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A storage device built using materials such as gadoliniumgallium garnet which are can be magnetised easily in only onedirection. A film of these materials can be created so thatit is magnetisable in an up-down direction. The magneticfields tend to join together, some with the north pole facingup, some with the south.When a veritcal magnetic field is imposed on this, the areasin opposite alignment to the field shrink to circles, or'bubbles'. A bubble can be formed by reversing the field in asmall spot, and can be destroyed by increasing the field.Bubble memory is a kind of non-volatile storage butEEPROM, Flash Erasable Programmable Read-Only Memory andferroelectric technologies, which are also non-volatile, arefaster.["Great Microprocessors of the Past and Present", V 4.0.0,John Bayko , Appendix C]