Conventional drives can reach a terabyte

Conventional magnetic disk drives can overcome previously forecasted limits and ultimately achieve storage densities of one terabyte (1,000G bytes) per square inch, according to Ed Grochowski, program manager for advanced disk storage products at IBM Corp. Standard drives today store around 20G bytes per square inch.

Earlier estimates suggested that magnetic storage densities would be limited to around 40G bytes per square inch by the superparamagnetic effect, a fundamental constraint caused by the thermal instability of magnetization of tiny elements of the surface of the disk media.

According to Grochowski, this view is overly pessimistic, as several new technologies are pointing the way towards continuing the industry's recent record of doubling storage densities each year.

Among the most promising advances -- and one of the first which will be commercially introduced -- is antiferromagnetic coupled (AFC) media for use as a disk media surface. By layering a ferromagnetic film over an antiferromagnetic film, separated by a ruthenium- based exchange film, key parameters such as the measure of remanence thickness (Mrt) can be considerably improved. This enables more bits to be stored stably in a given area, improving storage capacity, according to Grochowski.

"This technology will be the first one used to delay the onset of superparamagnetism and I expect to see it in products very soon," he said during a presentation at Diskcon Asia here Wednesday. "The prospect of going beyond 200G bytes per square inch appear very good."

Another key technology in future will be perpendicular recording, according to Grochowski. In perpendicular recording, the magnetic poles used in storing data bits are aligned perpendicular to the disk surface, enabling more bits to be stored as adjacent bits interfere less with each other's magnetization.

To improve writing bits to the disk, future systems will use thermal-assisted writing, where a laser pulse heats the spot on the disk where the data bit is about to be written. This lowers the current and magnetic field required to write a data bit, again meaning that bits can be safely stored closer to one another.

In future, disk media will be patterned, rather than being a homogeneous surface, according to Grochowski. A bit pattern will be etched by lithography or ion beam exposure, and the bits will be effectively isolated from magnetic fields applied to their neighbors. The ultimate structure will be where one grain of magnetic alloy stores one bit of data, Grochowski said.

"There is a long regime ahead of enhanced magnetic disk drives, with AFC as the first technology," he said. "We should be good for 10 years going forward, maybe more. One terabyte (per square inch) is a definite possibility with these technologies."

Diskcon continues through Thursday.

More information about the conference can be found at http://www.idema.org.

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