Heat-assisted magnetic recording
Heat-assisted magnetic recording (HAMR) is a magnetic storage technology for hard drives in which a small laser is used to heat the part of the disk that is being written to. The heat changes the magnetic properties (its "coercivity") of the disk for a short time, reducing or removing the superparamagnetic effect while writing takes place. This magnetic effect sets a limit on the areal density of magnetic recording (how much data can be stored in a given area of a disk). The effect of HAMR is to allow writing on a much smaller scale than before, greatly increasing the amount of data that can be held on a standard disk platter.
The technology was initially seen as extremely difficult to achieve, with doubts expressed about its feasibility. As at 2014, no hard disks using HAMR are currently on the market, but HAMR is in an advanced state of development with demonstration drives produced by companies such as Seagate. A spokesperson for TDK, who have demonstrated read/write heads supporting HAMR, stated in October 2014 that the technology could appear in commercial hard drives by late 2015 to early 2016, and in December 2014 Seagate stated that it expected to produce working prototype drives during 2015 with commercial production anticipated in 2016.
There have been a series of technologies developed to allow hard drives to increase in capacity with little effect on cost; one of the latest is perpendicular recording. To go beyond the limits of perpendicular recording, new technologies are being developed, including helium-filled drives, shingled magnetic recording (SMR), as well as heat-assisted magnetic recording ("HAMR").
The limitation of perpendicular recording is often characterised by the competing requirements of Readability, Writeability and Stability commonly known as the Magnetic Recording Trilemma. HAMR is one technique proposed to break the trilemma and produce a workable solution. The problem is that to store data reliably for very small bit sizes the magnetic medium must be made of a material with a very high coercivity. At increasing areal densities, the size occupied by one bit is so small, and the coercivity required becomes so high, that the magnetic field able to be created for writing data cannot be made strong enough to permanently affect the data (because it is not possible to produce a more powerful magnetic field in the smaller space available using existing methods). In effect, a point exists at which it becomes impractical or impossible to make a working disk drive because magnetic writing activity is no longer viable.
Coercivity happens to be temperature dependent. If the temperature rises then the coercivity would be lower. HAMR uses this physical behavior to solve the problem. In HAMR, a small laser is used to temporarily spot-heat the tiny area being written to at any given time. When the temperature of the area being written is raised in this way above the Curie temperature, the magnetic medium effectively loses much of its coercivity, so a realistically achievable magnetic write field can write data to the medium. As only a tiny part of the disk is heated at a time, the heated part cools very quickly, and comparatively little power is needed.
HAMR could eventually increase the limit of magnetic recording by more than a factor of 100. This could result in storage capacities as great as 50 terabits per square inch. Running costs are not expected to differ significantly from non-HAMR drives, since the laser only uses a few tens of milliwatts (around 1% of the common 5 to 12 watts in active use of large 3.5 inch HDDs). It competes with technologies such as SMR.
Industry observer IDC stated in 2013 that ""The technology is very, very difficult, and there has been a lot of skepticism if it will ever make it into commercial products", with opinions generally that HAMR is unlikely to be commercially available before 2017. Seagate commented that the challenges include "attaching and aligning a semiconductor diode laser to an HDD write head and implementing near-field optics to deliver the heat", along with the scale of use which is far greater than previous near-field optic uses.
- In 1954, engineers of PL Corp working for RCA filed a patent which described the basic principle of using heat in conjunction with a magnetic field to record data. This was followed by many other patents in this area with the initial focus on tape storage.
- In the 1980s, a class of mass storage device called the magneto-optical drive became commercially available which used essentially the same technique for writing data to a disk. One advantage of magneto-optic recording over purely magnetic storage at that time was that the bit size was defined by the size of the focused laser spot rather than the magnetic field. In 1988, a 5.25-inch magneto-optic disk could hold 650 megabytes of data with a roadmap to several gigabytes; a single 5.25" magnetic disk had a capacity of around 100 megabytes.
- In late 1992, Sony introduced MiniDisc, a music recording and playback format intended to replace audio cassettes. Recordable MiniDiscs used heat-assisted magnetic recording but the discs were read optically via the Faraday effect.
- 2006 - Fujitsu demonstrates HAMR.
- As of 2007, Seagate believed it could produce 300 terabit (37.5 terabyte) Hard disk drives using HAMR technology. Some news sites erroneously reported that Seagate would launch a 300 TB HDD by 2010. Seagate responded to this news stating that 50 terabit per-square-inch density is well past the 2010 timeframe and that this may also involve a combination of Bit Patterned Media.
- In early 2009 Seagate achieved 250 Gb per square inch using HAMR. This was half of the density achieved via perpendicular recording at that time.
- Hard disk technology progressed rapidly and as of January 2012, desktop hard disk drives typically had a capacity of 500 to 2000 gigabytes, while the largest-capacity drives were 4 terabytes. It was recognised as early as 2000  that the then current technology for hard disk drives would have limitations and that heat-assisted recording was one option to extend the storage capacity.
- In March 2012 Seagate became the first hard drive maker to achieve the milestone storage density of 1 terabit per square inch using HAMR technology.
- In October 2012 TDK announced that they had reached a storage density of 1.5 terabit per square inch, using HAMR. This corresponds to 2TB per platter in a 3.5" drive.
- November 2013 - Western Digital demonstrates a working HAMR drive, although not yet ready for commercial sales, and Seagate state they expect to begins selling HAMR based drives around 2016.
- In May 2014, Seagate said they planned to produce low quantities of 6 to 10TB capacity hard disks in the "near future", but that this would require "a lot of technical investment as you know, it’s also a lot of test investment". Though Seagate has not stated that the new hard disks would use HAMR, bit-tech.net speculates that they will. Seagate started shipping 8TB drives around July 2014, but without saying how that capacity was reached; extremetech.com speculates that shingled magnetic recording was used rather than HAMR.
- In October 2014, TDK, who supply hard drive components to the major hard drive manufacturers, stated that HAMR drives up to around 15TB would probably start to become available by 2016, and that the results from a prototype 10,000 rpm Seagate hard drive with a TDK HAMR head suggested that the standard 5 year durability required by enterprise customers was also achievable.
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