Magnetic bubble memory is a non-volatile data storage medium invented at Bell Labs in 1967. Bubble memory uses a thin magnetic film on a garnet substrate, which forms cylindrical domains when constricted under a magnetic field. These domains, or bubbles, each store one bit of data. The bubbles are created by a generator signal, pushed around the film in racetrack-like loops, and eventually detected by a sense amplifier. Unlike semiconductor memories, bubble memory is sequential access, rather than random access. Conceptually, it is like a tiny magnetic diskette and drive, but with no moving parts. Instead of the disk moving, the bits move.
Bubble memory was a promising technology that was positioned to replace all other forms of memory, but was quickly outpaced by semiconductor memory (speed and cost) and hard disk drives (capacity and cost). The computer industry was already shaped around a well-established split between fast, small-capacity main memory and slower large-capacity storage, and bubble memory was squeezed out in both categories as a costlier, inferior alternative.
Bubble memory may still be occasionally used in some military and industrial applications, where extreme ruggedness and nonvolatility are a requirement. Bubble memory is inherently radiation-hardened: it can withstand the photoelectric effects of a nuclear event, when implemented with specialized nonstop logic circuits which prevent partial loop rotation.
Former manufacturers of magnetic bubble memory include Hitachi, Intel, Motorola, Rockwell and Texas Instruments. Recently, IBM has re-branded the bubble memory concept as 'racetrack' memory, a sort of nano-scale bubble memory which uses an array of tiny wire loops to carry the magnetic domains.
