Reading on core memory. What a fascinating way of storing bits, by weaving wire through rings.
Here are some interesting links on the topic:
*The Charming Genius of the Apollo Guidance Computer - Brian Troutwine https://www.youtube.com/watch?v=xY45YE7ggng
* Examining the core memory module inside a vintage IBM 1401 mainframe http://www.righto.com/2015/08/examining-core-memory-module-inside.html
* Arduino core memory shield https://www.tindie.com/products/kilpelaj/core-memory-shield-for-arduino/