How many registers will we need to put into Simon to store information? We shall need one register to read the input tape and to store the number or operation recorded on it. We shall call this register the _input register I_. We shall need another register to store the number or operation that Simon says is the answer and to give it to the output lights. We shall call this register the _output register O_. We shall need 5 registers for the part of Simon which does the computing, which we shall call the _computer_: we shall need 3 to store numbers put into the computer (_C_1, _C_2, _C_3), 1 to store the operation governing the computer (_C_4), and 1 to store the result (_C_5). Suppose that we decide to have 8 registers for storing information, so as to provide some flexibility for doing problems. We shall call these registers _storage registers_ and name them _S_1, _S_2, _S_3, ··· _S_8. Then Simon will have 15 registers: a memory that at one time can hold 15 pieces of information. How will one of these registers hold information? For example, how will register _S_1 hold the number 2 (see Fig. 3)? The number 2 in machine language is 10. Register _S_1 consists of two relays, _S_1-2 and _S_1-1. 10 stored in register _S_1 means that relay _S_1-2 will be energized and that relay _S_1-1 will not be energized. THE CONTROL OF SIMON So far we have said nothing about the control of Simon. Is he docile? Is he stubborn? We know what his capacity is, but we do not know how to tell him to do anything. How do we connect our desires to his behavior? How do we tell him a problem? How do we get him to solve it and tell us the answer? How do we arrange control over the sequence of his operations? For example, how do we get Simon to add 1 and 2 and tell us the answer 3? On the outside of Simon, we have said, there are two ears: little mechanisms for reading punched paper tape. Also there are two eyes that can wink: light bulbs that by shining or not shining can put out information (see Fig. 1). One of the ears—let us call it the _left ear_—takes in information about a particular problem: numbers and operations. Here the _problem tape_ or _input tape_ is listened to. Each line on the input tape contains space for 2 punched holes. So, the information on the input tape may be 00, 01, 10, or 11—either a number or an operation. The other ear—let us call it the _right ear_—takes in information about the sequence of operations, the program or routine to be followed. Here the _program tape_ or _routine tape_ or _control tape_ is listened to. Each line on the program tape contains space for 4 punched holes. We tell Simon by _instructions_ on the program tape what he is to do with the information that we give him on the input tape. The information on the program tape, therefore, may be 0000, 0001, 0010, ···, 1111, or any number from 0 to 15 expressed in binary notation (see Supplement 2).