= …microwave-assisted magnetic (MAMR) recording technology…sample shipments are due by the end of the year. |date= September 3, 2019 |access-date= November 23, 2019 }}</ref><ref>{{Cite web|last=Raevenlord |title=Western Digital Finally Launches Ultrastar DC HC550 18 TB Drives With EAMR for Enterprise|url=https://www.techpowerup.com/269562/western-digital-finally-launches-ultrastar-dc-hc550-18-tb-drives-with-eamr-for-enterprise|access-date=2021-10-11|website=TechPowerUp|date=July 8, 2020 |language=en}}</ref> [[Two-dimensional magnetic recording]] (TDMR)<ref name="Anderson2013a" /><ref name="Wood 2010">{{cite web |url=https://www.ewh.ieee.org/r6/scv/mag/MtgSum/Meeting2010_10_Presentation.pdf |title=Shingled Magnetic Recording and Two-Dimensional Magnetic Recording |last=Wood |first=Roger |work=[[IEEE]] |publisher=Hitachi GST |date=October 19, 2010 |access-date=August 4, 2014 |archive-url=https://web.archive.org/web/20140810161542/http://www.ewh.ieee.org/r6/scv/mag/MtgSum/Meeting2010_10_Presentation.pdf |archive-date=August 10, 2014 |url-status=live }}</ref> and "current perpendicular to plane" [[giant magnetoresistance]] (CPP/GMR) heads have appeared in research papers.<ref name="Coughlin" /><ref>{{Cite arXiv |title=All-Heusler giant-magnetoresistance junctions with matched energy bands and Fermi surfaces |eprint = 1301.6106|last1 = Bai|first1 = Zhaoqiang|last2 = Cai|first2 = Yongqing|last3 = Shen|first3 = Lei|last4 = Han|first4 = Guchang|last5 = Feng|first5 = Yuanping|year = 2013|class = cond-mat.mes-hall}}</ref><ref>{{cite web|url=http://www1.hgst.com/hdd/research/recording_head/pr/PerpendicularAnimation.html|title=Perpendicular Magnetic Recording Explained - Animation|date=December 21, 2001 |access-date=July 27, 2014|archive-url=https://web.archive.org/web/20181006062214/http://www1.hgst.com/hdd/research/recording_head/pr/PerpendicularAnimation.html|archive-date=October 6, 2018|url-status=live}}</ref>

Some drives have adopted dual independent actuator arms to increase read/write speeds and compete with SSDs.<ref>{{cite web |url=https://www.anandtech.com/show/13935/seagate-hdd-plans-2019 |title= State of the Union: Seagate's HAMR Hard Drives, Dual-Actuator Mach2, and 24 TB HDDs on Track |work=Anandtech.com |access-date=February 20, 2019 |archive-url=https://web.archive.org/web/20190220002907/https://www.anandtech.com/show/13935/seagate-hdd-plans-2019 |archive-date=February 20, 2019 |url-status=live }}</ref>
A 3D-actuated vacuum drive (3DHD) concept<ref name= "3DHD blog" >{{Cite web |url= https://blog.dshr.org/2019/09/promising-new-hard-disk-technology.html |title= Promising New Hard Disk Technology |access-date= December 1, 2019 }}</ref><!--3DHD is developed by L2 drive--> and 3D magnetic recording have been proposed.<ref>{{Cite web|url=https://www.extremetech.com/extreme/168619-3d-magnetic-storage-breakthrough-enables-100tb-hard-drives|title=3D magnetic storage breakthrough enables 100TB+ hard drives &#124; Extremetech|date=October 15, 2013 }}</ref>

Depending upon assumptions on feasibility and timing of these technologies, Seagate forecasts that areal density will grow 20% per year during 2020–2034.<ref name= "blocks WWrevenue August2019"/>