    3

    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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