INVITATION TO CYBERSECURITY 6 is awe-inspiring. Because of these feats, sometimes we think of them as having a more powerful “brain” than we have. But computers, in reality, are very limited machines, and it is our intelligence that makes them useful by contextualizing their input and output. 2.1.1 Boolean Logic “‘Contrariwise,’ continued Tweedledee, ‘if it was so, it might be; and if it were so, it would be; but as it isn’t, it ain’t. That’s logic.’” - Through the Looking-Glass by Lewis Carroll Computers are only capable of doing one basic kind of thing: performing simple Boolean logic operations. Boolean logic, devised by George Boole in 1847, is a system that accepts true and false inputs and produces a true or false output. In the 1930s, Claude Shannon, a pioneer of computing, discovered the relationship between Boolean logic and digital circuits. He proved a circuit can be created to model (and, therefore, solve) any Boolean logic equation. A circuit is a path through which electricity flows. What this means is a computer can accept binary inputs, represented by the symbols 1 for true and 0 for false, and can produce binary outputs (see Figure 2.1). That is it. That is fundamentally what computers can do. It is even a misnomer to say computers can do anything—as if they had a mind and will of their own. Essentially, they are an encapsulation of wires and switches that are configured to either admit or deny an electrical charge (1 and 0 in binary, respectively). So more accurately, they are passive—they are a machine through which electricity flows. Figure 2.1 The binary input and output combinations for three foundational Boolean logic operations: AND, Inclusive OR, and Exclusive OR (XOR). The twin marvels of computers that enable them to produce extraordinary results are how incredibly tiny their wiring and switches are, and how incredibly quickly electricity flows through them. Both of these phenomena are literally incomprehensible to us because our human senses operate on much larger and slower scales. The wiring of a computer is encapsulated in cleverly organized transistors that form circuits that perform all of the necessary Boolean logic operations and store the results. A transistor is a device that can control the flow of electricity. Transistors are so small that millions of them can fit inside the period at the end of this sentence. Read the previous sentence again—incomprehensible!
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