The incredible shrinking storage media

Last month, IBM Corp. made the stunning announcement that it had written data to a storage medium at a density of 1T bit per square inch, enough to pack 25 million printed pages on a postage-stamp-size chip.

Pundits predicting the progress of IT invariably invoke Moore's Law, by which the density of transistors on a chip and hence the performance of memory and processors has doubled every 18 months for the past three decades.

But that same kind of progress is occurring in other quarters of IT as well. During the 1990s, the storage density of magnetic disks increased 75 percent per year, outpacing even Moore's Law. As for tape, in May, IBM announced that it has developed a linear digital tape cartridge that can hold 1TB of data, 10 times the going rate. IBM says it hopes to drive the cost of tape storage from US$5 per gigabyte (including storage hardware and software) today to 5 cents in five years.

Indeed, advances in magnetic media, and in the drives that write on and read them, promise to keep pushing users happily down those cost curves. And a few new technologies may take storage costs to levels of affordability that fundamentally alter the way companies think about data storage.

Making magnetic media hold more data has traditionally been a matter of making the grains in the recording medium, and the spots that hold the recorded bit, ever smaller and closer together. At the same time, tape and disk heads have become more precise, applying a sharper and better-positioned recording pulse. These improvements have been augmented by better error-correction and control software.

But at about 100G bits per square inch, the magnetic grains begin to interfere with one another, leading to thermal instability and short-lived recordings. So researchers are turning to the following radical new approaches:

IBM's Millipede. The 1T-bit-per-square-inch recording device is reminiscent of the old card-punch. The device uses nanoscale points to punch indentations in a plastic film, one per bit. Unlike a punched card, the film can be rerecorded.

The device could address individual atoms and eventually record between 1 and 10 petabits per square inch, "the ultimate limit," says Currie Munce, director of storage systems technology at Yorktown Heights, N.Y.-based IBM Research. In about four years, Millipede storage will find initial application in mobile devices, where small size and low power requirements are important, he says.

But tiny, power-efficient Millipede devices could go into data centers. For years, the economic yardstick for storage has been dollars per megabyte, Munce says. But companies' appetite for storage is growing so fast that IT managers are starting to evaluate storage media in terms of megabyte per square foot or per watt. "They're saying, 'How much floor space does it take, and how much air conditioning will I require?' " Munce says.

Carnegie Mellon University's HAMR. The Pittsburgh university's Data Storage Systems Center is developing heat-assisted magnetic recording (HAMR) technology that in five years will lead to disk drives with storage densities of 1T bit per square inch. And the goal is to do that with greater reliability than is possible today, says Robert M. White, director of the center.

An HAMR disk drive will look like a conventional drive but will include a laser generator on the read/write head. It solves the thermal stability problem by heating the disk surface with a laser beam at the precise spot where a data bit is to be recorded. That makes it easier to write on the medium, and the subsequent cooling stabilizes the data.

HAMR could take the cost of disk storage, now at about $1 per gigabyte, to 10 cents in five years, White says.

Hewlett-Packard Co.'s Atomic Resolution Storage (ARS). HP is using atomic-scale probes to send beams of electrons to the recording medium, which moves under thousands of these read/write probes. The beams change the medium to either a crystalline or an amorphous state, the state indicating whether a bit has the value 0 or 1. HP says there will be commercial applications within five years.

According to Chuck Morehouse, director of HP's Information Storage Laboratory in Palo Alto, Calif., data access times for ARS devices will be from 10 to 100 times shorter than for conventional hard drives. And the bandwidth for data transfer can be just about anything an application requires, because multiple probes can be deployed in parallel on one chip. "With one ARS device, you'll have the equivalent of read/write heads from many hundreds of disks," Morehouse says.

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