ZPi | Lord Kelvin And Your Hard Drive
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Lyle Zapato

Lord Kelvin And Your Hard Drive

Lyle Zapato | 2005-02-27.2800 LMT | Kelviniana | Technology

Kelvin's "On the Electro-dynamic Qualities of Metals" describes his experiments with bits of nickel and iron that showed their electrical resistance changed depending on how they were oriented in a magnetic field.

What's so interesting about this 148 year old experiment? It marks the discovery of a phenomenon today known as anisotropic magnetoresistance (AMR) which is used by modern hard drives to read data. Just like in Kelvin's experiments, a hard drive's magnetoresistance (MR) read head changes its electrical resistance in response to magnetic fields, thus allowing the drive to read data from changes in the current being sent through the head as the head passes over the spinning magnetic platters.

The introduction of the MR read head (made of an alloy of nickel and iron -- the metals used in Kelvin's experiments,) allowed the explosion in hard drive sizes in the late '90s as they replaced the older, less-sensitive inductive read/write heads. (The original MR heads are now being replaced by even-more-sensitive giant magnetoresistive heads, which still contain an AMR element.)

So, the next time you look through your multi-gibioctet collection of MP3s, digicam snaps, and pirated episodes of American television shows, remember to thank the Lord Kelvin for giving you the ability to have greater areal density through the electro-dynamic wonder of anisotropic magnetoresistance.

End of post.