Vertical limit
Vertical limit
May 01, 2005: Stuart Finlayson examines the advances made in the technique of turning data storage on its head that is set to do likewise to the storage industry
The storage technique known as perpendicular recording is by no means a new phenomenon. Indeed, perpendicular recording has its roots as far back as the late 19th century, in the work of Danish scientist Valdemar Poulsen, who is generally considered the first person to magnetically record sound using perpendicular recording.
What is new though is the way in which the technique has been refined by the leading players in the hard drive market, refinements which has turned the potential for creating vastly denser microdrives into a commercial reality.
Perpendicular recording gets its name from the vertical alignment of data bits on the plane of the disk, which uses up less room than the horizontal orientation of today's longitudinal recording technology. To be accurately recorded and read, the more closely-packed perpendicular bits also require a closer association between the read/write head and the recording media.
While the hard drive industry has been using longitudinal recording successfully for five decades, it is now considered to be within two product generations of reaching its practical limit. Researchers are finding that longitudinal recording is losing its ability to maintain data integrity at areal densities much beyond 120GB per square inch. Hence the fact that there is a real sense of urgency among drive manufacturers to get perpendicular drives.
Tight race, tiny space
With the demand for small form drives soaring to unprecedented levels, owing to the popularity of mobile devices which require a lot of storage capacity, such as MP3 players, hard drive vendors are understandably clamouring to get their new, high density perpendicular drives out to the market.
Toshiba was one of the first companies to hit the front in the race for higher capacity and smaller sized storage hard disk drives at the end of last year with the release of its MK8007GAH 80GB two platter hard disk drive. Measuring just 1.8 inches, it is small enough to fit inside many portable devices, such as iPods and PDAs.
The drive, which uses perpendicular recording, offers 206 megabits per square millimetre. Toshiba is planning to roll out the use of perpendicular storage with its future products too, and it plans to eventually include the technology with its 0.85in drives.Hitachi Global Storage Technologies (HGST) soon announced that it too had made new advancements to perpendicular recording that would enable it to create microdrives that will more than double the storage capacity of mobile devices.
HGST has demonstrated data density at 230 gigabits per square inch on perpendicular recording. This feat, which represents a doubling of today's highest longitudinal recording densities, will be implemented in commercial hard drive products in 2007. Current microdrives, such as those featured in the iPod mini, are only available up to 6GB. This breakthrough will facilitate the release of a 20GB iPod mini (HGST supplies drives to Apple for its iPod range), as well as a host of other applications.
HGST achieved the 230GB per square inch density by manipulating the head and media so that the distance between them is a mere 10 nanometers or 1/10,000th of a human hair."We are at the cusp of the most significant hard drive technology transition of the past decade, and it's one that holds so much promise for the hard drive and consumer electronics industries," said Jun Naruse, CEO, HGST. "Demand for storing more data on smaller devices has provided a strong impetus for us to pursue perpendicular recording with a greater sense of urgency."
When fully realised over the next 5-7 years, HGST claims that perpendicular recording could enable a 10-fold increase in data densities over longitudinal recording, paving the way for new heights in capacity such as a 60 GB one-inch drive.
While the transition to perpendicular recording will start as early as the next product generation, Hitachi believes the true potential will be realised in the 200+ GB per square inch range-the point of technology maturation when it claims meaningful advancements in storage capacity will ensure full-scale adoption of perpendicular recording technology. HGST has been conducting field tests with the 230 GB per square inch drives since the end of last year, test which it says have revealed encouraging data about future mass-market adoption of the new technology.
Hard disk drive manufacturer Maxtor's wholly-owned subsidiary, MMC Technology, has also embraced the perpendicular recording medium.
"The storage requirements customers demand are rapidly increasing and we need new recording technologies to maintain hard disk drive area density growth trends," says Craig Davis, national sales manager, Maxtor. "By recording data so that it is perpendicular to the read/write head versus current longitudinal recording, more data can be stored in a platter."
"The formula for perpendicular recording success from a disk point of view depends as much on the cost of production as it does on the recording density capability," stresses Dr Ken Johnson, vice president of research and development at MMC Technology. "We've made achievements in reducing production costs by using existing capital equipment and in improving media performance through technological innovations."
The appliance of science
Professor Shun-ichi Iwasaki, president and chief director of Japan's Tohoku Institute of Technology, is considered to be one of the father of modern perpendicular recording. He is delighted that the method of storage which has been in the pipeline for many years is finally coming to fruition.
"I have been engaged in magnetic recording research since 1951 and found that the most important subject in this field is high-density recording. Around 1975, I began to feel that the vertical direction was the right way to go to attain high-density recording, and began leading the activities to make perpendicular recording a practical technology. I am very glad to see that the technology will come into use soon."
Meanwhile, hard drive industry analyst and historian, Jim Porter believes that the future importance of perpendicular recording cannot be overstated.
"The health of this industry over the next 5-10 years is critically tied to the successful implementation and transition to perpendicular recording technology."
Evolution, not revolution
Not everyone shares HGST's view that its upcoming microdrives represent an industry "breakthrough." Rival vendor Seagate, for one, whose chief technical officer, Dr Mark Kryder insists that HGST is merely following the trend, rather than setting one."We view achieving an areal density of 230 gigabits per square inch in magnetic recording products in 2007 as the natural progression of the technology, not a breakthrough.
"Seagate already has disc drives with over 100 gigabits per square inch areal density in the marketplace (our 400 gigabyte desktop drive using 3 platters at 133 gigabytes per platter, for instance). All other companies are using additional heads and discs in their drives in order to achieve this capacity and consequently have higher costs and poorer reliability."
Dr Kryder points to the precedent set by the industry in the last quarter of a century to back up his assertion.
"The areal density of magnetic recording has advanced 50,000 times since Seagate introduced the first 5.25" drive in 1979, so HGST's suggestion that it will advance a factor of two in the next two years is therefore not a surprise. Seagate is a leader in perpendicular recording technology and has made far more than a thousand perpendicular drives since June, 2003. We are prepared to introduce it, when it is needed; however, we expect to continue introducing higher density longitudinal recording products in the immediate future.
"Perpendicular recording is, however, an important technology. It will enable hard disc drives to continue advancing areal density at a rapid pace and therefore continue enabling new applications, particularly in the consumer electronics area."
What does the future hold?
The point of time where the physical limit of longitudinal recording-known as the superparamagnetic limit, when the magnetic particles on a disk become so minute that they become susceptible to demagnetising forces within the drive-will be reached is on the horizon.
Seagate CTO, Dr Mark Kryder says that longitudinal recording still has time left before reaching the superparamagnetic limit, but warns: "A great challenge is maintaining a strong signal-to-noise ratio for the bits recorded on the media. When the bit size is reduced, the signal-to-noise ratio is decreased, making the bits more difficult to detect, as well as more difficult to keep stable."
Even though perpendicular recording will take magnetic recording technology much further than the current longitudinal methods, superparamagnetic effects still exist at some point, though it is difficult to predict exactly when this will occur.
"At this time, we estimate that perpendicular recording methods may take us all the way to one terabit per square inch," offers Dr Kryder. "When that level is reached, a single 3.5 inch disc will store over one terabyte of information."
While that amount of storage is a significant advance beyond that of storage capacity available in a single drive today, when put into perspective with the best estimates and forecasts of our current and future storage requirements, the need for technologists to continue to forge ahead beyond that figure is clear.
A recent study by the University of California Berkeley reported that the world produces between 1 and 2 exabytes (one exabyte is the equivalent of one billion gigabytes) of information each year in total, comprising all magnetic, paper, film, and optical data. In addition to that sum, it is conceivable that eventually much of the older media such as those produced on film and paper may also make its way to magnetic data translation, increasing the overall total figure further.
So where will the industry go when the physical limit of perpendicular recording does arrive? Will a superior recording technique supersede it?
The good news is that technologists are already beginning to explore other possible methods of recording data beyond longitudinal and perpendicular recording.
Though still many years away, Heat Assisted Magnetic Recording (HAMR) is viewed as a possible candidate for storing the world's information.
HAMR involves producing a hot spot (commonly with a laser) on the media, while data is simultaneously written magnetically. The net effect is that when the media is heated, the coercivity-or field required to write on the media-is reduced, making it possible to write high-coercivity media (which have higher stability against superparagmagnetism), in spite of the limited fields that can be produced by recording heads.
"Perpendicular recording is expected to enable recording of a few hundred gigabits per square inch, but we expect other technologies such as Heat Assisted Magnetic Recording to be required to carry us beyond 1 terabit per square inch," says Dr Kryder.
Fellow Seagate technologist Dr Dieter Weller is working on another method known as patterned media, or self-ordered magnetic arrays (SOMA). "A typical bit of information is made up of about 100 grains of material. We are working to convert each grain to a unique bit of information. As a result, a large gain in bit density would be achieved," explains Dr Weller.
Seagate Research is also working on ways to make the grains "order" in a regular array so that the bits can be read and written, so that good thermal stability can be achieved.With the amount of data stored in the last two years amounting to more than the entire amount of information recorded in the history of mankind, and the need for more and more storage capacity showing no signs of waning, it will no doubt be reassuring to enterprises that technologists continue to find new and innovative ways to meet the extraordinary demand.
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