Imagine you’re shopping for a new car, and the salesperson says, “Did you know, this car doesn’t just drive on the road.”
“Oh?” you reply.
“Yeah, you can also use it to do other things. For instance, it folds up to make a pretty good bicycle. And it folds out to make a first-rate airplane. Oh, and when submerged it works as a submarine. And it’s a spaceship too!”
You’d assume the salesperson was joking. But we take a comparable flexibility for granted in our computers. We can use the same machine to fly past the Statue of Liberty with a flight simulator, make financial projections using a spreadsheet, chat with friends on Facebook, and do many other things. It’s very nearly as astonishing as a single machine that works as a car, bicycle and spaceship.
Two characteristics of computers make this flexibility possible. First, computers are programmable. That is, by inputting an appropriate sequence of instructions, we can change a computer’s behavior. Second, computers are universal. That is, with the right program we can make a computer perform any algorithmic process whatsoever, as long as the machine has enough memory and time.
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