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What's New in Storage Technology

A disk is a disk is a disk, right? Well, not necessarily. By Lynn Greiner
When you're thinking about mass storage, a disk is a disk is a disk, right?

Well, not necessarily.

While we users been happily using up space, and trying to figure out how to cram more disk drives into our already crowded infrastructures, drive manufacturers have been working equally hard on technologies that generate more storage per platter. And while we've been worrying about transfer speeds and reliability, they've been creating new interfaces and trying other tricks to pour the bits through the wire more quickly.

A brief refresher on how the drives work may be in order here. A disk drive is composed of one or more platters - aluminum or glass and ceramic disks, with a magnetic coating - that spin rapidly beneath hovering read-write heads that actually float above the platter on a thin film of air. Data on a disk is stored in binary code - zeros and ones - represented by the magnetic state of individual bits (short for "binary digits," as you may remember). So the number ten, for example, is represented in binary by 1010 (for a binary primer, check this Wikipedia entry).

As disk platter spins beneath the heads, they read the magnetic state of each bit. "Writing" is simply altering that magnetic state to represent the binary form of the data to be stored.

The trouble is, we're pushing the limits of current drive technology. It's a matter of physics.


Today's mainstream drive technology is known as longitudinal recording. The bits lie flat, like sunbathers on the beach, and their magnetic state determines whether they lie parallel to the direction of head movement or not. As we try to stuff more data onto a platter, the bits (the magnetized particles, which become smaller and smaller as densities get higher) snuggle closer and closer together, until, like those sunbathers, they begin to interfere with each other. On the beach, that can mean an elbow in the ribs or a spilled drink; on a disk, it means unexpected changes of magnetic state, and lost or corrupted data.

The phenomenon is known as the superparamagnetic effect. When particles shrink beyond a certain size, the energy required to change their magnetic state becomes so small that even the heat of the drive's normal operation is enough to trigger it. The effect kicks in at densities of 100-200 gigabits per square inch.

All is not lost, however. If you make those sunbathers stand up, suddenly there's room for a whole lot more of them without crowding (we can disregard the consequences for their tans). Similarly, if bits are vertical instead of horizontal, many more can live in the same space without problems - up to ten times as many. And they can be reliably recorded and read despite the close quarters thanks to their standing on a "beach" that's made of a material that effectively amplifies the signals the heads emit. That's called perpendicular recording, and vendors are just starting to release drives using the technology.

With perpendicular recording, an iPod that now carries 3,000 tunes could support 30,000, assuming you had the time and resources to load them all!

It's admittedly hard to imagine how all this works, so disk manufacturer Hitachi Global Storage Technologies has put together a little animated ditty that explains it all. Check out Get Perpendicular.

Hitachi has also been playing with its chemistry set to figure out the best way to build a read/write head that can cope with the smaller, denser bits. It has put together another animation that explains how its combination of ingredients makes heads that remain stable and reliable under all sorts of environmental fluctuations. Check out this link for a playful take on the subject.

When perpendicular recording hits the wall - estimated at about one terabit per square inch (which means something the size of a floppy disk would be able to store a terabyte of data - the equivalent of a stack of text documents sixteen times the height of the Empire State Building), other technologies will be standing in the wings. Two of many currently under development are optically-assisted storage and self-ordered magnetic arrays (SOMA).

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Related Keywords:storage, trends, physics, perpendicular recording, SATA, SOMA, optical, iscsi, serial attached scsi, hardware

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