When a user interacts with a computer, he or she provides input for it (see Figure 1.1). In response, the computer processes the input returning (hopefully) valuable output to the user. Input can be in the form of commands given, text and numbers typed, and images scanned. Output could be the results of spreadsheet calculations, a letter printed out on a printer, or a car moving onscreen during a racing car game.

Figure 1.1. Input is processed and is returned as output.

For the user to provide input, the computer has several input devices as part of its hardware—the keyboard and the mouse being the most familiar.

To the user, output is ...

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