It was earlier than the 90s, and came with popular 8-bit CPUs in the 80s. The Z-80 microprocessor could address 64kb (which was 65,536 bytes) on its 16-bit address bus.

Similarly, the 4104 chip was a "4kb x 1 bit" RAM chip and stored 4096 bits. You'd see this in the whole 41xx series, and beyond.

> The Z-80 microprocessor could address 64kb (which was 65,536 bytes) on its 16-bit address bus.

I was going to say that what it could address and what they called what it could address is an important distinction, but found this fun ad from 1976[1].

"16K Bytes of RAM Memory, expandable to 60K Bytes", "4K Bytes of ROM/RAM Monitor software", seems pretty unambiguous that you're correct.

Interestingly wikipedia at least implies the IBM System 360 popularized the base-2 prefixes[2], citing their 1964 documentation, but I can't find any use of it in there for the main core storage docs they cite[3]. Amusingly the only use of "kb" I can find in the pdf is for data rate off magnetic tape, which is explicitly defined as "kb = thousands of bytes per second", and the only reference to "kilo-" is for "kilobaud", which would have again been base-10. If we give them the benefit of the doubt on this, presumably it was from later System 360 publications where they would have had enough storage to need prefixes to describe it.

[1] https://commons.wikimedia.org/wiki/File:Zilog_Z-80_Microproc...

[2] https://en.wikipedia.org/wiki/Byte#Units_based_on_powers_of_...

[3] http://www.bitsavers.org/pdf/ibm/360/systemSummary/A22-6810-...

Even then it was not universal. For example, that Apple I ad that got posted a few days ago mentioned that "the system is expandable to 65K". https://upload.wikimedia.org/wikipedia/commons/4/48/Apple_1_...