Core Memory

Magnetic-Core Memory was the predominant RAM Memory form between about 1955 to 1975. It consisted of a grid of wired ferrite toroids which could be magnetized on a clock or counterclockwise direction with a current through the right wires, and store this way a bit of information each.

Their states remain when the power is turned off, making this memory technology a non-volatile one unlike most RAMs nowadays.

Earlier Core Memories were hand wired, and later made with machines as they became smaller over time.

The Dynamic RAM (DRAM) technology replaced them starting from the 70s and made Core Memory obsolete.