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ABSTRACT
Holographic memory is a technique that can store information at high density
inside crystals. Holographic memory is developing technology that has promised to
revolutionalise the storage systems. Holographic memory offers the possibility of storing
1 terabyte (TB) of data in a sugar-cube-sized crystal. A terabyte of data equals 1,000
gigabytes, 1 million megabytes or 1 trillion bytes. Data from more than 1,000 CDs could
fit on a holographic memory system. Most computer hard drives only hold 10 to 40 GB of
data, a small fraction of what a holographic memory system might hold.
Holographic storage has the potential to become the next generation of storage
media. It has more advantages than conventional storage systems. Conventional
memories use only the surface to store the data. But holographic data storage systems
use the volume to store data. Holographic data storage system (HDSS), a three
dimensional data storage system which enable more information to be stored in a much
smaller space and has a fundamental advantage over conventional read/write memory
systems.
The technology uses holograms which are created when a light from a single laser
beam is split into two beams; the signal beam (which carries the data) and the reference
beam. In holographic storage, at the point where the reference beam and the data
carrying signal beam intersect, the hologram is recorded in the light sensitive storage
medium.
When you create a variance in the reference beam angle or media position then
hundreds of unique holograms can be recorded in the same volume of material. To read
the stored holographic data, the reference beam is deflected off the hologram
reconstructing the stored information. This hologram is then projected onto a detector
that reads the entire data page of over one million bits at once.
After more than 30 years of research and development, a desktop holographic
storage system (HDSS) is close at hand. Early holographic data storage devices will have
capacities of 125 GB and transfer rates of about 40 MB per second. Eventually, these
devices could have storage capacities of 1 TB and data rates of more than 1 GB per
second fast enough to transfer an entire DVD movie in 30 seconds.
Chapter 1
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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, which is
equivalent to about one hour and 15 minutes of music, but Sony has plans to release a
1.3-gigabyte (GB) high-capacity CD. 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.
Mass memory systems serve computer needs in both archival and backup needs.
There exist numerous applications in both the commercial and military sectors that
require data storage with huge capacity, high data rates and fast access. To address such
needs 3-D optical memories have been proposed. Since the data are stored in volume,
they are capable of much higher storage densities than existing 2-D memory systems. In
addition this memory system has the potential for parallel access. Instead of writing or
reading a sequence of bits at each time, entire 2-D data pages can be accessed at one
go.
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.
Storing information through the volume of the medium not on its surface offers
an intriguing high capacity alternative.
Holographic data storage is a volumetric approach, which has made recent
progress towards practicality with the appearance of lower cost enabling technologies.
Hence the holographic memory has become a great white whale of technology research.
Mass memory systems serve computer needs in both archival and backup needs.
There exist numerous applications in both the commercial and military sectors that
require data storage with huge capacity, high data rates and fast access. To address such
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needs 3-D optical memories have been proposed. Since the data are stored in volume,
they are capable of much higher storage densities than existing 2-D memory systems. In
addition this memory system has the potential for parallel access. Instead of writing or
reading a sequence of bits at each time, entire 2-D data pages can be accessed at one
go. With advances in the growth and preparation of various photorefractive materials,
along with the advances in device technologies such as spatial light modulators(SLM),
and detector arrays, the realizations of this optical system is becoming feasible.
A hologram is a recording of the optical interference pattern that forms at the
intersection of two coherent optical beams. Typically, light from a single laser is split into
two paths, the signal path and the reference path.. The beam that propagates along the
signal path carries information, whereas the reference is designed to be simple to
reproduce. A common reference beam is a plane wave: a light beam that propagates
without converging or diverging. The two paths are overlapped on the holographic
medium and the interference pattern between the two beams is recorded. A key
property of this interferometric recording is that when it is illuminated by a readout
beam, the signal beam is reproduced.
Chapter 2
HISTORICAL ROOTS
Dr. Dennis Gabor is known as the father of holography. In year 1947, Dr. Gobor a
Hungerian Physicist given the idea of holography at the imperial college of London
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in1971 Dr. Gabor received a noble prize in physics for holography. His theory was
originally meant to increase the resolving power of electronic microscope and towards
that he used light of beam instead of electronic beam and this resulted in the first
hologram ever made. In 1960s, two engineers from the University of Michigon, Emmitt
Lerth and Juris Upatlipks, developed a new device that produce a 3-D image of an
object. Polaroid scientist Peter J. Vann Heerdern proposed the idea of holographic
storage in the early 1960s and decade later scientist at RCA laboratories demonstrated
the holographic storage technology by recording 500 holograms in an iron doped lithium
niobate crystal and 550 holograms of high resolution images in a light sensitive polymer
material. However, the development of holographic data storage was put on hold for
several years because of the absence of cheap parts of the advancement in magnetic
and semiconductor memories.
In recent years IBM and lucent Bell labs are actively involved in creating a
successful holographic storage medium as a result of which it has become possible to
store 1000 GB of data in a small cube.
After more than 30 years of research and development, a desktop holographic
storage system (HDSS) is close at hand. Early holographic data storage devices will have
capacities of 125 GB and transfer rates of about 40 MB per second. Eventually, these
devices could have storage capacities of 1 TB and data rates of more than 1 GB persecond fast enough to transfer an entire DVD movie in 30 seconds. So why has it taken
so long to develop an HDSS, and what is there left to do?
When the idea of an HDSS was first proposed, the components for constructing
such a device were much larger and more expensive. For example, a laser for such a
system in the 1960s would have been 6 feet long. Now, with the development of
consumer electronics, a laser similar to those used in CD players could be used for the
HDSS. LCDs weren't even developed until 1968, and the first ones were very expensive.
Today, LCDs are much cheaper and more complex than those developed 30 years ago.
Additionally, a CCD sensor wasn't available until the last decade. Almost the entire HDSS
device can now be made from off-the-shelf components, which means that it could be
mass-produced.
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Chapter 3
What is HOLOGRAPHIC STORAGE?
Holographic storage works by storing a sequence of discrete data snapshots
within the thickness of the media. The storage process starts when a laser beam is split
into two signals. One beam is used as a reference signal. Another beam, called the data-
carrying beam, is passed through a device called a spatial light modulator (SLM) which
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acts as a fine shutter system, passing and blocking light at points corresponding to ones
and zeroes. The reference beam is then reflected to impinge on the data-carrying beam
within the media. This creates a three-dimensional refraction pattern (the "hologram")
that is captured in the media. Holographic storage uses circular media similar to a blank
CD or DVD that spins to accept data along a continuous spiral data path. Once the media
is written, data is read back using the reference beam to illuminate the refraction.
This three-dimensional aspect of data recording is an important difference
between holographic storage and conventional CD/DVD recording. Traditional optical
media uses a single laser beam to write data in two dimensions along a continuous spiral
data path. In contrast, prototype holographic storage products save 1 million pixels at a
time in discrete snapshots, also called pages, which form microscopic cones through the
thickness of the light-sensitive media. Today's holographic media can store over 4.4
million individual pages on a disc.
Today, holographic storage is a WORM technology that relies on light-sensitive
media housed in removable protective cartridges. Although rewritable media and drives
will appear in the next few years, much like the progression from CD-R to CD-RW or
from DVD-R to DVD-RW, experts note that the most likely application for WORM media is
for long-term archiving.
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FIG: STORAGE TECHNIQUE
The basic components that are needed to construct an HDSS:
Blue-green argon laser
Beam splitters to spilt the laser beam
Mirrors to direct the laser beams
LCD panel (spatial light modulator)
Lenses to focus the laser beams
Lithium-niobate crystal or photopolymer
Charge-coupled device (CCD) camera
Chapter 4
How are holographic drives specified and deployed?
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Ultimately, any discussion of holographic storage deployment is theoretical
because there are no commercial products available today. Beta products are being
evaluated, but manufacturers, like InPhase Technologies Inc., are keeping their beta
users under wrap. Consequently, there is no word from the field about value,
performance, reliability or any application of holographic products. Still, there are
important trends worth noting.
As with most storage devices, the key issues to consider are capacity and data
transfer rates. Although holographic storage capacity and performance are currently
below current disk and tape systems, they compare favorably to existing optical storage
devices. Today, holographic storage media holds 300 GB (uncompressed), and beta
drives from vendors, like InPhase, are expected to utilize that media. The InPhase
product roadmap touts uncompressed capacities up to 1.6 TB over the next few years.
Holographic drives, such as the fledgling InPhase Tapestry 300r, cite data rates of 160
Mbps. Seek time can be a lengthy 250 milliseconds, and you can expect almost two
seconds to load or unload the disk cartridge.
The SLM is a critical part of the overall drive capacity and performance. SLMs in
today's early drives use a 1,000 x 1,000 pixel matrix (1 million bits) to modulate laser
light and encode each data page. In order to increase storage capacity, SLMs must
eventually become finer (offering more bits) and switch faster. This will fit more and
larger data pages on each disk and allow the drive to write and read more data per
second.Early generation holographic drives appear positioned as single-disk external
products connected to the local area network (LAN) or storage area network (SAN). As
an example, the Tapestry 300r is expected to provide SCSI, 4 Gbps Fibre Channel
optical, Gigabit Ethernet, SAS, and iSCSI Ethernet connectivity options, allowing the
drive to reside on a wide range of LAN/SAN architectures. When used with a server,
holographic storage devices will invariably require device drivers that correspond to the
operating system in use.
Optical storage technologies use lasers for noncontact read/write operations, and
holographic drives should also be maintenance free. This is a substantial advantage over
tape drives, which require frequent cleaning to remove accumulations of magnetic
particles from the read/write heads.
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Chapter 5
WORKING OF HDSS
5.1 RECORDING DATA ON MEDIUM
FIG : HOW DATA IS RECORDED ON A MEDIUM
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When the blue-green argon laser is fired, a beam splitter creates two beams. One
beam, called the object or signal beam, will go straight, bounce off one mirror and travel
through a spatial-light modulator (SLM). An SLM is a liquid crystal display (LCD) that
shows pages of raw binary data as clear and dark boxes. The information from the page
of binary code is carried by the signal beam around to the light-sensitive lithium-niobate
crystal. A second beam, called the reference beam, shoots out the side of the beam
splitter and takes a separate path to the crystal. When the two beams meet, the
interference pattern that is created stores the data carried by the signal beam in a
specific area in the crystal -- the data is stored as a hologram.
5.2 READING DATA FROM HOLOGRAM
FIG: HOW DATA IS READ FROM HOLOGRAM
In order to retrieve and reconstruct the holographic page of data stored in the
crystal, the reference beam is shined into the crystal at exactly the same angle at which
it entered to store that page of data. Each page of data is stored in a different area of
the crystal, based on the angle at which the reference beam strikes it. During
reconstruction, the beam will be diffracted by the crystal to allow the recreation of the
original page that was stored. This reconstructed page is then projected onto the charge-
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coupled device (CCD) camera, which interprets and forwards the digital information to a
computer.
The key component of any holographic data storage system is the angle at which
the second reference beam is fired at the crystal to retrieve a page of data. It must
match the original reference beam angle exactly. A difference of just a thousandth of a
millimeter will result in failure to retrieve that page of data.
An advantage of a holographic memory system is that an entire page of data can
be retrieved quickly and at one time.
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FIG: READING AN OBJECT
5.3 IMPLEMENTATION
A holographic data storage system consists of a recording medium, an optical
recording system, a photo detector array. A beam of coherent light is split into areference beam and a signal beam which are used to record a hologram into the
recording medium. The recording medium is usually a photo refractive crystal.
A hologram is simply the three-dimensional interference pattern of the
intersection of the reference and signal beams are perpendicular to each other. This
interference pattern is imprinted into the crystal as regions of positive and negative
charges. To retrieve the stored hologram, a beam of light that has the same wavelength
and angle of incidence as the reference beam is sent into the crystal and the resulting
diffraction pattern is used to reconstruct the pattern of the signal beam. Many different
holograms may be stored in the same crystal volume by changing the angle of incidence
of reference beam
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FIG: IMPLEMENTATION OF HDD
The most common holographic recording system uses laser light, a beam splitter
to divide the laser light into reference beam and signal beam, various lenses and mirrors
to redirect the light, a photo reactive crystal, and an array of photo detectors around the
crystal to receive the holographic data. To record a hologram, a beam laser light is split
into two beams by a mirror. These two beams then become the reference and signal
beams. The signal beam interacts with an object and the light that is reflected by the
object intersects the reference beam at right angles. The resulting interference patterncontains all the information necessary to recreate the image of the object after suitable
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processing. The interference pattern is recorded on to a photo reactive material and may
be retrieved at a later time by using a beam that is identical to the reference beam. This
is possible because the hologram has the property that if it is illuminated by either of the
beams used to record it, the hologram causes light to be diffracted in the direction of the
second beam that was used to record it, there by recreating the reflected image of the
object if the reference beam was used to illuminate the hologram. So, the reflected must
be transformed into a real image with mirrors and lenses that can be sent to the laser
detector array.
Chapter 6
What is a HOLOGRAM ?
The word Hologram is derived from Greek word Holos meaning Whole and
GRAM meaning Message. A hologram is often described as a 3-D picture.
While a photograph has an actual physical image, a hologram contains
information about size, shape, brightness and contrast of object being recorded .This
information is stored in a very microscopic and complex pattern of interference. The
interference pattern is made possible by the properties of light generated by a LASER.
In order to record the whole pattern, the light used must be highly directional and
must be one of one color. Such light is called coherent. Because the light from a LASER is
one color and leaves the LASER with one wave in perfect one step with all others, it is
perfect for making hologram. When we shine a light on the hologram the information
that is stored as an interference pattern takes the incoming light and re-creates the
original optical wave front that was reflected off the object hence the eyes and brain now
perceives the object as being in front of us once again.
A hologram is a recording of the optical interference pattern that forms at theintersection of two coherent optical beams. Typically, light from a single laser is split into
two paths, the signal path and the reference path.
The beam that propagates along the signal path carries information, whereas the
reference is designed to be simple to reproduce. A common reference beam is a plane
wave: a light beam that propagates without converging or diverging. The two paths are
overlapped on the holographic medium and the interference pattern between the two
beams is recorded.
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A key property of this interferometric recording is that when it is illuminated by a
readout beam, the signal beam is reproduced. In effect, some of the light is diffracted
from the readout beam to reconstruct a weak copy of the signal beam. If the signal
beam was created by reflecting light off a 3D object, then the reconstructed hologram
makes the 3D object appear behind the holographic medium. When the hologram is
recorded in a thin material, the readout beam can differ from the reference beam used
for recording and the scene will still appear.
Chapter 7
MULTIPLEXING
Once one can store a page of bits in a hologram, an interface to a computer can
be made. The problem arises, however, that storing only one page of bits is notbeneficial. Fortunately, the properties of holograms provide a unique solution to this
dilemma. Unlike magnetic storage mechanisms which store data on their surfaces,
holographic memories store information throughout their whole volume. After a page of
data is recorded in the hologram, a small modification to the source beam before it
reenters the hologram will record another page of data in the same volume. This method
of storing multiple pages of data in the hologram is called multiplexing. The thicker the
volume becomes smaller the modifications to the source beam can be.
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Chapter 8
COMPARISION
Major difference between convention recording techniques and holographic
method is the 3-D approach. Traditional optical media uses a single laser beam while in
this technique a single beam is split into two beams.
In conventional methods all the data bits are stored on the surface of a recording
medium but holographic memory will go beneath the surface and use the volume of the
recording medium for storage, instead of only the surface area.
StorageMedium
Access Time DataTransferRate
StorageCapacity
HolographicMemory
2.4 s 10 GB/s 400 Mbits/cm2
Main Memory(RAM)
10 40 ns 5 MB/s 4.0 Mbits/cm2
Magnetic Disk 8.3 ms 5 20 MB/s 100 Mbits/cm2
Chapter 9
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9.1 ADVANTAGES
With three-dimensional recording and parallel data readout, holographic
memories can outperform existing optical storage techniques. In contrast to the
currently available storage strategies, holographic mass memory simultaneously offers
high data capacity and short data access time (Storage capacity of about 1TB/cc and
data transfer rate of 1 billion bits/second).
Holographic data storage has the unique ability to locate similar features stored
within a crystal instantly. A data pattern projected into a crystal from the top searches
thousands of stored holograms in parallel. The holograms diffract the incoming light out
of the side of the crystal, with the brightest outgoing beams identifying the address of
the data that most closely resemble the input pattern. This parallel search capability is
an inherent property of holographic data storage and allows a database to be searched
by content.
Because the interference patterns are spread uniformly throughout the material,
it endows holographic storage with another useful capability: high reliability. While a
defect in the medium for disk or tape storage might garble critical data, a defect in a
holographic medium doesn't wipe out information. Instead, it only makes the hologram
dimmer.
No rotation of medium is required as in the case of other storage devices. It can
reduce threat of piracy since holograms cant be easily replicated.
9.2 DISADVANTAGES
Manufacturing cost HDSS is very high and there is a lack of availability of
resources which are needed to produce HDSS. However, all the holograms appear
dimmer because their patterns must share the material's finite dynamic range. In other
words, the additional holograms alter a material that can support only a fixed amount of
change. Ultimately, the images become so dim that noise creeps into the read-out
operation, thus limiting the material's storage capacity.
A difficulty with the HDSS technology had been the destructive readout. The re-
illuminated reference beam used to retrieve the recorded information, also excites the
donor electrons and disturbs the equilibrium of the space charge field in a manner that
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produces a gradual erasure of the recording. In the past, this has limited the number of
reads that can be made before the signal-to -noise ratio becomes too low. Moreover,
writes in the same fashion can degrade previous writes in the same region of the
medium. This restricts the ability to use the three-dimensional capacity of a
photorefractive for recording angle-multiplexed holograms. You would be unable to
locate the data if theres an error of even a thousandth of an inch.
Chapter 10
APPLICATIONS
There are many possible applications of holographic memory. Holographic
memory systems can potentially provide the high speed transfers and large volumes of
future computer system. One possible application is data mining. Data mining is the
processes of finding patterns in large amounts of data. Data mining is used greatly in
large databases which hold possible patterns which cant be distinguished by human
eyes due to the vast amount of data. Some current computer system implement data
mining, but the mass amount of storage required is pushing the limits of current data
storage systems. The many advances in access times and data storage capacity that
holographic memory provides could exceed conventional storage and speedup data
mining considerably. This would result in more located patterns in a shorter amount of
time.
Another possible application of holographic memory is in petaflop computing. A
petaflop is a thousand trillion floating point operations per second. The fast access
extremely large amounts of data provided by holographic memory could be utilized in
petaflop architecture. Clearly advances are needed to in more than memory systems,
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but the theoretical schematics do exist for such a machine. Optical storage such as
holographic memory provides a viable solution to the extreme amount of data which is
required for a petaflop computing.
The three main companies involved in developing holographic memory, as of
2002, were InPhase and Polaroid spinoff Aprilis in the United States, and Optware in
Japan. Although holographic memory has been discussed since the 1960s, and has been
touted for near-term commercial application at least since 2001, it has yet to convince
critics that it can find a viable market. As of 2002, planned holographic products did not
aim to compete head to head with hard drives, but instead to find a market niche based
on virtues such as speed of access.
Inphase Technologies, after several announcements and subsequent delays in
2006 and 2007, announced that it would soon be introducing a flagship product. InPhase
went out of business in February 2010 and had its assets seized by the state of Colorado
for back taxes. The company had reportedly gone through $100 million but the lead
investor was unable to raise more capital.
In April 2009, GE Global Research demonstrated their own holographic storage
material that could allow for discs that utilize similar read mechanisms as those found on
Blu-ray Disc players.
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Chapter 11
FUTURE SCOPE
The future of holographic storage is fraught with unknowns. "This technology is
very promising. I've been hearing about it for years," Garrett says. "But at this point, the
No. 1 concerns are [high] cost and [product] immaturity." Experts agree that capacity
and performance will only increase over time, moving from 300 GB to 800 GB and finally
on to 1.6 TB over the next 48 months or so. But the pace of improvements will
ultimately rest heavily on industry acceptance. Given that holographic technology is
currently geared toward a niche in the storage market, it may be years before early
product releases give way to more capable and cost-effective systems that appeal to a
larger storage audience.
Experts also note the possible introduction of "hybrid" holographic media. Just as
magnetic hard drives are starting to incorporate significant quantities of flash or RAM
within the disk, near-term holographic storage media may add some amount of flash
memory in the cartridge to provide a degree of rewritability until a suitable rewritable
media is developed and productized.
Backward compatibility also remains a significant unknown. No tape drive in your
enterprise today is capable of reading a tape written 50 years ago, and the same specter
is in the cards for holographic storage. For example, the InPhase product roadmap
suggests a third generation of holographic drives in roughly four years and promises
backward compatibility with the previous two generations. (Back to first generation in
this case.) Well, then what? If the fifth or sixth or 10th generation drives cannot read the
holographic disks written today, you'll need to either retain the older drive software and
hardware, assuming that it still functions, or rewrite the older disks to the newer media
later -- defeating the purpose of such long retention. "The same corner case that
justifies holographic storage also works against it," Schulz says.
Researchers are confident that technologies will be developed in the next two or
three years to meet these challenges. This DVD-like disc would have a capacity 27 times
greater than the 4.7-GB DVDs available today, and the playing device would have data
rates 25 times faster than today's fastest DVD players.
Chapter 12
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CONCLUSION
The future of HOLOGRAPHIC DATA STORAGE SYSYEM is very promising. The page
access of data that HDSS 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 HDSS impractical. It will most likely be
used in next generation supercomputers 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 system 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 operateson the same principles used in the first magnetic data storage devices. The parallel
nature of HDSS 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 our computer systems.
BIBLIOGRAPHY
.......www.holopc.com
........www.wikeipedia.com
..........www.computer.howstuffworks.com
http://www.engineeringproject.net/seminars/holographic_memory/SUPER%20COMPUTER.htmhttp://www.engineeringproject.net/seminars/holographic_memory/SUPER%20COMPUTER.htm