INTRODUCTION
Devices that use light to store and read data have been the backbone of data storage for nearly two decades. Compact discs revolutionized data storage in the early 1980s, allowing multi-megabytes of data to be stored on a disc that has a diameter of a mere 12 centimeters and a thickness of about 1.2 millimeters. In 1997, an improved version of the CD, called a digital versatile disc (DVD), was released, which enabled the storage of full-length movies on a single disc.
CDs and DVDs
are the primary data storage methods for music, software, personal computing
and video. A CD can hold 783 megabytes of data. A double-sided, double-layer
DVD can hold 15.9 GB of data, which is about eight hours of movies. These
conventional storage mediums meet today's storage needs, but storage
technologies have to evolve to keep pace with increasing consumer demand. CDs,
DVDs and magnetic storage all store bits of information on the surface of a
recording medium. In order to increase storage capabilities, scientists are now
working on a new optical storage method called holographic memory that will go beneath the surface and use the
volume of the recording medium for
storage, instead of only the surface area.
Three-dimensional data storage will be able to store more information in a
smaller space and offer faster data transfer times.
HOLOGRAPHY
A hologram is a
block or sheet of photosensitive material which records the interference of two
light sources. To create a hologram,
laser light is
first split into
two beams, a
source beam and a
reference beam. The source beam is then
manipulated and sent into the photosensitive material. Once
inside this material,
it intersects the reference beam and the resulting interference of laser
light is
recorded on the
photosensitive material, resulting
in a hologram. Once a hologram is recorded, it can be
viewed with only the reference beam. The
reference beam is projected into the hologram at the exact angle it was
projected during recording. When this
light hits the
recorded diffraction pattern,
the source beam is regenerated out of the refracted light. An exact copy of the source
beam is sent
out of the hologram
and can be read by optical sensors.
For example, a
hologram that can
be obtained from a
toy store illustrates
this idea. Precise laser equipment is used at the
factory to create the hologram. A
recording material which can recreate recorded images out of natural light is
used so the consumer does
not need high-tech
equipment to view
the information stored in
the hologram. Natural light becomes the reference beam
and human eyes become the optical sensors.
Holography was invented in 1947 by the Hungarian-British physicist
Dennis Gabor (1900-1979), who won a 1971 Nobel Prize for his invention.
CONCLUSION
The future of
holographic memory is very promising.
The page access of data
that holographic memory creates
will provide a window into next
generation computing by
adding another dimension to
stored data. Finding holograms in personal computers
might be a bit longer off, however. The
large cost of high-tech optical equipment would make small-scale systems
implemented with holographic memory impractical.
Holographic memory will
most likely be
used in next
generation super computers where
cost is not as much of an
issue. Current magnetic storage
devices remain far more cost effective than any other medium on the
market. As computer systems evolve, it
is not unreasonable
to believe that magnetic storage will continue to do
so. As mentioned earlier, however,
these improvements are not made on the conceptual level. The current storage in a personal computer
operates on the same principles used in the first magnetic data storage
devices. The parallel nature of
holographic memory has many potential gains on serial storage methods. However,
many advances in
optical technology and photosensitive materials
need to be
made before we
find holograms in computer systems.
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