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Boffins discover upper limit of HD write speed

Magnetic pulse ceiling

By Lucy Sherriff, 22 Apr 2004

Boffins at Stanford had interesting news for storage companies this week, as they announced the discovery of the upper speed limit at which data can be written to a hard drive.

The short term impact should be negligible, however. Companies are unlikely to reach the limit any time soon as it is at around 1000 times the current write-speeds, and requires a linear accelerator. (At 3.2km long, this won’t easily fit in a desktop, and could have serious implications for power consumption.)

Nonetheless, the team at Stanford was looking into the physics of magnetic data storage, and in the time-honoured tradition of lab rats everywhere, they just had to find out how fast they could get it to go.

Writing data to disk involves magnetising teeny bits of the surface with an electromagnetic pulse; the spin of the magnetisation represents the 0 or 1. Faster write-speeds need a strong field to be applied for a really short period. At which point, the linear accelerator really comes into its own.

The team fired electrons down Stanford University’s 3.2km linear accelerator, generating a staccato string of very short magnetic field pulses aimed at a magnetic target. At 2.3 pico seconds, each pulse is noticeably shorter than blink-and-you’ll-miss-it fast, and the field strength of 10 Tesla is around 200,000 times that of the Earth’s own magnetic field.

What the team discovered is that if you pulse too fast, you’ll end up with random magnetic changes, and gobbledegook stored on your hard drive.

Why this should happen is something of a mystery. Team leader Joachim Stör suggests that there may be some kind of thermal disruption at such high frequencies.

The results of the experiment are published in Wednesday’s edition of Nature. ®

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