Going beyond perpendicular

Future hard disk drive technologies will continue the march to increased capacity


Techworld interviewed John Best, the chief technology officer for Hitachi GST. It’s the fiftieth birth day of the invention of the hard drive and we wanted to discuss what happens next.

TWJohn, could you just summarise the first half century of hard drive capacity development, and give us your picture of the next few years please?

John BestOver the last 50 years, the industry has experienced a phenomenal pace of technological advances that has led to a 70-million-fold increase in areal density, the measurement of how much data can be placed on a disk.

Now, as we look forward to the next 50 years, the future looks bright for the longevity of the hard disk drive. With the advent of portable consumer devices that use hard drives, the industry is challenged, more than ever, to keep the pace of increasing capacities and decreasing form factor (size). Today, companies like Hitachi are engaged in research into advanced technologies that will extend the capabilities of the hard drive, and allow the industry to continue to double capacity every two years, enabling the exponential growth in consumer devices, particularly video applications, which utilise hard drives.

TWPerpendicular recording has just arrived. Could you review why it came along?

John BestPerpendicular magnetic recording (PMR), began shipping in volume this year. PMR technology addresses one of the key challenges facing the hard drive industry: overcoming the constraints imposed by the super-paramagnetic effect. Each bit of data on the disk is stored in the magnetic direction of a hundred or so microscopic magnetic grains. To shrink the bits, and increase the density of storage, the individual magnetic grains are made smaller. The super-paramagnetic effect occurs when the microscopic magnetic grains on the disk become so tiny that they lose their ability to hold their magnetic orientations at room temperature. The result is that data on the disk is spontaneously erased, corrupting data and rendering it and the storage device unreliable and thus unusable.

Perpendicular recording aligns the magnetic direction of the bits vertically, perpendicular to the disk. In contrast, its predecessor, longitudinal recording, as its name indicates, aligns the magnetic direction of data bits horizontally, parallel to the surface of the disk. With a perpendicular orientation, the magnetic field used to write the information on the disk can be made much stronger. This allows the magnetic material storing the bits to be made with a material that is much more resistant to changing its magnetic direction, and to be thicker. Because of these changes, with perpendicular recording, the spontaneous data erasure of the super-paramagnetic effect does not occur until the bits are made much smaller than with conventional, longitudinal, magnetic recording.

Hitachi expects that with the advancements in areal density that come from PMR technology, it will able to produce, by decade end, a two-terabyte (TB) 3.5-inch desktop drive or a 400-gigabyte (GB) 2.5-inch notebook drive.

TWWhat happens after that? Are there other technologies on your technology radar screen?

John BestHitachi researchers are studying extensions to PMR technology, such as patterned media and thermally-assisted recording, which will allow for a consistent pace of areal density improvements well into the next decade.

Today, roughly 100 magnetic grains make up a single bit of data. With patterned media, researchers are creating isolated magnetic islands with one magnetic grain representing a bit of data. With fewer magnetic grains, patterned media allows more bits of data per square inch of disk space without suffering from the limits of the super-paramagnetic effect.

With thermally-assisted recording, magnetic grains can be smaller while still resisting thermal fluctuations at room temperature. As the name suggests, thermally-assisted recording uses a laser to heat up the media while the magnetic head is writing the smaller bits of data. This enables the use of media that is magnetically stable at room temperature with the very small magnetic grains required for high-density storage.

TWWhen might these technologies arrive in products?

John BestHitachi predicts that patterned media technology could ship in products as early in the next decade. Several years beyond that, the company believes patterned media and thermally-assisted recording could be combined and delivered at the time when patterned media alone is insufficient to sustain areal density progress.

TWDo you think the general future for hard drives is bright?

John BestThe march for improvements in areal density continues unabated as the hard disk drive industry looks to develop products that address the explosion in digital content; content that needs to be stored, searched, retrieved and shared. Technologies like perpendicular magnetic recording, patterned media and thermally-assisted recording will ensure that the industry can keep pace with the ever increasing hunger for storage capacity.

I’ll give you an example of what this means: the industry is poised to ship more hard drives in the next five years than it has in the last 50.

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