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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 of 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 has 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,〔(【引用サイトリンク】title=TDK: HAMR technology could enable 15TB HDDs already in 2015 )〕 and in December 2014 Seagate stated that it expected to produce working prototype drives during 2015 with commercial production anticipated in 2016.〔(【引用サイトリンク】title=Seagate to release 10TB hard disk drive next year )〕 ==Overview== 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heat-assisted magnetic recording」の詳細全文を読む スポンサード リンク
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