In this lecture, I'll describe how computers work, and introduce some ideas from computer science. You won't be expected to know how a computer works for Finals. However, it's worth doing so because: they're useful tools; the mind-as-computer metaphor has invaded psychology, and you'll find pieces of jargon from it; and many researchers believe that thought is computation, and that a simulation of thought would itself be thinking. Compare e.g. a simulation of an ice-cream factory, which may be isomorphic to the real thing, but does not itself produce ice-creams.