two scales · 1000 and 1024 · why a drive looks smaller
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
kB, MB, GB are decimal, step 1000 (SI). KiB, MiB, GiB are binary, step 1024 (IEC 80000-13). In SI the symbol for kilo is written in lower case.
The manufacturer counts decimally, as SI requires: a terabyte is exactly 1 000 000 000 000 bytes, because kilo means a thousand in a kilogram, a kilowatt and a kilobyte alike.
Windows divides that same number by 1024 three times and labels the result "GB" — so 931 appears on screen instead of 1000. Not a single byte has gone anywhere: the ruler changed, not the amount of data.
It was precisely to tell the two rulers apart that in 1998 the IEC gave the binary steps names of their own: kibi, mebi, gibi. 931 GiB and 1 TB are the same number of bytes written in two different systems.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 5 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
