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edge in speed makes it possible to simulate in real time much of what the brain does, although the basic designs are different.

There is no question that artificial intelligence will grow as the processing power and storage capability of computer chips increase. But can chip-based intelligence reach the full power of the human brain? According to Hans Moravec, that goal would require micro- processors running at 100 million MIPS50,000 times faster than a Pentium chipsupported by memory chips that store 100 million megabytes.Todays most sophisticated computers, such as the unit that currently holds the worlds speed recordthe Earth Simulator com- puter in Japan, which models our planets global behaviorare ap- proaching this kind of speed. Even the Earth Simulator, however, is not remotely likely to form the brain of a mobile being: It cost about $500 million and occupies an entire building. The trick is to achieve the requisite speed in a tiny, low-power microprocessor chip.While that might seem a fantastic extension of what a Pentium chip can do, the pace of improvement has been staggering, with chip speeds roughly doubling every 18 months, so there is hope that the appro- priate level can be achieved with our present silicon technology, per- haps in the 2020s as Moravec predicts.

But improvements in nanoscale silicon technology might run into roadblocks set by the behavior of matter at microscopic scales, which scientists do not fully understand, or by engineering problems, such as dealing with the heat thrown off by myriad transistors. If one of these roadblocks proves impassable, other approaches to nanoelectronics currently under study might still lead to more powerful artificial brains. A single molecule can now accomplish what a transistor does, sug- gesting the possibility of very compact processors and enormous memory banks. Scientists are also working on a new, exceedingly powerful type of computing based on quantum mechanics that might become a practical reality.

So far, these new approaches to computation are only in the ex- perimental stage. Researchers are looking at other designs for build- ing brains that bypass the limits of conventional chip technology, hoping to match the effectiveness of natural brain processes. One al-

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