What exactly is a computer? What makes it different from all of the other machines that we use today and have used in the past?

A computer  clearly is unique and nearly always easy to spot because it is a machine that does no useful work! This may seem like a cruel joke thought up by someone who knows computers, the PC in particular, all too well, but it is 100% true. In physics work is only done when a force moves its point of application through a distance and so steam engines and motor cars do useful work but a computer just gets warm. Yes, all those power stations work day and night polluting the atmosphere just to keep your PC warm. More seriously the fact that computers get warm is just a sign that we haven’t quite got it right even now. In theory there is absolutely no reason why a computer should get hot at all - but that’s another story.

So a computer is a machine that does no useful work. True but this really only narrows it down. After all a TV and a telephone satisfy the same condition and so do most electronic devices. Clearly a computer is a bit more than either of these two devices so what is the essence that makes it so different? To answer that question we have to go back in time but not as far as you might think…

Boole - the man who invented logic

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