The power of a computer does not arise from complexity. Instead, the computer has the ability to perform simple operations at an extremely high rate of speed. These operations can be combined to provide the computer capabilities that you are familiar with. Consistent with this idea, the actual design of the computer is also simple, as you will see.
LAYOUT OF THE LITTLE MAN COMPUTER
We begin by describing the physical layout of the Little Man Computer. A diagram for the Little Man Computer appears in Figure 6.1. The LMC consists of a walled mailroom, represented by the dark line surrounding the model in the diagram. Inside the mailroom are several objects: First, there is a series of one hundred mailboxes, each numbered with an address ranging from 00 to 99.
OPERATION OF THE LMC
We would like the Little Man to do some useful work. For this purpose we have invented a small group of instructions that he can perform. Each instruction will consist of a single digit. We will use the first digit of a three-digit number to tell the Little Man which operation to perform. In some cases, the operation will require the Little Man to use a particular mailbox to store or retrieve data (in the form of three-digit numbers, of course!)
AN EXTENDED INSTRUCTION SET
The instructions that we have defined must always be executed in the exact sequence specified. Although this is sufficient for simple program segments that perform a sequence of operations, it does not provide any means for branching or looping, both constructs that you know are very important in programming.
The workings of the computer can be simulated by a simple model. The Little Man Computer model consists of a Little Man in a mailroom with mailboxes, a calculator, and a counter. Input and output baskets provide communication to the outside world. The Little Man Computer meets all the qualifications of a von Neumann computer architecture.
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