Computer’s revolution

Scientists Discover Missing Element in Electronic Circuitry
Wired Magazine
2008-05-02

Researchers at HP Labs have built the first working prototypes of an
important new electronic component that may lead to instant-on PCs as well
as analog computers that process information the way the human brain does.
The new component is called a memristor, or memory resistor. Up until today,
the circuit element had only been described in a series of mathematical
equations written by Leon Chua, who in 1971 was an engineering student
studying non-linear circuits. Chua knew the circuit element should exist —
he even accurately outlined its properties and how it would work.
Unfortunately, neither he nor the rest of the engineering community could
come up with a physical manifestation that matched his mathematical
expression.
Thirty-seven years later, a group of scientists from HP Labs has finally
built real working memristors, thus adding a fourth basic circuit element to
electrical circuit theory, one that will join the three better-known ones:
the capacitor, resistor and the inductor.
Researchers believe the discovery will pave the way for instant-on PCs, more
energy-efficient computers, and new analog computers that can process and
associate information in a manner similar to that of the human brain.
According to R. Stanley Williams, one of four researchers at HP Labs’
Information and Quantum Systems Lab who made the discovery, the most
interesting characteristic of a memristor device is that it remembers the
amount of charge that flows through it.
Indeed, Chua’s original idea was that the resistance of a memristor would
depend upon how much charge has gone through the device. In other words, you
can flow the charge in one direction and the resistance will increase. If
you push the charge in the opposite direction it will decrease. Put simply,
the resistance of the devices at any point in time is a function of history
of the device — or how much charge went through it either forwards or
backwards. That simple idea, now that it has been proven, will have profound
effect on computing and computer science.
“Part of what’s going to come out of this is something none of us can
imagine yet,” says Williams. “But what we can imagine in and of itself is
actually pretty cool.”
For one thing, Williams says these memristors can be used as either digital
switches or to build a new breed of analog devices.
For the former, Williams says scientists can now think about fabricating a
new type of non-volatile random access memory (RAM) – or memory chips that
don’t forget what power state they were in when a computer is shut off.
That’s the big problem with DRAM today, he says. “When you turn the power
off on your PC, the DRAM forgets what was there. So the next time you turn
the power on you’ve got to sit there and wait while all of this stuff that
you need to run your computer is loaded into the DRAM from the hard disk.”
With non-volatile RAM, that process would be instantaneous and your PC would
be in the same state as when you turned it off.
Scientists also envision building other types of circuits in which the
memristor would be used as an analog device.
Indeed, Leon himself noted the similarity between his own predictions of the
properties for a memristor and what was then known about synapses in the
brain. One of his suggestions was that you could perhaps do some type of
neuronal computing using memristors. HP Labs thinks that’s actually a very
good idea.
“Building an analog computer in which you don’t use 1s and 0s and instead
use essentially all shades of gray in between is one of the things we’re
already working on,” says Williams. These computers could do the types of
things that digital computers aren’t very good at — like making decisions,
determining that one thing is larger than another, or even learning.
While a lot of researchers are currently trying to write a computer code
that simulates brain function on a standard machine, they have to use huge
machines with enormous processing power to simulate only tiny portions of
the brain.
Williams and his team say they can now take a different approach: “Instead
of writing a computer program to simulate a brain or simulate some brain
function, we’re actually looking to build some hardware based upon
memristors that emulates brain-like functions,” says Williams.
Such hardware could be used to improve things like facial recognition
technology, and enable an appliance to essentially learn from experience, he
says. In principle, this should also be thousands or millions of times more
efficient than running a program on a digital computer.
The results of HP Labs teams findings will be published in a paper in
today’s edition of Nature. As far as when we might see memristors actually
being used in actual commercial devices, Williams says the limitations are
more business oriented than technological.
Ultimately, the problem is going to be related to the time and effort
involved in designing a memristor circuit, he says. “The money invested in
circuit design is actually much larger than building fabs. In fact, you can
use any fab to make these things right now, but somebody also has to design
the circuits and there’s currently no memristor model. The key is going to
be getting the necessary tools out into the community and finding a niche
application for memristors. How long this will take is more of a business
decision than a technological one.”

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