Free Ebook How Computers Work

Parallel computers provide the most powerful information-processing capabilities available. Like all digital computers, they represent and process information in ways that are based on simple ideas of Boolean logic. In this article we introduce those ideas and sketch the ways in which they are
implemented in the elementary circuits of electronic computers. We then discuss the principles behind the high performance—in particular, the high speed—of vector and parallel supercomputers.

Digital Information, Boolean
Logic, and Basic Operations

Suppose that an airplane is about to enter a runway for takeoff. The air traffic controller must determine, with the aid of a computer, whether the plane can safely proceed onto the run way. Has the airplane that just landed cleared the runway? Are all incoming planes sufficiently far away? The
answers to those questions—yes or no, true or false—are information of a kind that can be managed by digital computers. The two possibilities are encoded within a computer by the two possible output states of electronic devices. For instance, “Yes” or “True” can be represented by an output signal on the order of 5 volts, and “No” or “False” by a near-zero voltage level. This simple code is the basis of the more complicated codes by which information is represented in computers.

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