What follows should be skipped unless you are interested in these questions and the burdensome details needed for answering them.
SIMON’S THINKING—
TRANSFERRING INFORMATION
The first basic thinking operation for any mechanical brain is transferring information automatically. Let us see how this is done in Simon.
Fig. 4. Scheme of Simon.
Let us first take a look at the scheme of Simon as a mechanical brain ([see Fig. 4]). We have 1 input, 8 storage, 5 computer, and 1 output registers, which are connected by means of transfer wires or a transfer line along which numbers or operations can travel as electrical impulses. This transfer line is often called the bus, perhaps because it is always busy carrying something. In Simon the bus will consist of 2 wires, one for carrying the right-hand digit and one for carrying the left-hand digit of any number 00, 01, 10, 11. Simon also has a number of neat little devices that will do the following:
When any number goes into a register, the coils of the relays of the register will be connected with the bus.
When any number goes out of a register, the contacts of the relays of the register will be connected with the bus.
For example, suppose that in register C5 the number 2 is stored. In machine language this is 10. That means the left-hand relay (C5-2) is energized and the right-hand relay (C5-1) is not energized. Suppose that we want to transfer this number 2 into the output register O, which has been cleared. What do we do?
Let us take a look at a circuit that will transfer the number ([see Fig. 5]). First we see two relays in this circuit. They belong to the C5 register. The C5-2 relay is energized since it holds 1; current is flowing through its coil, the iron core becomes a magnet, and the contact above it is pulled down. The C5-1 relay is not energized since it holds 0; its contact is not pulled down. The next thing we see is two rectifiers. The sign for these is a triangle. These are some modern electrical equipment that allow electrical current to flow in only one direction. In the diagram, the direction is shown by the pointing of the triangle along the wire. Rectifiers are needed to prevent undesired circuits. Next, we see the bus, consisting of two wires. One carries the impulses for left-hand or 2 relays, and the other carries impulses for the right-hand or 1 relays. Next, we see two relays, called the entrance relays for the O register. Current from Source 1 may flow to these relays, energize them, and close their contacts. When the first line of the program tape is read, specifying the receiving register, the code 1111 causes Source 1 to be energized. This fact is shown schematically by the arrow running from the program tape code 1111 to Source 1. Finally, we see the coils of the two relays for the Output or O register. We thus see that we have a circuit from the contacts of the C5 register through the bus to the coils of the O register.