I did find a description of bubble memory:
A type of non-volatile memory composed of a thin layer of material that can
be easily magnetized in only one direction. When a magnetic field is
applied to circular area of this substance that is not magnetized in the
same direction, the area is reduced to a smaller circle, or bubble.
It was once widely believed that bubble memory would become one of the
leading memory technologies, but these promises have not been fulfilled.
Other non-volatile memory types, such as EEPROM, are both faster and less
expensive than bubble memory.
- John Higginbotham
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limbo.netpath.net