https://youtu.be/FU_YFpfDqqA?si=NRQYXa6nk_NTn7vf
I believe it was this video by Veritasium that I was thinking of that explains how we got switches to think. Modern computers use the same principles. Just instead of physical switches, they use semiconductor switches. Which is were the rocks come into play. Semiconductors, in supper brief nut shell, are on the verge of conducting and need a little nudge of voltage to start conducting. Hence the semi part.
Absolutely love Rogue Trader