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Comment by monochromatic | Hacker News Reader

Slightly off topic, but my favorite units for c are feet per nanosecond. In those units c = 1 (plus or minus a couple of percent).

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No mention of the foot per nanosecond is complete without this seminal scene between the great, late Grace Hopper and David Letterman: https://youtu.be/1-vcErOPofQ?t=4m43s

It's even closer if you use a 'metric foot' of exactly 30 cm. Then you're only off by 0.1%.

> metric foot

Why is that a thing?

Not sure, but most of those 'metricised' units are leftovers from Napoleon's push to make everything metric.

Maybe because 30cm is very close to 12 inches.

Which leads to my favorite way to think about it. One foot per clock tick of a 1Ghz processor.

Does this mean circuits in a 1 GHz processor can't be longer than 12 inches?

No information can travel more than a foot (11.8 inches) in a nanosecond. Grace Hopper used to give a talk where she held up a piece of wire that was that long to illustrate this limitation. [1]

The first Cray computers were designed in a cylindrical shape to keep the signal wires short. [2]

[1] https://www.youtube.com/watch?v=JEpsKnWZrJ8

[2] https://en.wikipedia.org/wiki/Cray-1

'twas an annular shape!

Ok..the backplane was annular

That's really interesting - only about 2% off.

Conversion Here: https://www.wolframalpha.com/input/?i=speed+of+light+in+feet...

Mine are gigahertz * inches. 11.8ghz * in is the speed of light. Gives you a feel for it and is practical. Want to find an antenna length? Ghz*inches are your friend.

That is great, never heard that one. Thanks

I always like the fact that there are π seconds in a nanocentury (within half a percent)

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