When the steam engine was invented in the eighteenth century, it began one of the greatest revolutions that have ever happened in our world. The invention of the petrol engine at the end of the nineteenth century led to another enormous change in our lives. And the computer is almost certainly going to be no less important an invention than these engines were. Just as there was a Stone Age, an Iron Age and so on, we have been living for centuries in a Paper Age, during which almost all information was kept and sent on paper; and so much of it is wasted after it has been used once that enormous numbers of trees have to be cut down every year to provide us with this paper. But now, with the computer, enormous amounts of information can be stored and sent without any paper at all, using small discs or the Internet. Computers have made it possible to do very difficult calculations very much faster than any earlier machine could. Computers also allow one to send information to others anywhere in the world, via the telephone line, and to receive information from them. One can send a very long message more quickly from England to Australia, for example, than from one's house to someone in the garden. Computers are not only used for writing; they can produce diagrams and pictures, and they can be used for playing games. One now sees them at airports and railway stations, in hotels and restaurants; in fact, almost everywhere where people gather.