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Circuits of Magic (finally, March/April) made me laugh. The article describes Professor Andy van Dams use, in the 1970s, of hand-built relay computers to teach computer-hardware logic. What amused me was the authors characterization that this heap of wires and circuitry hails from the prehistoric period of the digital agethe 1970s.

To use relay computers to demonstrate the logic of computer hardware was very clever of Professor van Dam. But they could well have been used for the same purpose when I took my first class on computing at Brown in 1957. Relay computing is a technique from the late 1930s. It was first proposed by Claude Shannon in 1937 as a way of using Boolean logic for building computers and was implemented in the Harvard Mark I computer, whose construction started in 1939.

To consider even the 1930s as the prehistoric period of the digital age seems a bit far-fetched when there is evidence that a mechanical astronomical computer, which used gears and was called the Antikythera Mechanism, was built more than 2,000 years ago by the ancient Greeks. Even the Internet and integrated circuits appeared before the 1970s. In fact, before the 1970s we had almost everything you see in computers today, except that it all was much bigger, much slower, and much more expensive.

Here in the twenty-first century, computer hardware is still based on circuits implementing Boolean Logic. And each of those many millions of transistors on the computer chip in your PC is still just acting as a relay, to perform the good old Ands, Ors, and Nots of Boolean logic.

Alvin Mullery 58

Belvdre, France

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