--- Adam Thompson wrote:
I can't find any derivation for why we call a 2.75" drive a 2.5" drive, since there's no such thing as a 2.5" floppy[1]! Perhaps the internal platter is 2.5" wide?
Yup. At least they were, manufacturers started shrinking them.
As for lumber: a 2x4 used to be 2" by 4". But that was a rough sawn surface. Today rough cut lumber is 2"x4". Finished lumber used to have 1/8" planed off each face to make it smooth. That made it 1.75"x3.75". Then someone got cheap and decided to sell 1.5"x3.5" lumber, and call it 2x4.
Same with wire gauge. Originally 16 gauge wire was 1/16" diameter. That is 0.0625", but now what is sold as 16 gauge is 0.0508", so 1/19.7". The standard states 16 gauge is "19.7 turns of wire per inch (no insulation)".
Everything is a rip-off, but what are you going to do when it's built into the standards? As long as they're consistent...
Rob Dyck