Computing pioneer Grace Hopper, inventor of the compiler, searched for a concrete way to create an intuitive understanding of just how fast is a nanosecond, a billionth of a second, which was the speed of their new computer circuits. As an illustration she settled on the length of wire that is as long as light can travel in one nanosecond. The length is a very portable 11.8 inches. A microseconds worth of wire is a still portable, but a much bulkier 984 feet. In one millisecond light travels 186 miles, which only Hercules could carry. In today's terms, at a 3.06 GHz clock speed, there's .33 nanoseconds between ticks, or 3.73 inches of light travel.
Understanding the profligate ways of programmers, she suggests that every programmer wear a necklace of a microseconds worth of wire so they know what they are wasting when they throw away microseconds. And if a General is busting your chops about satellite messages taking too long to send, you can bust out your piece of wire and explain there's a lot of nanoseconds between here and there.
Here's a short, witty, and wise video of her famous nanosecond demonstration. An amazing lady, great innovator, an engaging speaker, and an inspiring teacher.