Comment by theamk

what do you mean?

Memory and i/o ports are in separate address spaces in Z80, but for use cases described in post ("dot product for 1536-bit vectors") i/o port space does not matter, it's all memory - and there is just a single address space there.

(Granted, some Z80-based systems had funky paging setup, but author makes no mention of those, they just say generic Z80 - and that means total 64KB for code, input data, cache and output data)