The 'confusion' as to whether the "K" prefix meant a factor of 10^3 or 2^10 goes back decades.
In 1961 a book says "it is more usual to express the speed in bits or kilobits (1,000 bits) per second"; an IBM 1410 manual says ""The 40K core array requires 40,000 valid five-position addresses from 0,000 to 39,999." In 1962 an ACM paper referred to a "4K IBM 1401" which had 4000 characters of storage, but in 1964 Amdahl wrote a paper that had 1K meaning 1024. Academics went back and forth a bit it seems.
* https://en.wikipedia.org/wiki/Timeline_of_binary_prefixes
For hard drives specifically, a 1974 example has Mbytes in the 10^6 sense. Further examples often have drives using the base-10 sense of the prefix (including the first 5 ¼ inch floppy), while memory chips using the base-2 sense of the prefix.
The powers-of-1024 nomenclature of kibi/mebi/etc was introduced in 1995, with IEEE mandating SI prefixes only be used for powers-of-1000 in 1997. The IEC follows suit a couple of years later.
That's easy to explain, as a 1401 is actually a decimal computer.
> In the 1950s, "1 kilobit" meant 1000 bits:[9][10]
Because hard drives, going back to the original (the IBM 350), have used decimal prefixes.
Given what this article is about, I don't know why you're giving HD manufacturers the benefit of the doubt.
None of those mitigating/confounding factors apply to RPM, so the current lies are more blatant.
(Though it does seem somewhat relevant to point out here that a "500GB" drive usually has an accessible capacity of 500,107,862,016 bytes, implying an effective definition of 1GB=1,000,215,724 bytes, which is neither 1024^3 bytes nor 10^9, nor 10^9 rounded up to the nearest whole (binary-sized) sector. And that effective GB definition varies with drive capacity.)
KB = Kilobyte, which from SI definition of kilo means 10^3.
KiB = Kibibyte, was formaly defined later by IEC in 1998 as 2^10
OSes (Windows/Mac/Linux), are the ones doing it wrong, using 2^10 internaly, but presenting using SI prefixes.
Why does it feel like big corporations are just getting more blatantly evil these days?