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HDD makers explore ways to up areal density

Posted: 27 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:HDD makers? HDD areal density? perpendicular recording tech?

Researchers are exploring a new technique to extend the life of perpendicular recording in HDDs. The so-called disk track media is a still-controversial approach that might be able to nearly double the density of bits on a disk.

Currently, drives depend on placing a read/write head over a certain spot on a disk to find a particular piece of data. The new technique defines data locations by patterning continuous tracks on to a bare disk before it is integrated into a drive. The tracks are defined by placing on the media layers of materials with different magnetic characteristics.

"It's probably not a factor of two better than today's approach, but just how much better it is is still being debated, said John Best, chief technologist with Hitachi Global Storage Technologies. "The whole method is still controversial even within our company."

It's not yet clear whether the technique would be significantly less expensive than a separate method that defines a unique space on a blank disk for each data bit. That approach, called bit patterned media, is seen as a next major leap in magnetic recording technology but could take five years to bring to market.

Faster route
For its part, discrete track recording might be available for commercial drives in as little as two years. "The basic concept has been around since the 1980s, but it's been getting a lot of interest just in the last year or two," said Best.

The new technique is one of many research efforts giving engineers hope that perpendicular recording may last longer than previously thought. A year ago researchers from several drive makers said perpendicular recording, introduced in the last year, would take drive makers to areal densities of up to 500Gbits per square inch and support products through 2010.

Today's best drives using perpendicular recording pack about 200Gbits into every square inch of a disk. Some lab demos have shown advances getting to 300Gbits/square inch. "That gives us confidence we can reach the initial goal of 500Gbits," said Best. "Today I think there's a reasonable chance we will get to a Tbit per square inch with perpendicular techniques. That's just my gut feeling. We have not done a thorough technical analysis," said Best.

That could make the technology viable in new disk products through 2012, he added.

Overall, the drive industry is aiming to increase areal density by 40 percent a year, a significant boost though far below the level of nearly 100 percent a year the industry achieved in the 1990s.

Pursuit of longer life
Researchers are also pursuing other methods to extend the life of perpendicular recording including advances in media, heads and read channels, Best said.

Media makers are exploring use of different kinds of magnetic materials in multilayer disks to optimize SNR. Head makers are moving from tunnelling magneto-resistive heads used widely today to giant magneto-resistive heads used in a perpendicular in-plane arrangement. Meanwhile, read channels are being enhanced to detect data under higher bit-error rates.

"Most of these extensions are in getting better aerial density and SNR in media while keeping stability at room temperature," said Best. "It requires a fair amount of invention at every step of the way," he added.

- Rick Merritt
EE Times

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