朗文3L看听学英语第四册 Lesson 17

　　17 Television Day: Computers
　　TV Commentary:
　　... the astronauts are returning to earth at exactly 5.24. Splash-down will be in the Pacific, 427 miles west of Hawaii."
　　You have often heard announcements like this on television. Scientists can tell us exactly when a space-capsule will arrive on the moon, for instance, and exactly when it will return. They can calculate things like this to the nearest second. How do they do it? Well of course, they use mathematics. We can all do simple sums on paper, but we must use computers for extremely difficult calculations. Perhaps you have seen mechanical calculating-machines in banks and offices. They can work very quickly but nothing like computers. Computers aren't mechanical. They don't have wheels and gears in them. Instead, they work on electrical circuits and can do difficult calculations at tremendous speed. They can work 100 million times faster then the human mind!