When people try to explain CPU speed, they often make a comparison to cars. As far as I can tell, there are two reasons for this. The first makes some kind of sense: it’s because the central processing unit ‘powers’ a computer – not in the sense of providing energy, but of determining how fast it can go – and is available running at a range of speeds, just as cars are powered by engines available in a variety of sizes. The second reason is that most technology writers are male and like cars. There are some who don’t like cars, but even they see them as the kind of thing the mythical everyman likes and thus are suitable to be deployed in explanatory metaphors.