Tuesday, May 22, 2007

A New Kind of Hard Drive

Inside your computer, data is stored on your hard drive in magnetized form. In magneto-speak, an area magnetized in one direction is called a domain. A domain magnetized to the left becomes a “one” and a domain magnetized to the right becomes a “zero.” The disk must spin while it is read, which makes this mechanical system relatively slow.

Once the data is stored electronically, as in integrated circuits, it moves much faster. We can't use electronic systems all the time, though, because the data disappears when you turn the machine off.

IBM’s Stuart Parkin patented the concept of a “racetrack” hard drive in 2004. Imagine a string of red and blue beads. The beads are pushed past a sensor. Rather than looking at whether the bead is red or blue, the sensor looks for the points where the bead color changes.

    Beads and Domains
    In reality, the system is a magnetic wire with many domains. In between the domains is a domain wall, a region in which the atoms switch alignment. It’s like a purple bead in between red and blue groups. A spin-polarized current, or a current in which the spins of the electrons all point in the same direction, causes the domain walls to shift along the magnetic wire. The sensor measures bits as short time slices. If the sensor sees a domain wall in that time, then the bit is a one. If it does not, it’s a zero.

    However it’s not quite like beads on a string. For one, the current does not push the domain wall like a hand pushes a bead. Instead, it’s more like a chain reaction in which the spin-polarized electrons start turning the atoms, which turn their neighbors, and so on. The domains and domain walls move even though the atoms stay in place.

So, if this system was patented in 2004, why am I blogging about it in 2007? Well, this racetrack hard drive was only a concept then. Researchers from Germany, South Korea, and California have been collaborating on a project which could help make it a reality. In early May, they published results in Physical Review Letters with the intimidating title, "Direct Imaging of Stochastic Domain-Wall Motion Driven by Nanosecond Current Pulses."

Unfortunately, the domain walls tend to get snagged on imperfections in the wire. Going back to the beads, it's like a knot in the string. Racetrack hard drives have a way to go before you’ll find them at Best Buy, but they may well be on the distant horizon.

Original story from Physical Review Focus.

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