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Conventional computers deal with information the way a
railroad switching yard deals with box cars. A train a half-mile long
arrives at one end of the yard in Chicago dragging cars destined for
Boston, Washington, Philadelphia and New York. The trains on tracks
next to it are also a jumble of cars headed for Boston, Washington,
Philadelphia and the Big Apple. The trick the yard handlers have
ahead of them is to take each train apart, couple all the cars headed for
New York to one locomotive, and send that locomotive on its way.
At one end of the yard are twenty parallel tracks of trains waiting
to be disassembled. At the other are twenty parallel tracks of trains
that have been put back together and are preparing to depart. But the
critical process takes place on one narrow set of tracks in the center of
the yard where all the breaking down and reassembling is done. And
each incoming train must wait its turn to get onto that slender stretch
of working track.
A conventional computer also stores a sizeable batch of
information in a kind of holding pen, but has to shoot it, one small bit
at a time, through a processor where the real work of computation and
comparison are accomplished--this is called serial processing.
Neural nets function in a radically different way. They don't use
the narrow, railroad-track approach to information processing.
Instead, they are shaped like spider webs which process information in
parallel. The lines of the webs are electrical channels whose
conductivity can be raised or lowered. The junctions where the lines
meet are switches that can be turned on or off.
Neural nets can solve problems by making rough models of the
real world as they learn from data we give them. Here's how you'd
solve the salesman's dilemma using a neural net. You'd pick ten
junction points on the web to represent ten cities. You'd adjust the
conductivity of the lines between them in a manner proportional to the
distance between them. (If two cities are one hundred miles apart, for
example, you'd set the resistance to one ohm. If they're two hundred
miles apart, two ohms. Three hundred miles, three ohms.) You'd turn
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