The Virtual Computer

This essay is about computers. Probably not in the way you're used to thinking about computers. It won't be about RAM and ROM and disk drives. Instead it'll be an extreme close up view of the stuff that lies at the heart of modern computers--digital logic. Integrated circuits are what computers are made of and digital logic is what integrated circuits are made of. If you said digital logic to computer engineers, they'd immediately think of electronics. However, in this essay we're going to take an unusual step sideways. We'll ignore electronics almost completely and instead show how digital logic can be conjured up with some simple games, where the most complicated thing going on is counting.

The example here is a three bit binary counter. Click Start to see it go. Each bit changes state half as often as the one above it. The state is kept in the loop on the right of each bit. An "electron" circulating indicates a "one", no electron a "zero". Details of this and other "circuits" will be explained as we go.

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Brian Silverman
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