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Bubble memory is a type of
non-volatile Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typi ...
computer memory In computing, memory is a device or system that is used to store information for immediate use in a computer or related computer hardware and digital electronic devices. The term ''memory'' is often synonymous with the term '' primary storag ...
that uses a thin film of a magnetic material to hold small magnetized areas, known as ''bubbles'' or ''domains'', each storing one bit of data. The material is arranged to form a series of parallel tracks that the bubbles can move along under the action of an external magnetic field. The bubbles are read by moving them to the edge of the material, where they can be read by a conventional magnetic pickup, and then rewritten on the far edge to keep the memory cycling through the material. In operation, bubble memories are similar to
delay-line memory Delay-line memory is a form of computer memory, now obsolete, that was used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay-line memory was a refreshable memory, but as opposed to modern ran ...
systems. Bubble memory started out as a promising technology in the 1970s, offering
memory density Density is a measure of the quantity of information bits that can be stored on a given length (''linear density'') of track, area of surface (''areal density''), or in a given volume (''volumetric density'') of a computer storage medium. General ...
of an order similar to
hard drives A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magn ...
, but performance more comparable to core memory, while lacking any moving parts. This led many to consider it a contender for a "universal memory" that could be used for all storage needs. The introduction of dramatically faster
semiconductor memory Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to devices in which data is stored within metal–oxide–semiconductor (MOS) memory cells on a si ...
chips pushed bubble into the slow end of the scale, and equally dramatic improvements in hard-drive capacity made it uncompetitive in price terms. Bubble memory was used for some time in the 1970s and 1980s where its non-moving nature was desirable for maintenance or shock-proofing reasons. The introduction of flash storage and similar technologies rendered even this niche uncompetitive, and bubble disappeared entirely by the late 1980s.


History


Precursors

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 Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core. Core memory uses toroids (rings) of a hard magnet ...
system driven by a
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
-based controller, and the second was the development of twistor memory. Twistor is essentially a version of core memory that replaces the "cores" with a piece of
magnetic tape Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnet ...
. The main advantage of twistor is its ability to be assembled by automated machines, as opposed to core, which was almost entirely manual.
AT&T AT&T Inc. is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company by revenue and the third largest provider of mobile ...
had great hopes for twistor, believing that it would greatly reduce the cost of computer memory and put them in an industry leading position. Instead,
DRAM Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxid ...
memories came onto the market in the early 1970s and rapidly replaced all previous
random-access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the ...
systems. Twistor ended up being used only in a few applications, many of them AT&T's own computers. One interesting side effect of the twistor concept was noticed in production: under certain conditions, passing a current through one of the electrical wires running inside the tape would cause the magnetic fields on the tape to move in the direction of the current. If used properly, it allowed the stored bits to be pushed down the tape and pop off the end, forming a type of
delay-line memory Delay-line memory is a form of computer memory, now obsolete, that was used on some of the earliest digital computers. Like many modern forms of electronic computer memory, delay-line memory was a refreshable memory, but as opposed to modern ran ...
, but one where the propagation of the fields was under computer control, as opposed to automatically advancing at a set rate defined by the materials used. However, such a system had few advantages over twistor, especially as it did not allow random access.


Development

180px, Bubble domain visualization by using CMOS-MagView In 1967, Bobeck joined a team at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mul ...
and started work on improving twistor. The
memory density Density is a measure of the quantity of information bits that can be stored on a given length (''linear density'') of track, area of surface (''areal density''), or in a given volume (''volumetric density'') of a computer storage medium. General ...
of twistor was a function of the size of the wires; the length of any one wire determined how many bits it held, and many such wires were laid side-by-side to produce a larger memory system. Conventional magnetic materials, like the magnetic tape used in twistor, allowed the magnetic signal to be placed at any location and to move in any direction.
Paul Charles Michaelis Paul Charles Michaelis was a Bell Labs researcher in magnetic bubble memory. Education Michaelis was born June 18, 1935 in NYC, raised in New Jersey on a Scotch Plains farm, went to high School in Scotch Plain, First worked in Bell Labs, Murray Hil ...
working with
permalloy Permalloy is a nickel–iron magnetic alloy, with about 80% nickel and 20% iron content. Invented in 1914 by physicist Gustav Elmen at Bell Telephone Laboratories, it is notable for its very high magnetic permeability, which makes it useful as ...
magnetic thin films discovered that it was possible to move magnetic signals in orthogonal directions within the film. This seminal work led to a patent application. The memory device and method of propagation were described in a paper presented at the 13th Annual Conference on Magnetism and Magnetic Materials, Boston, Massachusetts, 15 September 1967. The device used anisotropic thin magnetic films that required different magnetic pulse combinations for orthogonal propagation directions. The propagation velocity was also dependent on the hard and easy magnetic axes. This difference suggested that an isotropic magnetic medium would be desirable. This led to the possibility of making a memory system similar to the moving-domain twistor concept, but using a single block of magnetic material instead of many twistor wires. Starting work extending this concept using
orthoferrite An orthoferrite is any of a class of chemical compounds with the formula RFeO, where R is one or more rare-earth elements. Orthoferrites have an orthorhombic crystal structure with a space group Pbnm and most are weakly ferromagnetic. At the Né ...
, Bobeck noticed an additional interesting effect. With the magnetic tape materials used in twistor, the data had to be stored on relatively large patches known as ''domains''. Attempts to magnetize smaller areas would fail. With orthoferrite, if the patch was written and then a magnetic field was applied to the entire material, the patch would shrink down into a tiny circle, which he called a ''bubble''. These bubbles were much smaller than the domains of normal media like tape, which suggested that very high area densities were possible. Five significant discoveries took place at Bell Labs: # The controlled two-dimensional motion of single wall domains in permalloy films # The application of orthoferrites # The discovery of the stable cylindrical domain # The invention of the field access mode of operation # The discovery of growth-induced uniaxial anisotropy in the garnet system and the realization that garnets would be a practical material The bubble system cannot be described by any single invention, but in terms of the above discoveries. Andy Bobeck was the sole discoverer of (4) and (5) and co-discoverer of (2) and (3); (1) was performed by P. Michaelis in P. Bonyhard's group. At one point, over 60 scientists were working on the project at Bell Labs, many of whom have earned recognition in this field. For instance, in September 1974, H.E.D. Scovil, P.C. Michaelis and Bobeck were awarded the
IEEE Morris N. Liebmann Memorial Award The initially called Morris Liebmann Memorial Prize provided by the Institute of Radio Engineers (IRE), the IEEE Morris N. Liebmann Memorial Award was created in 1919 in honor of Colonel Morris N. Liebmann. It was initially given to awardees who h ...
by the IEEE with the following citation: ''For the concept and development of single-walled magnetic domains (magnetic bubbles), and for recognition of their importance to memory technology.'' It took some time to find the perfect material, but it was discovered that
garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different ...
had the correct properties. Bubbles would easily form in the material and could be pushed along it fairly easily. The next problem was to make them move to the proper location where they could be read back out: twistor was a wire and there was only one place to go, but in a 2D sheet things would not be so easy. Unlike the original experiments, the garnet did not constrain the bubbles to move only in one direction, but its bubble properties were too advantageous to ignore. The solution was to imprint a pattern of tiny magnetic bars onto the surface of the garnet. When a small magnetic field was applied, they would become magnetized, and the bubbles would "stick" to one end. By then reversing the field they would be attracted to the far end, moving down the surface. Another reversal would pop them off the end of the bar to the next bar in the line. A memory device is formed by lining up tiny
electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in ...
s at one end with detectors at the other end. Bubbles written in would be slowly pushed to the other, forming a sheet of twistors lined up beside each other. Attaching the output from the detector back to the electromagnets turns the sheet into a series of loops, which can hold the information as long as needed. Bubble memory is a
non-volatile memory Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typi ...
. Even when power was removed, the bubbles remained, just as the patterns do on the surface of a
disk drive Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...
. 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. Finally, because of the small size of the bubbles, the density was in theory much higher than existing magnetic storage devices. The only downside was performance; the bubbles had to cycle to the far end of the sheet before they could be read.


Commercialization

180px, Bubble memory by MemTech (purchaser of Intel Magnetics). 180px, Bubble memory made in the USSR. Bobeck's team soon had square memories that stored 4,096 bits, the same as a then-standard plane of core memory. This sparked considerable interest in the industry. 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-performance market being the only one they could not serve. The technology was included in experimental devices from Bell Labs in 1974. By the mid-1970s, practically every large electronics company had teams working on bubble memory. Texas Instruments introduced the first commercial product that incorporated bubble memory in 1977. By the late 1970s several products were on the market, and
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 ser ...
released their own 1-megabit version, the 7110. By the early 1980s, however, bubble memory technology became a dead end with the introduction of
hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magn ...
systems offering higher storage densities, higher access speeds, and lower costs. In 1981 major companies working on the technology closed their bubble memory operations. 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. This application became obsolete too with the development of flash storage, which also brought performance, density, and cost benefits. One application was
Konami , is a Japanese multinational video game and entertainment company headquartered in Chūō, Tokyo, it also produces and distributes trading cards, anime, tokusatsu, pachinko machines, slot machines, and arcade cabinets. Konami has ca ...
's Bubble System arcade video game system, introduced in 1984. It featured interchangeable bubble memory cartridges on a 68000-based board. The Bubble System required a "warm-up" time of about 85 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 to operate properly.
Fujitsu is a Japanese multinational information and communications technology equipment and services corporation, established in 1935 and headquartered in Tokyo. Fujitsu is the world's sixth-largest IT services provider by annual revenue, and the la ...
used bubble memory on their FM-8 in 1981 and
Sharp Sharp or SHARP may refer to: Acronyms * SHARP (helmet ratings) (Safety Helmet Assessment and Rating Programme), a British motorcycle helmet safety rating scheme * Self Help Addiction Recovery Program, a charitable organisation founded in 199 ...
used it in their PC 5000 series, a laptop-like portable computer from 1983. Nicolet used bubble memory modules for saving waveforms in their Model 3091 oscilloscope, as did HP who offered a $1595 bubble memory option that extended the memory on their model 3561A digital signal analyzer. GRiD Systems Corporation used it in their early laptops. TIE communication used it in the early development of digital phone systems in order to lower their MTBF rates and produce a non-volatile telephone system's central processor. Bubble memory was also used on the Quantel Mirage DVM8000/1 VFX system.


Further applications

In 2007, the idea of using microfluidic bubbles as
logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or of logical truths. It is a formal science investigating how conclusions follow from prem ...
(rather than memory) was proposed by MIT researchers. The bubble logic would use nanotechnology and has been demonstrated to have access times of 7 ms, which is faster than the 10 ms access times that present hard drives have, though it is slower than the access time of traditional RAM and of traditional logic circuits, making the proposal not commercially practical at present. IBM's 2008 work on racetrack memory is essentially a 1-dimensional version of bubble, bearing an even closer relationship to the original serial twistor concept.


See also

* Gadolinium gallium garnet


References


External links


Great Microprocessors of the Past and Present. Appendix F: Memory Types
Web site by John Bayko
The Arcade Flyer Archive
Konami Bubble System Flyer


Whatever Happened to Bubble Memory?


- Web site by George S. Almasi


Structure of a bubble memory


{{Authority control Computer memory Non-volatile memory