Disk Industry on Track for 100G Per Square Inch

SINGAPORE (03/08/2000) - The hard disk drive industry is on track to achieve areal storage densities of 100G bits per square inch (bsi) of disk surface area -- the storage equivalent of the processor developers' 1GHz chip -- within two years, industry executives said here today at the Diskcon Asia-Pacific conference.

"In February last year we got to 10G (bsi) and within a few years commercial products will be out with densities of 100G," Michael Russak, chief technology officer of HMT Technology Corp., said in a speech.

A density of 10G bsi equates to storage capacity of about 14G bytes on a single 3.5-inch platter, according to HMT. Both HMT and IBM Corp. have demonstrated drives with densities of 35G bsi, and when the 100G bsi drives are ready, desktop PCs will be capable of storing at least 150G bytes.

The disk drive industry has gone from a 60 percent annual improvement to an annual doubling of storage capacity in the last few years, executives said.

According to IBM projections, where 15G-byte drives are the standard for a desktop PC today, 100G-byte drives will be the standard some time in 2004.

The 100G bsi target can be reached with evolution of existing technology of horizontal recording and giant magneto-resistive heads, according to Russak.

In horizontal recording, no use is made of a possible third dimension for storage elements, reaching down perpendicularly into the media surface. Experts believe using this third dimension could boost areal storage densities to 500G bsi. But despite these limitations, Russak expects horizontal recording to be around for some time.

"Horizontal recording will not die as quickly as people think," he said. "We expect to see creativity continue here to take horizontal recording up to the 100G (bsi) level."

Several technical aspects of drive and media manufacturing need to be improved to take areal storage densities to that level, according to Russak.

These include flatter and more uniform disk media to enable read or write heads to fly closer to the surface; keeping the signal-to-noise ratio sufficiently high as the recording density increases; and preventing thermal instability, which is the tendency of a magnetic bit to flip states if the medium absorbs some stray thermal energy.

This effect is likely to end advances in horizontal recording somewhere above 100G bsi, as a fundamental physical limit called the superparamagnetic limit is reached.

As recording tracks get closer together, vibration has significant potential to throw the head off the correct track, a tendency which will require more rigid glass-ceramic disk substrates to be developed, Russak said.

As capacities grow, so does the need to improve access and seek performance and I/O data transfer rates. Internal data transfer rates have now reached about 60M bytes per second and are improving at 40 percent per annum, according to IBM figures.

Rotational speeds, now commonly 7,200 revolutions per minute (rpm), will rise to 15,000 rpm next year. Seek times will drop from 8.5 milliseconds in an entry-level server drive to 4 milliseconds by 2004, according to IBM figures.

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