Bubble memory
Encyclopedia
Bubble memory is a type of non-volatile
Non-volatile memory
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
computer memory
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each storing one bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
of data. Bubble memory started out as a promising technology in the 1970s, but failed commercially as hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
performance and cost improvements in the 1980s overtook its advantages.
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 memoryMagnetic core memory
Magnetic-core memory was the predominant form of random-access computer memory for 20 years . It uses tiny magnetic toroids , the cores, through which wires are threaded to write and read information. Each core represents one bit of information...
system driven by a transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
-based controller, and the second was the development of twistor memory
Twistor memory
Twistor is a form of computer memory, similar to core memory, formed by wrapping or closing magnetic tape around a current-carrying wire. Although the developers, Bell Labs, had high hopes for Twistor, it was used for only a brief time in the marketplace between about 1968 and the mid-1970s...
.
Twistor memory
Twistor memory
Twistor is a form of computer memory, similar to core memory, formed by wrapping or closing magnetic tape around a current-carrying wire. Although the developers, Bell Labs, had high hopes for Twistor, it was used for only a brief time in the marketplace between about 1968 and the mid-1970s...
was based on magnetostriction
Magnetostriction
Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of material's magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ...
, an effect that can be used to move magnetic bits. If a pattern is placed on a medium (for instance, magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
) and then a current is passed through the tape, the patterns will slowly be "pushed" down the tape while the patterns themselves will remain unchanged. By placing a detector at some point over the tape, the fields will pass under it in turn without any physical motion. In effect it is a solid state
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
version of a single track from a drum memory
Drum memory
Drum memory is a magnetic data storage device and was an early form of computer memory widely used in the 1950s and into the 1960s, invented by Gustav Tauschek in 1932 in Austria....
. In the 1960s, AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
had used Twistor in a number of applications.
Magnetic bubbles
In 1967, Bobeck joined a team at Bell LabsBell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
and started work on improving Twistor. He thought that, if he could find a material that allowed the movement of the fields easily in only one direction, a strip of such material could have a number of read/write heads positioned along its edge instead of only one. Patterns would be introduced at one edge of the material and pushed along just as in Twistor, but since they could be moved in one direction only, they would naturally form "tracks" across the surface, increasing the areal density
Computer storage density
Memory storage density is a measure of the quantity of information bits that can be stored on a given length of track, area of surface, or in a given volume of a computer storage medium. Generally, higher density is more desirable, for it allows greater volumes of data to be stored in the same...
. This would produce a sort of "2D Twistor".
Paul Charles Michaelis
Paul Charles Michaelis
Paul Charles Michaelis was a Bell Labs researcher in magnetic bubble memory.-Education:Michaelis was born June 18, 1935, received BSEE and MS Physics from Newark College of Engineering .-Career:...
working with Permalloy magnetic thin films discovered that it was possible to propagate magnetic domains 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, September 15, 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.
Starting work extending this concept using orthoferrite
Orthoferrite
An orthoferrite is any of a class of chemical compounds with the formula RFeO . Orthoferrites have an orthorhombic crystal structure with a space group Pbnm and most are weakly ferromagnetic....
, 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 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 A.H.Bobeck working at Bell Labs in New Jersey, were awarded the IEEE Morris N. Liebmann Memorial Award
IEEE Morris N. Liebmann Memorial Award
The initially called Morris Liebmann Memorial Prize provided by the Institute of Radio Engineers , 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 had "made public during the recent past an important...
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 they discovered that garnet
Garnet
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
turned out to have the right 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
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
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
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
. Even when power was removed, the bubbles remained, just as the patterns do on the surface of a disk drive. 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
Bobeck's team soon had 1 cm 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.
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
systems. Almost all work on it stopped.
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 memory
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
, which also brought performance, density, and cost benefits.
One application was Konami
Konami
is a Japanese leading developer and publisher of numerous popular and strong-selling toys, trading cards, anime, tokusatsu, slot machines, arcade cabinets and video games...
's Bubble System
Bubble System
The Bubble System is an arcade system board designed by Konami and used across many arcade games in the early eighties.The Bubble System was supposed to have a unique new form of data storage for arcade-style video games. It used bubble memory cartridges, a sort of non-mechanical magnetic storage...
arcade video game system, introduced in 1984. It featured interchangeable bubble memory cartridges on a 68000
Motorola 68000
The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...
-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. Sharp
Sharp Corporation
is a Japanese multinational corporation that designs and manufactures electronic products. Headquartered in Abeno-ku, Osaka, Japan, Sharp employs more than 55,580 people worldwide as of June 2011. The company was founded in September 1912 and takes its name from one of its founder's first...
used bubble memory in their PC 5000
Sharp PC-5000
The Sharp PC-5000 was a pioneering laptop computer, announced by Sharp Corporation of Japan in 1983. Like the GRiD Compass, which preceded it, and its contemporary the Gavilan SC, it employed a clamshell design in which the display closes over the keyboard....
series, a laptop-like portable computer from 1983. Nicolet used bubble memory modules for saving waveforms in their Model 3091 oscilloscope. GRiD Systems Corporation
GRiD Systems Corporation
GRiD Systems Corporation was founded in January, 1979 by John Ellenby, who left his job at Xerox Parc and joined Glenn Edens, Dave Paulsen and Bill Moggridge to form one of Silicon Valley's first stealth companies...
used it in their early laptops.
Further applications
In 2007, the idea of using microfluidic bubbles as logicFluidics
Fluidics or Fluidic logic is the use of a fluid to perform analog or digital operations similar to those performed with electronics.The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dynamics...
(rather than memory) was proposed by MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
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.
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
- Bubbles: the better memory
- Whatever Happened to Bubble Memory?
- Magnetic Bubble Memories - Web site by George S. Almasi