As you can see from the illustration below, an electron head-tail pair (which we’ll call an ‘electron’) moves along a row of copper cells (which we’ll call a ‘wire’) at the rate of one cell per generation.
Wires give us a way of transporting a sequence of electrons from one point to another. The pattern of electrons is preserved as they move along a wire and so, if we can represent data using these patterns, we can use the wires to carry data from one place to another.
A simple approach is to divide a wire into segments of equal length - call this length n. If there is an electron at the start of the segment, it represents a binary ‘1’ bit; if the segment is empty, it represents a ‘0’ bit. As long as the two ends of a piece of wire are synchronised (so that the receiver knows when a segment is about to start), we can communicate data like this.
What value of n shall we use? A segment has to be big enough to hold a head and a tail, and so n must be at least 2. However, as you can easily verify, it’s necessary to have at least one gap between successive electrons, and so in fact n must be at least 3. We say that a system using a particular value of n is employing n-micron technology.
As Michael Greene has shown, it is possible to implement all the logic and other functions we need for the computer in 3-micron technology. However, except for the computer’s display (which you can see on the index page) our implementation is in the less aggressive 6-micron technology as this makes the design simpler and probably smaller. The original Scientific American article suggested using 13-micron technology.
The picture below shows some 6-micron signals.
The top wire is carrying a steady stream of zeros; the middle wire, a steady stream of ones; and the bottom wire, the sequence ‘1110’ repeating forever. The middle wire also shows how a signal can be split into two copies.
Another approach to representing data on a wire is to divide it into segments of length n and represent a binary ‘1’ by an electron at the start of the segment and a ‘0’ by an electron one cell further back: the logic state is represented by the phase of the electron relative to a fixed clock. This strategy has some attractive features, but we did not consider it until design of the the computer was well under way.
Next, the diode.
This page most recently updated Thu 26 Jul 08:28:27 BST 2018
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