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I am building a homebrew computer using core memory. What sort of a ferrite core will I need?

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Very small ones since even a kByte reqires 8192 of them. Are you really going to string three tiny wires thru each of 8000 tiny donuts? – Olin Lathrop Mar 1 '14 at 13:47
My only alternative, transistor latches, will require more complex wiring. This project is not supposed to use ICs :D – Saad Mar 1 '14 at 13:55
I have a chuckle to myself when I read old SF books (early Asimov era stuff) and they refer to the magnetic core memories in computers running e.g. space ships. Ah, how times have moved on :-) – markt Mar 2 '14 at 1:02
up vote 4 down vote accepted

Look for a core that saturates in a low H field (lower power needed) and the core should have a wide hysteresis curve so that it stays magnetized when current is removed. No air gaps of course. Try ferroxcube, they do a good range.

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Thanks! I'll buy a couple of them to try it out. – Saad Mar 2 '14 at 5:53

You should consider to purchase an old core memory plane from an ancient computer. You could connect your own circuits to drive the plane and save the huge amount of work trying to wire up 1000's of magnetic cores. You could even just use one corner of the plane if your computer project needs a small amount of memory.

Check eBay - you can find a fair number of folks selling core memory planes. Here is one example: enter image description here

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You might find it easier using four wires through each core.

X drive Y drive

Sense and digit inhibit by using two diodes on the end of each drive wire you can reduce the number of bidirectional drivers to something like the square root of the number or x wires you then need the same for the y wires.

This will work for any number of bits ie planes in the stack. You will need a sense amplifier for each digit and a digit inhibit wire for each bit. TI use to make chips for doing the bidirectional driving.

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