Repost. Sans tag 1st time round :-(.
I think this was in hackaday but I've quoted the actual page below.

Implementing core memory using "Flipdots" -  old tech meets older tech

http://www.vagrearg.org/content/flipcoredotmemory


They say:

Ohm2013 <http://ohm2013.org/> was at the start of August. I had a chat with
Erik, who runs Electrologica <http://www.electrologica.nl/>, about computer
history and flipdots. At one stage I was explaining how the flipdots work
and he made a rather good remark: "*that is just like core-memory*".

Why didn't *I* think of that before? He was absolutely right.
Core-memory<https://en.wikipedia.org/wiki/Core_memory> uses
a square hysteresis loop core to record the direction of the magnetic field
for storing ones and zeros. A flipdot uses a square hysteresis loop magnet
to flip the dot (the dot is also called *disc* which is a permanent
magnet). All that remained after that chat was to try it out and see if it
could be done. ...

Work in progress, August 2013.
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