Bubble memory

The invention: An early nonvolatile medium for storing information
on computers.
The person behind the invention:
Andrew H. Bobeck (1926- ), a Bell Telephone Laboratories
scientist
Magnetic Technology
The fanfare over the commercial prospects of magnetic bubbles
was begun on August 8, 1969, by a report appearing in both The New
York Times and TheWall Street Journal. The early 1970’s would see the
anticipation mount (at least in the computer world) with each prediction
of the benefits of this revolution in information storage technology.
Although it was not disclosed to the public until August of 1969,
magnetic bubble technology had held the interest of a small group
of researchers around the world for many years. The organization
that probably can claim the greatest research advances with respect
to computer applications of magnetic bubbles is Bell Telephone
Laboratories (later part of American Telephone and Telegraph). Basic
research into the properties of certain ferrimagnetic materials
started at Bell Laboratories shortly after the end of World War II
(1939-1945).
Ferrimagnetic substances are typically magnetic iron oxides. Research
into the properties of these and related compounds accelerated
after the discovery of ferrimagnetic garnets in 1956 (these are a
class of ferrimagnetic oxide materials that have the crystal structure
of garnet). Ferrimagnetism is similar to ferromagnetism, the phenomenon
that accounts for the strong attraction of one magnetized
body for another. The ferromagnetic materials most suited for bubble
memories contain, in addition to iron, the element yttrium or a
metal from the rare earth series.
It was a fruitful collaboration between scientist and engineer,
between pure and applied science, that produced this promising breakthrough in data storage technology. In 1966, Bell Laboratories
scientist Andrew H. Bobeck and his coworkers were the first to realize
the data storage potential offered by the strange behavior of thin
slices of magnetic iron oxides under an applied magnetic field. The
first U.S. patent for a memory device using magnetic bubbles was
filed by Bobeck in the fall of 1966 and issued on August 5, 1969.
Bubbles Full of Memories
The three basic functional elements of a computer are the central
processing unit, the input/output unit, and memory. Most implementations
of semiconductor memory require a constant power
source to retain the stored data. If the power is turned off, all stored
data are lost. Memory with this characteristic is called “volatile.”
Disks and tapes, which are typically used for secondary memory,
are “nonvolatile.” Nonvolatile memory relies on the orientation of
magnetic domains, rather than on electrical currents, to sustain its
existence.
One can visualize by analogy how this will work by taking a
group of permanent bar magnets that are labeled withNfor north at
one end and S for south at the other. If an arrow is painted starting
from the north end with the tip at the south end on each magnet, an
orientation can then be assigned to a magnetic domain (here one
whole bar magnet). Data are “stored” with these bar magnets by arranging
them in rows, some pointing up, some pointing down. Different
arrangements translate to different data. In the binary world
of the computer, all information is represented by two states. A
stored data item (known as a “bit,” or binary digit) is either on or off,
up or down, true or false, depending on the physical representation.
The “on” state is commonly labeled with the number 1 and the “off”
state with the number 0. This is the principle behind magnetic disk
and tape data storage.
Now imagine a thin slice of a certain type of magnetic material in
the shape of a 3-by-5-inch index card. Under a microscope, using a
special source of light, one can see through this thin slice in many regions
of the surface. Darker, snakelike regions can also be seen, representing
domains of an opposite orientation (polarity) to the transparent
regions. If a weak external magnetic field is then applied by placing a permanent magnet of the same shape as the card on the
underside of the slice, a strange thing happens to the dark serpentine
pattern—the long domains shrink and eventually contract into
“bubbles,” tiny magnetized spots. Viewed from the side of the slice,
the bubbles are cylindrically shaped domains having a polarity opposite
to that of the material on which they rest. The presence or absence
of a bubble indicates either a 0 or a 1 bit. Data bits are stored by
moving the bubbles in the thin film. As long as the field is applied
by the permanent magnet substrate, the data will be retained. The
bubble is thus a nonvolatile medium for data storage.Consequences
Magnetic bubble memory created quite a stir in 1969 with its
splashy public introduction. Most of the manufacturers of computer
chips immediately instituted bubble memory development projects.
Texas Instruments, Philips, Hitachi, Motorola, Fujitsu, and International
Business Machines (IBM) joined the race with Bell Laboratories
to mass-produce bubble memory chips. Texas Instruments
became the first major chip manufacturer to mass-produce bubble
memories in the mid-to-late 1970’s. By 1990, however, almost all the
research into magnetic bubble technology had shifted to Japan.
Hitachi and Fujitsu began to invest heavily in this area.
Mass production proved to be the most difficult task. Although
the materials it uses are different, the process of producing magnetic
bubble memory chips is similar to the process applied in producing
semiconductor-based chips such as those used for random access
memory (RAM). It is for this reason that major semiconductor manufacturers
and computer companies initially invested in this technology.
Lower fabrication yields and reliability issues plagued
early production runs, however, and, although these problems
have mostly been solved, gains in the performance characteristics of
competing conventional memories have limited the impact that
magnetic bubble technology has had on the marketplace. The materials
used for magnetic bubble memories are costlier and possess
more complicated structures than those used for semiconductor or
disk memory.
Speed and cost of materials are not the only bases for comparison. It is possible to perform some elementary logic with magnetic
bubbles. Conventional semiconductor-based memory offers storage
only. The capability of performing logic with magnetic bubbles
puts bubble technology far ahead of other magnetic technologies
with respect to functional versatility.
Asmall niche market for bubble memory developed in the 1980’s.
Magnetic bubble memory can be found in intelligent terminals, desktop
computers, embedded systems, test equipment, and similar microcomputer-
based systems.