On the subject of ancient history
"The ZX80 was limited even for its time, to keep the cost very low. Other home computers at the time had 4k or more RAM."
Indeed it was, but the ZX80 could be expanded with a 3KB RAM pack which I assume provided 4KB RAM in total - or later on, it could take the 16KB RAM pack developed for the slightly more advanced ZX81.
A design classic, that RAM pack wasn't. I used multiple layers of double-sided foam sticky tape to ensure that my 16KB RAM pack didn't wobble and cause crashes when plugged in to my ZX81.