A storage device built using materials such as gadolinium gallium garnet which are can be magnetised easily in only one direction.
A film of these materials can be created so that it is magnetisable in an up-down direction.
The magnetic fields tend to join together, some with the north pole facing up, some with the south.
When a veritcal magnetic field is imposed on this, the areas in opposite alignment to the field shrink to circles, or 'bubbles'.
A bubble can be formed by reversing the field in a small spot, and can be destroyed by increasing the field.
Bubble memory is a kind of non-volatile storage
, Flash Erasable Programmable Read-Only Memory
and ferroelectric technologies, which are also non-volatile, are faster.
["Great Microprocessors of the Past and Present", V 4.0.0, John Bayko <email@example.com>, Appendix C]