Tech

BEACH holiday a washout? Camping trip cut short by gales? Cheer up - every storm cloud really does have a silver lining. It seems that the unpredictable behaviour of our weather could hold the key to the future of computing.

If you don't believe it, talk to William Ditto, a physicist at the University of Florida in Gainesville. Along with a team of colleagues in India and the US, Ditto has spent more than 10 years conjuring up the electronic equivalent of chaotic weather systems and harnessing them to build the next generation of computer processors.

In the precisely designed world of computer chips, this is an unconventional approach: any chaotic behaviour is usually seen as a Bad Thing. After all, there's little point building a chip if its carefully regulated signals decay into anarchy as soon as it is switched on. However, Ditto and his colleagues believe that such anarchy can yield huge rewards, if used in the right way.

To prove it, they have harnessed chaotic oscillations to create "chameleon" logic circuits that can switch their behaviour on the fly. In the space of a nanosecond or two, these morphing circuits can transform themselves from a processor unit, say, into a graphics controller. A "chaotic" computer built from circuits like these would be able to make far better use of its precious hardware than today's machines. By throwing all its computational firepower at the task in hand, and then reassigning it the instant a different task comes along, chaotic processor chips would be hugely more powerful than conventional chips of the same size. They would even be able to repair themselves.

Ditto has founded a company to commercialise the technology, but in the meantime he is pursuing another application. His team has come up with a way to use these circuits to store data, creating digital memory that is far more compact than conventional memory and which can also retrieve data more quickly. This makes it perfect for systems that handle huge databases, such as internet search engines, Ditto says. The fruits of this work should go live this year, in the form of a chaotic search engine for a commercial customer's private use.

The idea of chaotic computing emerged from a chance meeting in 1997. Ditto, then working at Georgia Institute of Technology in Atlanta, was at a conference in Bangalore, India, when he bumped into Sudeshna Sinha, who was studying non-linear dynamics at the Institute of Mathematical Sciences in Chennai. As they talked, it emerged that they were both intrigued by other researchers' attempts to adapt quantum mechanics and DNA chemistry to perform traditional computing tasks, and they began to wonder whether chaos could offer any advantages.

Chaotic behaviour is all around us - in the way that rivers flow and weather evolves, for example. While the behaviour of such systems is inherently unpredictable over all but the shortest timescales, they are not random. Their unpredictability arises because they are sensitive to the smallest of influences. Tiny fluctuations get amplified and eventually dominate the system. As chaos pioneer Edward Lorenz put it, the flap of a butterfly's wings in Brazil could set off a tornado in Texas. This is a problem for long-term weather forecasters, but Ditto and Sinha reasoned that if they could construct a circuit that behaved in a chaotic manner, then they might be able to use this sensitivity to their advantage. On a whim, they began to sketch out a design.

Deliberately creating chaos rather goes against the grain for electrical engineers. Though students are often taught how to build circuits that behave chaotically, this is for one reason only: so that they will know how to avoid chaotic behaviour in the circuits they design later in their careers. The challenge is that chaotic signals can form spontaneously in devices like amplifiers, seeded by nothing more than background noise. This produces an oscillating current that can quickly swamp the desired signal. Because of the apparent randomness of their output, these circuits are sometimes used in random number generators. Ditto reasoned, however, that beneath the chaos the output is cycling through a set of predictable voltages, and by nudging the circuit he ought to be able to stabilise it into any one of a number of states. This could be used to construct a logic gate.

Logic gates are the building blocks of computer processors. There are several types, each one producing a different digital output from a particular combination of 1s or 0s that it receives at its inputs. A NOR gate, for example, generates an output of 0 with any input values, unless both are 0. If Ditto and Sinha could mimic such behaviour by stabilising the oscillations in a chaotic circuit, it could bring some unique advantages. Stabilise the chaos in one particular pattern and they might be able to create the equivalent of a NOR gate. Stabilise it in a different pattern and they might get the equivalent of a NAND gate, which outputs a 1 unless both inputs are 1.

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