How long is a Nanosecond in electronics?

Watch this classic clip featuring Grace Hopper to learn how long a nanosecond is. And why it is so useful as an educational tool. I still use that today whenever I do the 3-day signal integrity training course.

And happy 107 year birthday to Grace Hopper (December 9, 1906 – January 1, 1992). Such an inspiring person.

Background

Grace Hopper joined the U.S. Navy during World War II and was assigned to program the Mark I computer. She continued to work in computing after the war, leading the team that created the first computer language compiler, which led to the popular COBOL language. She resumed active naval service at the age of 60, becoming a rear admiral before retiring in 1986.

Did you know?

Grace Hopper appeared on television with David Letterman in 1986, during which she explained nanoseconds and picoseconds to her host.

We will always remember her for this ultimate answer to: “How long is a nanosecond?”

In electronics

When switching from speed of light in a vacuum to the speed of an electric signal on a printed circuit board as we use it in electronics, remember the velocity is reduced by the square root of the relative dielectric constant:

\(v = \frac{c}{\sqrt{\varepsilon_r}}\)

So when we ask “how long is a nanosecond?” in electronics, the answer is more like around 145mm depending on the exact DK/e_r of the PCB material.