A type of computer memory first produced as a storage medium in the mid-1970s. These devices operate as read/write memories by circulating very small polarized magnetic bubbles which represent single bits. They have the advantage of being extremely sturdy, both mechanically and in terms of their ability to operate over large temperature ranges, but they are relatively slow and expensive. They find some applications in harsh environments.
Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles, which each store one bit of data. Bubble memory started out as a promising technology in the 1970s, but failed commercially as hard disk prices fell rapidly in the 1980s.
Prehistory: Twistor memory
Bubble memory is largely the brainchild of a single person, Andrew Bobeck. Bobeck had worked on many kinds of magnetics-related projects through the 1960s, and two of his projects put him in a particularly good position for the development of bubble memory. The first was the development of the first magnetic core memory system driven by a transistor-based controller, and the second was the development of Twistor memory.
Twistor memory was based on magnetostriction, an effect which can be used to move magnetic fields. If you place a pattern on a medium (for instance, magnetic tape) and then pass a current through the tape, the patterns will slowly be "pushed" down the tape while the patterns themselves will remain unchanged. In effect it is a non-moving version of a single track from a drum memory.
Magnetic bubbles
In 1967 Bobeck joined a team at Bell Labs and started work on improving Twistor.
Starting with work on orthoferrite, Bobeck noticed an additional interesting effect: if an external field was applied to a magnetized patch of the material, the magnetized area would contract into a tiny circle, which he called a bubble.
It took some time to find the perfect material, but they discovered that garnet turned out to have the right properties.
A memory device is formed by lining up tiny electromagnets at one end with detectors at the other end.
Bubble memory is a non-volatile memory. Better yet, bubble memory devices needed no moving parts: the field that pushed the bubbles along the surface was generated electrically, whereas media like tape and disk drives required mechanical movement.
Commercialization
Bobeck's team soon had 1 cm square memories that stored 4,096 bits, the same as a then-standard plane of core memory. Not only could bubble memories replace core, but it seemed that they could replace tapes and disks as well. In fact, it seemed that bubble memory would soon be the only form of memory used in the vast majority of applications, with the high-speed market being the only one they couldn't serve.
By the mid-1970s practically every large electronics company had teams working on bubble memory. In the early 1980s, however, bubble memory became a dead end with the introduction of higher-density, faster, and cheaper hard disk systems.
Bubble memory found uses in niche markets through the 1980s in systems needing to avoid the higher rates of mechanical failures of disk drives, and in systems operating in high vibration or harsh environments.
One application was Konami's Bubble System arcade video game system, introduced in 1984. It featured interchangeable bubble memory cartridges on a Z80-based board. The Bubble System required a "warm-up" time of about 20 seconds (prompted by a timer on the screen when switched on) before the game was loaded, as bubble memory needs to be heated to around 30 to 40 °C to operate properly. The Bubble System did not prove popular, and many games originally available on the system were later released on other arcade boards with conventional ROM chips.
Sharp used bubble memory in their PC 5000 series, a laptop-like portable computer from 1983.
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