Two-dimensional magnetic recording

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General concept for TDMR using multiple read elements TDMR Concept.jpg
General concept for TDMR using multiple read elements

Two-dimensional magnetic recording (TDMR) is a technology introduced in 2017 in hard disk drives (HDD) used for computer data storage. Most of the world's data is recorded on HDDs, and there is continuous pressure on manufacturers to create greater data storage capacity in a given HDD form-factor and for a given cost. In an HDD, data is stored using magnetic recording on a rotating magnetic disk and is accessed through a write-head and read-head (or read-element). TDMR allows greater storage capacity by advantageously combining signals simultaneously from multiple read-back heads to enhance the recovery of one or more data-tracks. In this manner, data can be stored with higher areal-density on the disks thus providing higher capacity in each HDD. [1] [2] [3] TDMR is a read-back technology and thus applies equally well to future recording (writing) technologies such as heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR). [4]

Contents

Overview

The TDMR approach arose from a working group set up under INSIC to explore alternative future storage technologies. [5] [6] In the initial concept, the data-tracks were assumed to be very narrow tracks created by shingled recording and subject to considerable mutual interference. The read-heads were assumed to be each centered over a corresponding data-track and a joint detector would optimally recover data from several tracks simultaneously. [7] [8] The technique was viewed as akin to PRML in providing gains similar to and in addition to the gains from PRML but operating across the tracks rather than down the track. A relatively large body of subsequent work has explored this configuration primarily from the perspective of signal processing. [9] [10] [11] [12] [13] However, the technical challenge of creating an array of closely spaced read-heads and the complexity of jointly detecting data simultaneously on several tracks are both considerable.

Implementations

First implementation of TDMR in a product (2017) TDMR implementation.jpg
First implementation of TDMR in a product (2017)

In 2017, M. Fatih Erden announced at the TMRC conference that Seagate had been shipping HDDs with TDMR since earlier that year. [14] [15] This was followed by Western Digital in 2018 [2] [16] and Toshiba in 2019. [17] [18] These actual first implementations of TDMR are much simpler and very different to the scenario originally envisioned above. Current implementations recover only a single track using a read head with just two read-elements stacked one above the other (i.e. downtrack) and rely on the skew arising from the use of a rotary actuator to create some cross-track separation between the sensors. [19] This TDMR approach is being applied to both Shingled (SMR) and conventional PMR HDDs. [20] The gains achieved are quite modest (6 to 12%) but are expected to increase going forward as more complex schemes are implemented. [21]
In concept, there is little change to the read electronics except that the equalizer that shapes the signal prior to detection now has two inputs and must be appropriately optimized. [22] However, in practice, there is significant added complexity in the read electronics and in the setup process during manufacturing. This complexity is associated with optimization of the equalization (waveform shaping) and timing recovery for the dynamically varying offtrack conditions – further complicated by the cross-track offset between readers that varies with radius. [23] [24]

The HDD servo system also utilizes the position error signals from the two readers. Doing so reduces the repeatable runout, especially when the readers have a wider separation. [25]

Related Research Articles

<span class="mw-page-title-main">Hard disk drive</span> Electro-mechanical data storage device

A hard disk drive (HDD), hard disk, hard drive, or fixed disk, is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with 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 when powered off. Modern HDDs are typically in the form of a small rectangular box.

<span class="mw-page-title-main">Seagate Technology</span> American data storage company

Seagate Technology Holdings plc is an American data storage company. It was incorporated in 1978 as Shugart Technology and commenced business in 1979. Since 2010, the company has been incorporated in Dublin, Ireland, with operational headquarters in Fremont, California, United States.

In computer data storage, partial-response maximum-likelihood (PRML) is a method for recovering the digital data from the weak analog read-back signal picked up by the head of a magnetic disk drive or tape drive. PRML was introduced to recover data more reliably or at a greater areal-density than earlier simpler schemes such as peak-detection. These advances are important because most of the digital data in the world is stored using magnetic storage on hard disk or tape drives.

<span class="mw-page-title-main">Magnetic storage</span> Recording of data on a magnetizable medium

Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.

Density is a measure of the quantity of information bits that can be stored on a given length of track, area of the surface, or in a given volume of a computer storage medium. Generally, higher density is more desirable, for it allows more data to be stored in the same physical space. Density therefore has a direct relationship to storage capacity of a given medium. Density also generally affects the performance within a particular medium, as well as price.

Perpendicular recording, also known as conventional magnetic recording (CMR), is a technology for data recording on magnetic media, particularly 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. The first industry-standard demonstration showing unprecedented advantage of PMR over longitudinal magnetic recording (LMR) at nanoscale dimensions was made in 1998 at IBM Almaden Research Center in collaboration with researchers of Data Storage Systems Center (DSSC) – a National Science Foundation (NSF) Engineering Research Center (ERCs) at Carnegie Mellon University (CMU).

In computing, a hybrid drive is a logical or physical storage device that combines a faster storage medium such as solid-state drive (SSD) with a higher-capacity hard disk drive (HDD). The intent is adding some of the speed of SSDs to the cost-effective storage capacity of traditional HDDs. The purpose of the SSD in a hybrid drive is to act as a cache for the data stored on the HDD, improving the overall performance by keeping copies of the most frequently used data on the faster SSD drive.

Heat-assisted magnetic recording (HAMR) is a magnetic storage technology for greatly increasing the amount of data that can be stored on a magnetic device such as a hard disk drive by temporarily heating the disk material during writing, which makes it much more receptive to magnetic effects and allows writing to much smaller regions.

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Shingled magnetic recording (SMR) is a magnetic storage data recording technology used in hard disk drives (HDDs) to increase storage density and overall per-drive storage capacity. Conventional hard disk drives record data by writing non-overlapping magnetic tracks parallel to each other, while shingled recording writes new tracks that overlap part of the previously written magnetic track, leaving the previous track narrower and allowing higher track density. Thus, the tracks partially overlap similar to roof shingles. This approach was selected because, if the writing head is made too narrow, it cannot provide the very high fields required in the recording layer of the disk.

<span class="mw-page-title-main">Yoshihiro Shiroishi</span>

Yoshihiro Shiroishi was born in 1951 in Tokyo, Japan. He is a Chief Architect and Technical Advisor at the Hitachi Research & Dev. Group, Tokyo, Japan. Shiroishi was named Fellow of the Institute of Electrical and Electronics Engineers (IEEE) in 2015 for leadership in the development of high density magnetic recording technologies and devices.

<span class="mw-page-title-main">Mason Lamar Williams</span> American engineer, physicist, and inventor in Magnetic Recording

Mason Lamar Williams III was an engineer and physicist, noted for his contributions in the areas of magnetic recording and data storage on hard disk drives (HDD). A large part of his career was with the IBM Almaden Research Center in San Jose, California. After retiring, Williams played a major role in the restoration and demonstration of the IBM RAMAC at the Computer History Museum in Mountain View, California

<span class="mw-page-title-main">Robert Fontana</span> American data storage engineer, inventor, and author

Robert E Fontana is an engineer, physicist, and author who is noted for his contributions in the areas of magnetic recording and data storage on hard disk drives (HDD) and on digital tape recorders. His work has concentrated on developing thin film processing techniques for nano-fabrication of magnetic devices including Giant Magnetoresistance read heads now used universally in magnetic recording. Much of his career was with IBM in San Jose, California. He is a Fellow of the Institute of Electrical and Electronics Engineers and a member of the National Academy of Engineering.

<span class="mw-page-title-main">Michael Mallary</span> American data storage engineer, inventor, and author

Michael L. Mallary is an engineer, physicist, inventor, and author who is noted for his contributions in the areas of magnetic recording and data storage on hard disk drives (HDD). His work has concentrated on developing and optimizing magnetic components to maximize data storage density. In particular, he is responsible to inventing the 'trailing-shield' write head used universally in modern HDDs. Mallary is a Fellow of the Institute of Electrical and Electronics Engineers and recipient of the IEEE Magnetics Society Achievement Award.

<span class="mw-page-title-main">Neal Bertram</span> American physicist, teacher, and author

Neal Bertram is a physicist noted for his contributions to the theory of magnetic recording. From 1968 to 1985, he worked for Ampex Corporation in Redwood City. From 1985 to 2004, he was an Endowed Chair Professor at the Center for Memory and Recording Research (CMRR), University of California at San Diego. He is the author of the book "Theory of Magnetic Recording". He is an elected Fellow of the Institute of Electrical and Electronics Engineers. In 2003, he won the IEEE Reynold B. Johnson Information Storage Systems Award.

<span class="mw-page-title-main">David Thompson (engineer)</span> American data storage engineer and inventor

David A. Thompson is an American electrical engineer and inventor with a long career at IBM. He is noted for his many contributions to magnetic recording technology. Thompson was inducted into the National Inventors Hall of Fame for the invention and development of the thin-film inductive head and the magnetoresistive read head. These heads are now ubiquitous in all hard-disk drives and magnetic tape recorders.

Albert Smiley Hoagland had a long career on the development of hard disk drives (HDD) starting with the IBM RAMAC. From 1956 to 1984, he was with IBM in San Jose, California, and then, from 1984 to 2005, he was the director of the Institute for Information Storage Technology at Santa Clara University. He wrote the first book on Digital Magnetic Recording. Hoagland played a central role in the preservation and restoration of the IBM RAMAC now displayed at the Computer History Museum, Mountain View, California. He died in Portland, Oregon, on 1st October 2022.

References

  1. ↑ A. Shilov speaking with Mark Re, Seagate CTO, "The evolution of hdds in the near future", AnandTech: 6 July, 2016
  2. 1 2 T. Coughlin, "Two-dimensional Magnetic Recording and other HDD news", Forbes: Enterprise Tech., Apr 29, 2018
  3. ↑ R. LuTchessi, "Two-Dimensional Magnetic Recording (TDMR)", Silverton Consulting blog, Mar. 5th, 2014
  4. ↑ C. Mellor, "MAMR Mia! Western Digital's 18TB and 20TB microwave-energy hard drives out soon", The Register, Sept 4, 1019
  5. ↑ R. Wood, "Shingled Writing and Two-Dimensional Magnetic Recording", INSIC Annual Meeting, Alternative Storage Technologies 2009: You Want to Build What?, 5 Aug. 2009
  6. ↑ R. Wood, "Shingled Magnetic Recording (SMR) and Two-Dimensional Magnetic Recording (TDMR)", JMMM, Vol. 561, article 169670, Nov. 2022
  7. ↑ R. Wood, M. Williams, A. Kavcic, J. Miles, "The Feasibility of Magnetic Recording at 10 Terabits per Square Inch on Conventional Media", IEEE Trans. Magn., vol. MAG-45, No. 2, pp. 917-923, Feb. 2009
  8. ↑ R. Wood, "Shingled Magnetic Recording and Two-Dimensional Magnetic Recording", presented at IEEE Magnetics Society, Santa Clara Valley Chapter, Oct. 19th, 2010
  9. ↑ Krishnan, Radhakrishnan, Vasic, Kavcic, Ryan and Erden. Two-Dimensional Magnetic Recording: Read Channel Modeling and Detection. IEEE. Trans on Magnetics, 45:3830-3836, 22 Sept., 2009. 2009 (Best Student Paper” award for 2010 by IEEE Data Storage Committee)
  10. ↑ K. Chan, R. Radhakrishnan, K. Eason, M. Elidrissi, J. Miles, B. Vasic, A. Krishnan, "Channel Models and Detectors for Two-Dimensional Magnetic Recording", IEEE Trans. Magn., Vol. 46, No. 3, pp. 804 - 811, Mar. 2010
  11. ↑ A. Kavcic, X. Huang, B. Vasic, W. Ryan, F. Erden, "Channel Modeling and Capacity Bounds for Two-Dimensional Magnetic Recording", IEEE Trans. Magn., Vol. 46, No. 3, pp. 812-818, 17 Feb., 2010
  12. ↑ R. Victora, S. Morgan, K. Momsen, E. Cho, F. Erden, "Two-Dimensional Magnetic Recording at 10Tbits/in2", IEEE Trans. Magn., Vol., 48 No. 5, pp. 1697 - 1703, 19 April 2012
  13. ↑ S. Garani, L. Dolecek, J. Barry ; F. Sala ; B. Vasić, "Signal Processing and Coding Techniques for 2-D Magnetic Recording: An Overview", IEEE Proceedings, Vol. 106, No. 2, pp. 286-318, Feb. 2018
  14. ↑ M. Kief, I. Tagawa, "The 28th Magnetic Recording Conference (TMRC 2017)", IEEE Trans. Magn., Vol. 54, No. 2, Feb. 2018 0200101
  15. ↑ Tom's Hardware: P. Alcorn, "Seagate Announces 14TB Barracuda Pro, IronWolf, and IronWolf Pro", Sept. 10th, 2018
  16. ↑ Western Digital Ultrastar HC530 data sheet
  17. ↑ AnandTech: Toshiba at CES2019: Worlds first 16TB TDMR HDD Debuts
  18. ↑ M. Abe & T. Hara, "Nearline TDMR HDDs with Industry’s Largest Capacity of 16 Tbytes", Toshiba Technology Review, Vol. 74., No. 6, pp. 8-11, Nov. 2019
  19. ↑ J. Coker, "Opportunities and Challenges for Two-Dimensional Magnetic Recording", IEEE Distinguished Lecture, May 7th, 2015
  20. ↑ "Non-shingled and ready to mingle: WDC catches up with 14TB disk rivals", C. Mellor, The Register, 18 Apr, 2018
  21. ↑ S. Dahandeh, F. Erden, R. Wood, "Areal-Density gains and Technology Roadmap for Two-Dimensional Magnetic Recording", TMRC 2015 Digest Book, paper F1, 17-19 Aug., 2015
  22. ↑ R. Wood, R. Galbraith, J. Coker, "Two-Dimensional Magnetic Recording (TDMR): Progress and Evolution", IEEE Trans. Magn., Vol. 51, No. 4, pp. 3100607, April 2015
  23. ↑ M. Oberg and N. Nagare, "Two Dimensional Magnetic Recording System, Devices, and Methods", US Patent 9728221, Aug. 8, 2017
  24. ↑ G. Mathew, S. Dziak ; K. Worrell, J. Singleton, B. Wilson, H. Xia, "2-D Equalization With Location Diversity and Pre-Adaptation to Handle Off-Track Variation in Array-Reader-Based Hard Disk Drives", IEEE Trans. Magn., Vol 54, No. 2, p. 3000307
  25. ↑ G. Guo and J. Yu, "Data storage device comprising dual read sensors and dual servo channels to improve servo demodulation", US Patent 901382, Apr. 21, 2015.
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