I used to be an electronic technician (305x4) in the Air Force and spent 3 years on one of the old 490L Overseas AutoVon phone switches right before the DOD pha

I used to be an electronic technician (305x4) in the Air Force and spent 3 years on one of the old 490L Overseas AutoVon phone switches right before the DOD phased them out in 1987. This telephone system originally had a ferrite core memory and it was NOT non-volatile. Every few milliseconds the system had to run through each bit reading them and then re-setting them, as the magnetic field collapsed over time. The system used 50 volts.