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Skating on Entropy: Future Computers

Tomorrow's computers may utilize nano-magnetic processors and memory that allow them to butt heads with the second law of thermodynamics.
By Gabe Kahn.
First Publish: 7/7/2011, 9:46 PM / Last Update: 7/8/2011, 5:15 AM

Future computers may rely on magnetic microprocessors that consume the least amount of energy allowed by the laws of physics, Science Daily reports.

It's not science fiction - it's your tomorrow.

Or so says a team of electrical engineers at UC Berkely whose results were published in the Journal of Physical Review Letters earlier this year.

Today's silicon-based microprocessor chips utlilize electric currents – moving electrons – which generate significant waste heat that must be dissipated. But microprocessors employing nanometer-sized bar magnets -- like itsy-bitsy refrigerator magnets -- for memory, logic and switching operations would theoretically require no moving electrons.

Such chips would dissipate only 18 millielectron volts of energy per operation at room temperature, the minimum allowed by the second law of thermodynamics, which is also called the Landauer limit. In English: that's 1 million times less energy per operation than consumed by contemporary computers!

"Today, computers run on electricity; by moving electrons around a circuit, you can process information," explained UC Berkley graduate student Brian Lambson. "A magnetic computer, on the other hand, doesn't involve any moving electrons. You store and process information using magnets, and if you make these magnets really small, you can basically pack them very close together so that they interact with one another."

Lambson is working with UC Berkeley professor Jeffrey Bokor of electrical engineering and computer sciences, to develop magnetic computers.

"In principle, one could, I think, build real circuits that would operate right at the Landauer limit," said Bokor, who is also a codirector for the Center for Energy Efficient Electronics Science. One of the center's goals is to build computers that operate at the Landauer limit,” Bokor said, noting going lower would be impossible due to entropic effects.

"Even if we could get within one order of magnitude, a factor of 10, of the Landauer limit, it would represent a huge reduction in energy consumption for electronics,” Bokor said. “It would be absolutely revolutionary!"

Back to the Future
Much like now-obsolete floppy disks, Bokor and Lambson are talking about magnetic storage -- but on a radically diminished scale and increased level of sophistication.

The nanomagnets that Bokor's lab use to build magnetic memory and logic devices are about 100 nanometers wide and about 200 nanometers long – only 20% the size of most household germs! But their north-south polarity – like a bar magnet – can be used to represent the 0 and 1 of contemporary binary computer memory.

What's more, when multiple nanomagnets are brought together, their north and south poles interact via dipole-dipole forces -- increased margnetic attraction between the magnets -- to exhibit transistor behavior, allowing simple logic operations.

"The magnets themselves are the built-in memory," Lambson said. "The real challenge is getting the wires and transistors working."

Lambson has proven through calculations and computer simulations that the simple memory operation "restore to one" -- erasing a magnetic bit -- can be conducted at an energy dissipation rate very close, if not identical to, the Landauer limit.

Because the Landauer limit is proportional to temperature, circuits cooled to low temperatures would be even more efficient.

At the moment, electrical currents are used to generate a magnetic field to erase or flip the polarity of nanomagnets, which dissipates a lot of energy. Ideally, new materials will make electrical currents unnecessary.

"The magnetic technology we are working on looks very interesting for ultra low power uses," Bokor said. "We are trying to figure out how to make it more competitive in speed, performance and reliability."

"But we have to figure out a way to put that energy in without using an electricity dependent magnetic field, which is very hard to do efficiently," Bokor explained.

Bokor's research is being underwritten by the National Science Foundation and the Defense Advanced Research Projects Agency.