Don’t forget Grace Hopper (1906 – 1992), American computer scientist, mathematician, and United States Navy rear admiral.

> Hopper became known for her nanoseconds visual aid. People (such as generals and admirals) used to ask her why satellite communication took so long. She started handing out pieces of wire that were just under one foot long—11.8 inches (30 cm)—the distance that light travels in one nanosecond. She gave these pieces of wire the metonym "nanoseconds." She was careful to tell her audience that the length of her nanoseconds was actually the maximum distance the signals would travel in a vacuum, and that signals would travel more slowly through the actual wires that were her teaching aids. Later she used the same pieces of wire to illustrate why computers had to be small to be fast. At many of her talks and visits, she handed out "nanoseconds" to everyone in the audience, contrasting them with a coil of wire 984 feet (300 meters) long, representing a microsecond. Later, while giving these lectures while working for DEC, she passed out packets of pepper, calling the individual grains of ground pepper picoseconds.

https://en.wikipedia.org/wiki/Grace_Hopper

Why not just make them 27cm and then you get the true distance signals travel?

Maybe because speed of light is more approachable to a general audience, and maybe because she’s making a point about absolute upper bounds for all possible signals and didn’t want to reference something that could be improved, or because signal speed depends on the medium and maybe she didn’t feel like rat-holing on materials to make a point about speed of light? Light signals travel at light speed through space. 27cm works for electrical signals but not optical signals in fiber or space, nor other signal types. 30cm as a bound always works, and happens to be a nice round number too, more memorable… I see a lot of reasons why not just. :P

Great content from Jeff Dean slides. Since they are dating from 2009, I wonder what are the things he had changed his mind of.

a well documented rabbit hole