Perpendicular recording

Perpendicular recording (or Perpendicular Magnetic Recording, PMR) is a technology for data recording on hard disks. It was first proven advantageous in 1976 by Shun-ichi Iwasaki, then professor of the Tohoku University in Japan, and first commercially implemented in 2005.

Advantages

Perpendicular recording is forecast to be capable of delivering more than triple the storage density of traditional longitudinal recording [http://www.eetimes.com/showArticle.jhtml?articleID=171200282&pgno=2] . There was some interest in using the system in floppy disks in the 1980s, but the technology was never reliable. Today there is renewed interest in using it for hard drives, which are rapidly reaching the limits of longitudinal recording. Current hard disk technology with longitudinal recording has an estimated limit of 100 to 200 gigabit per square inch due to the superparamagnetic effect, though this estimate is constantly changing. Perpendicular recording is predicted to allow information densities of up to around 1 Tbit/sq. inch (1000 Gbit/sq. inch). [http://www.hitachi.com/New/cnews/071015a.html Hitachi News Release - Hitachi achieves nanotechnology milestone for quadrupling terabyte hard drive] ]

Technology

The main challenge in designing magnetic information storage media is to retain the magnetization of the medium despite thermal fluctuations caused by the superparamagnetic limit. If the thermal energy is too high, there may be enough energy to reverse the magnetization in a region of the medium, destroying the data stored there. The energy required to reverse the magnetization of a magnetic region is proportional to the size of the magnetic region and the magnetic coercivity of the material. The larger the magnetic region is and the higher the magnetic coercivity of the material, the more stable the medium is. There is a minimum size for a magnetic region at a given temperature and coercivity. If it is any smaller it is likely to be spontaneously de-magnetized by local thermal fluctuations. Perpendicular recording uses higher coercivity material because the head's write field penetrates the medium more efficiently in the perpendicular geometry.

The popular explanation for the advantage of perpendicular recording is that it achieves higher storage densities by aligning the poles of the magnetic elements, which represent bits, perpendicularly to the surface of the disk platter, as shown in the illustration. In this not-quite-accurate explanation, aligning the bits in this manner takes less platter than what would have been required had they been placed longitudinally so they can be placed closer together on the platter, thus increasing the number of magnetic elements that can be stored in a given area. The true picture is a bit more complex, having to do with the use of a magnetically "stronger" (higher coercivity) material as the storage medium. This is possible because in a perpendicular arrangement the magnetic flux is guided through a magnetically soft (and relatively thick) underlayer underneath the hard magnetic media films (considerably complicating and thickening the total disk structure). This magnetically soft underlayer can be effectively considered a part of the write head, making the write head more efficient, thus making it possible to produce a stronger write field gradient with essentially the same head materials as for longitudinal heads, and therefore allowing for the use of the higher coercivity magnetic storage medium. A higher coercivity medium is inherently thermally more stable, as stability is proportional to the product of bit (or magnetic grain) volume times the "uniaxial anisotropy constant" K_u, which in turn is higher for a material with a higher magnetic coercivity.

To achieve higher levels of areal density (usually expressed as the amount of data that can be placed in a square inch on a disk), drive manufacturers place bits perpendicular to the disk platter, rather than laying them flat as in longitudinal recording. In longitudinal recording the bits can be further shrunk, but the smaller they are the more susceptible they are to erasure from thermal energy.

Implementations

Toshiba was the first company to make a commercially available disk drive (1.8") using this technology in 2005 [http://www.toshiba.co.jp/about/press/2004_12/pr1401.htm First Perpendicular Recording HDD - Toshiba Press Release] ] . The product is said to have suffered reliability setbacks in the consumer market. In January 2006, Seagate Technology began shipping its first laptop sized, 2.5 inch hard drive using perpendicular recording technology, the Seagate Momentus 5400.3. Seagate also announced at that time that the majority of its hard disk storage devices would utilize the new technology by the end of 2006. Other HDD manufacturers are also expected to adopt this technology rapidly.

In April 2006, Seagate began shipping the world's first 3.5 inch perpendicular recording hard drive, the Cheetah 15K.5, which provides up to 300GB storage. The drives run at 15,000 rpm and claim to offer 30% better performance than their predecessors with a data rate of 73-125 Mbyte/s. [http://www.seagate.com/docs/pdf/datasheet/disc/ds_cheetah_15k_5.pdf Seagate Cheetah 15K.5 Datasheet] ]

Also in April 2006, Seagate announced the availability of Barracuda 7200.10, a series of convert|3.5|in|mm|sing=on HDDs utilizing perpendicular recording with a maximum capacity of 750 GB. Drives began shipping in late April 2006.

Hitachi promised a 20 GB Microdrive. Hitachi's first laptop drive (2.5-inch) based on perpendicular recording became available in mid-2006, featuring a maximum capacity of 160 GB.

In June 2006, Toshiba announced a convert|2.5|in|mm|sing=on hard drive of 200-GB capacity with mass production starting in August, effectively raising the bar on mobile storage.

In July 2006, Western Digital announced it is in volume production of its next-generation WD Scorpio convert|2.5|in|mm|sing=on hard drives using WD-designed and manufactured perpendicular magnetic recording (PMR) technology to achieve 80 GB-per-platter density. [http://www.westerndigital.com/en/company/releases/PressRelease.asp?release={774FADA9-FCD1-4028-BF32-A7F536029C85} WD IN VOLUME PRODUCTION OF 80 GB-PER-PLATTER MOBILE HARD DRIVES USING PERPENDICULAR MAGNETIC RECORDING TECHNOLOGY ] ]

In August 2006 Fujitsu extended its convert|2.5|in|mm|sing=on lineup to include SATA models utilizing perpendicular recording, offering up to 160GB capacity.

In December 2006 Toshiba said the new 100GB two-platter HDD is based on perpendicular magnetic recording (PMR) and was designed in the "short" 1.8-inch form factor. [http://www.appleinsider.com/article.php?id=2281 AppleInsider | Briefly: Foxconn to build 1.5m MBPs; 100GB iPod drive ] ]

In December 2006 Fujitsu announced the global launch of its MHX2300BT series of convert|2.5|in|mm|sing=on hard disk drives, with capacities of 250 and 300 GB.

In January 2007 Hitachi announced the first 1 Terabyte Hard Drive [http://www.pcworld.com/article/id,128400-page,1/article.html PC World - Hitachi Introduces 1-Terabyte Hard Drive ] ] using the technology, which they then delivered in April 2007 [http://www.engadget.com/2007/04/25/hitachi-gets-its-one-terabyte-deskstar-7k1000-drives-out-the-doo Hitachi gets its one terabyte Deskstar 7K1000 drives out the door - Engadget ] ]

In July 2008 Seagate Technology announced a 1.5 Terabyte Hard Drive [ [http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9109018 Seagate unveils world's first 1.5TB desktop drive ] ] using PMR technology. This represents the biggest jump in hard drive storage capacity in the last 50 years of hard drive technology.

References

External links

* [http://www.magneticdiskheritagecenter.org/MDHC/NAPMRC_HOAGLAND.pdf Magnetic Disk History] History of Magnetic Disk Storage Based on Perpendicular Magnetic Recording
* [http://www.hitachigst.com/hdd/hddpdf/tech/chart13.pdf High-resolution graphic]
* [http://www.hitachigst.com/hdd/research/recording_head/pr/ Hitachi Research page]
* [http://www.hitachigst.com/hdd/research/recording_head/pr/PerpendicularAnimation.html "Get Perpendicular"] A Flash animation and song explaining perpendicular recording from Hitachi Research
* [http://www.harddiskdriverevolution.com/perpendicular.html "Perpendicular"] video from Toshiba Storage Device Division demonstrating PMR functionality
* [http://www.trixsrt.com/srttechnology.htm "Signal Representation Technology (SRT)"] : an alternative to digital recording with potential gains of over eight times that of traditional storage technology
*Perpendicular Magnetic Recording (Hardcover) by Sakhrat Khizroev, Dmitri Litvinov: ISBN 1-4020-2662-5
* [http://www.thailand4.com/news/2007-05-15/1500-photo-release-pmr-inventor-sees-result-of-life/ Photo Release: PMR Inventor Sees Result of Life's Work] : Shun-ichi Iwasaki at his first visit at Hitachi's manufacturing facility in Prachinburi, Thailand
*http://www.infostor.com/display_article/245676/23/ARCHI/none/none/1/Seagate-goes-perpendicular/