Bubble memory

A magnetic bubble memory is a type of computer data storage, in which a thin film of magnetizable material is used, in which small magnetic domains, the so-called bubble ( bubbles English ) are located. Each of these bubbles stores one bit of data. The magnetic bubble memory was in the 1970s as a promising technology, but fell in the 1980s soon face the hard drives commercially behind.

Background: Twistorspeicher

The magnetic bubble memory is essentially the brainchild of a single person, Andrew Bobeck. Bobeck had worked in the 1960s on various projects related to magnetism, those two predestined him for the development of magnetic bubble memory. This was to the magnetic core memory system which was controlled via a transistor -based controller and the twistor memory.

Twistorspeicher based on magnetostriction, an effect that can be moved by the magnetization pattern. When such a pattern is for example stored on magnetic tape, is then passed through the electric current moves the pattern as a whole in the current flow direction. By placing a detector at a position over the tape, the stored information can be read out successively, without allowing the tape to move physically. So this is the Twistorspeicher around a stationary analogue of the drum store. In the 1960s, the Twistorspeicher was used by the American company AT & T in a variety of devices.

In 1967, Bobeck joined a development team of Bell Laboratories and began working on the improvement Twistorspeicher. His goal was going to construct using a material in which magnetization pattern can only move in one direction, a 2D version of the Twistorspeichers. The patterns should be written on one side of the material and then moved electrically as in Twistorspeicher. Because of the directional motility thereby would be the formation of tracks ( Tracks ) expected.

Magnetic bubbles

Bobeck began his search with ortho-ferrite material. He noticed an interesting effect: If you create a external magnetic field to a magnetization pattern in this medium, so the range is contracted into a small circle, the Bobeck as a bubble (English: bubble ) designated. These bubbles were much smaller than the magnetization of domains normal storage media such as magnetic tape, so that much higher densities appear to be possible.

After a long time, experimental garnet was found to be equipped with the best features. The bubbles formed readily and were good move. There was, however, difficult to move them selectively to read out the data to the location of the detector. Unlike the one-dimensional Twistorspeicher now two dimensions was available, and the lateral movement of the bubbles, the problem was. The solution was the application of a pattern of small magnetizable fields on the garnet surface. Upon application of a weak magnetic field, they were magnetically, and the bubbles remain in their stick one end. Through field reversal are the bubbles to the other end, transported by re- reversal to the next field in line.

A storage unit consisting of small electromagnets arrayed as the write heads at one end of the memory layer, and detectors at the other end. Enrolled bubbles migrate slowly from one end to the other, forming adjacent layers of Twistorelementen. The output of the detectors directed back to the write heads, the result is a cycle in which the information can be stored indefinitely.

History and applications

The magnetic bubble memory is a nonvolatile memory. Even if the power is cut off, the bubbles are retained, as the magnetization pattern on a disk. A further advantage is the lack of mechanical moving parts. Due to the small size of the bubbles can achieve high information density. A disadvantage, however, is the low read-out speed (access time is about 500 microseconds). Before the bubbles migrated to the detector, the information can not be read.

Bobecks team was soon able to store 4,096 bits per square centimeter, corresponding to the density of the usual at this time core memory. Thus the industry's interest was aroused to a significant extent. The magnetic bubble storage appeared as an alternative to core, magnetic tape and disk storage offering. Up to the market for high speed storage of the magnetic bubble memory promised to replace all other forms of memory.

Mid-1970s, virtually every major electronics company worked on magnetic bubble memory. Towards the end of the decade several versions in the early 1980s were on the market, and Intel launched its own 1 megabit version, the 7110th However, magnetic bubble memory proved with the introduction of the hard disk with higher information density and a shorter access time than a dead end. The development work was thus almost completely set. Only niche products, where it arrived on reliability under high mechanical stress (eg in the presence of strong vibration), were able to keep still.

One such application was the Bubble System video game system made by Konami, which was introduced in 1984. It was based on removable magnetic bubble memory cassette and a derivative of the Z80 console. Among the available games included Gradius, Attack Rush / HyperCrash / Hyper Crush and TwinBee. The magnetic bubble memory system needed a about 20 seconds long warm-up time, which was counted down on the screen before loading the game, as the memory can be optimally operated only at 30 to 40 ° C. The magnetic bubble memory system proved unpopular, and many specially produced games were produced in order for other video consoles with conventional ROM.