>The reason I asked because I can't figure out how you can get
persistent memory without burning circuits. An internal battery
perhaps or a writable crystal, but.... how?
In the early 1970's, the computer industry went from magnetic core (
https://en.wikipedia.org/wiki/Magnetic-core_memory ) to static and dynamic RAM, losing non-volatility in the process. It was possible to run a CMOS static RAM on a tiny battery, to maintain data when the main system power was turned off.
The industry developed UV-erasable EPROM as a substitute, which allowed only the erasure of the entire memory chip, , and some early EEPROM. (Electrically erasable programmable Read-Only-Memory).