Maxtor technique pushes hard drive capacity

MMC Technology, a subsidiary of hard drive maker Maxtor, claims to have found an economical way to transition to perpendicular recording--a disk technology that promises to keep hard drive capacity growing steadily as current recording technology runs out of steam.

Perpendicular recording is not a new concept, and it's not unique to Maxtor. But the announcement is significant because the company claims it can incorporate the new technology without retooling its manufacturing process or raising costs significantly. Maxtor is not yet disclosing plans to produce disks with the new technology, but executives at MMC say it could occur by the end of 2004.

Initial capacities could reach 175GB per hard drive platter--up from 80GB per platter today, says MMC vice president of research and development Ken Johnson. (Competitor Seagate recently announced 100GB platters.) Maxtor is currently the capacity leader in desktop-style (ATA) hard drives--using four platters to produce a 300GB drive. With 175GB platters, 700GB drives would be possible.

Tipping Magnetics

Perpendicular recording is based on a simple proposition: You can pack more magnetic changes onto a hard drive if you can stack a few of them as well as using the traditional method of squeezing them closer together on the disk's surface.

Today's hard drives use a method called longitudinal recording. The magnetic changes are spread out in rings parallel to the surface of the hard drive platter. The drive's read-write head--essentially a miniature horseshoe magnet--is held over the spinning disc surface and writes magnetic changes that are coded to represent the binary data being stored.

Longitudinal recording is reaching a density limit because the magnetic changes cannot be packed so closely together that they change each other's orientation. They are laid across the disk in a way that maximizes the surface area each can take up, and space is running out. Also, the hard drive coating requires a fair amount of nonmagnetic material to separate the grains and keep them from exerting magnetic forces upon each other. MMC's Johnson likens the bits to tiny bar magnets, saying they "like to be standing vertically next to each other and not opposed to each other."

In perpendicular recording, the magnetic changes are also arranged vertically. Data is encoded by pointing either the magnetic north end or the magnetic negative end of the grain upwards. The read-write head design is also quite different. Instead of a horseshoe shape with positive and negative poles, the single-pole head resembles a needle that writes a magnetic field into the magnetic material and through the disk platter itself to complete a circuit.

Thin, Soft Data Layer

The key to perpendicular recording is a so-called soft layer under the magnetic grains that can easily transmit an electrical current to complete the circuit. In contrast, the magnetic material itself is characterized as "hard" because it is resistant to changing its orientation. This resistance is what ensures that a hard drive can reliably retain the data written to it.

According to Maxtor, laying down a soft magnetic underlayer cost-effectively was the main challenge in creating perpendicular recording platters. Johnson says original estimates found the soft layer alone would have to be up to 400 nanometers thick--dwarfing the 30 to 40 nanometer thickness of all materials required to coat today's hard drive platters. Maxtor says it has been able to get the soft layer down to 100 nanometers.

While that's still a considerable increase in overall thickness for the drive coating, it's thin enough that Maxtor can produce the platters with its current machinery and production methods. "I think we've made a state-of-the-art [perpendicular recording] disk, and we've made it on current equipment," Johnson says.

While perpendicular recording will probably be the ultimate future of hard drive technology, it may or may not appear in the next one or two generations of hard drives. Johnson says Maxtor is also trying to achieve 160GB platters using longitudinal recording.

Industry analysts predict, however, that disks with perpendicular recording are coming soon, and that perpendicular recording will be the dominant hard drive technology by 2006.

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