> Stuff like DRAM storing a 0 or 1 via the presence or absence of 40K electrons

I'd assume that these days it's a couple of orders of magnitude fewer than that (the cited source is from 1996). Incidentally, 40k e- is roughly the capacity of a single electron well ("pixel") in a modern CMOS image sensor [1] – but those 40k electrons are able to represent a signal of up to ~14 bits, around 10k distinct luminance values, depending on temperature and other noise sources.

[1] https://www.princetoninstruments.com/learn/camera-fundamenta...