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Phone Switches: Back To The Future


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PHONE SWITCHES: BACK TO THE FUTURE

For years, telephone companies routed calls with so-called crossbar switches--noisy antiques filled with springs and magnets. The switches were built around grids of horizontal and vertical lines; the path of a phone call was established when two lines were electrically connected at a cross point. While phone companies long ago began replacing crossbar switches with electronic ones, the crossbar concept has lived on in the computer world.

On May 6, Digital Equipment Corp. announced that it is using a crossbar design at the heart of its new GIGAswitch, a device for moving data rapidly among computers. But instead of springs and magnets, the critical elements in the GIGAswitch are chips that can pass along 100 million bits of data per second. For DEC, the beauty of a crossbar switch is that it can handle simultaneously several streams of data following different paths through the grid--similar to the parallel processing that many supercomputers do. Its theoretical capacity: 3.4 billion bits per second. Not bad for an antique.EDITED BY PAUL M. ENG


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