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Comments
I worked on missile fire control system with core memory in the navy. I won’t say which navy. It was possible to repair broken bits by rewiring a new core. I never had to do that, though.
How would they break? Wires and ferrite doughnuts would not seem like simething that can burn out easy. On the other hand the board that I have seems to have been patched numerous times - all in the process of making it I thought.
well as i said i never had to actually do it … i think the issue might have been the magnetic properties of the little ferrite cores. also a navy destroyer is a pretty hostile environment, it might be possible for one to be physically damaged in while being held in spares.
It was possible to make some core memories malfunction and/or disintegrate. As you operate the core, you push the ferite (iron oxide) around the B-H curve (Hysteresis Loop). If you do it fast enough, several 'Bad things' can happen. First you heat the core itself due to the hysteresis losses. The B-H curve is actually temperature sensitive.
If you make a ferromagnetic material hot enough (Curie point), it ceases to be ferromagnetic.
So if you heat the core enough, you can push it right off the curve, and get a parity error or worse. I actually did that to a Honeywell mainframe once. I had a program to calculate pi that I ran in the middle of night when nobody cared. One night after about 2 hours, the machine crashed due a memory parity. The error was a memory reference from my pi calculator. That was the last time I ran the program on that computer system.
Some companies also used a temperature sensitive 'glue' to hold the ferrite together. I don't know for a fact, but I was told that this actually resulted in catastrophic failure in some 3rd party large core storage systems on S/360. The core simply disintegrated when it got to hot!
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