Fig. 2. Electronic tube.
[Figure 2] shows a simple electronic tube. It has three parts—the Cathode, the Grid, and the Plate. The Grid actually is a coarse net of metal wires. Electrons can flow from the Cathode to the Plate, provided the voltage on the Grid is such as to permit them to flow. So we can see that an electronic tube is a very simple on-off device and expresses a “yes” or a “no,” a 1 or 0, a binary digit, a unit of information. A simple electronic tube suitable for calculating purposes costs 50 cents to a $1, only ⅒ the cost of a relay. It can be changed from 1 to 0, or back again, in 1 millionth of a second.
Relays have been widely used in the mechanical brains so far built, and electronic tubes are the essence of Eniac.
In the next chapter, we shall see how physical equipment for handling information can be put together to make a simple mechanical brain.
Chapter 3
A MACHINE THAT WILL THINK:
THE DESIGN OF A VERY SIMPLE
MECHANICAL BRAIN
We shall now consider how we can design a very simple machine that will think. Let us call it Simon, because of its predecessor, Simple Simon.
SIMON, THE VERY SIMPLE
MECHANICAL BRAIN
By designing Simon, we shall see how we can put together physical equipment for handling information in such a way as to get a very simple mechanical brain. At every point in the design of Simon, we shall make the simplest possible choice that will still give us a machine that: handles information, transfers information automatically from one part of the machine to another, and has control over the sequence of operations. Simon is so simple and so small, in fact, that it could be built to fill up less space than a grocery-store box, about 4 cubic feet. If we know a little about electrical work, we will find it rather easy to make Simon.
What do we do first to design the very simple mechanical brain, Simon?