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Last Updated: Thursday, 22 April, 2004, 09:58 GMT 10:58 UK
Hard drive speed limit is reached
Hard drive close-up, Eyewire
The upper limit for writing data has been found
US scientists have found the theoretical maximum speed that data can be written to a PC's hard drive.

They discovered the limit by shooting electrons travelling close to the speed of light at a chunk of the same material used in computer hard drives

This created magnetic field pulses too short to alter the material's properties and record a bit of data.

The discovery might force hard drive makers to use exotic materials or new methods to breach this speed limit.

Quick response

Typically data is written on the platters of hard drives using opposing magnetisations to represent the 0s and 1s of binary information.

Bits are flipped by applying a short-lived magnetic field to reverse the magnetisation at a particular location and turn a 0 into a 1 or vice versa.

In a paper in the journal Nature, Ioan Tudosa and colleagues at Stanford University report that they have found just how short-lived that magnetic pulse can be.

Using the linear accelerator at Stanford University in California, the researchers managed to generate magnetic field pulses in hard drive materials that lasted a mere 2.3 picoseconds.

One picosecond is a millionth of a millionth of a second.

The team discovered that the changes the magnetic pulses made to the material were not reliable enough to use as a way to write data on a hard drive.

The bad news is that this upper limit means that the fastest data can be written using changes in magnetisations is 435,000 million bits every second.

The good news is that this is still one thousand times faster than the best magnetic hard drives in use today.

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