Why is Tarsnap pricing defined in picodollars?
There are three major reasons why Tarsnap pricing is defined in terms of picodollars per byte rather than dollars per gigabyte:
- Tarsnap's author is a geek. Applying SI prefixes to non-SI units is a geeky thing to do.
- If prices were listed in dollars per GB instead of picodollars per byte, it would be harder to avoid the what-is-a-GB confusion (a GB is 10^9 bytes, but some people don't understand SI prefixes). Picodollars are perfectly clear — nobody is going to think that a picodollar is 2^(-40) dollars.
- Specifying prices in picodollars reinforces the point that if you have very small backups, you can pay very small amounts. Unlike some people, I don't believe in rounding up to $0.01 — the Tarsnap accounting code keeps track of everything in attodollars and when it internally converts storage prices from picodollars per month to attodollars per day it rounds the prices down.