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ABSTRACT
Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which would greatly increase storage over Blue-ray Disc and HP DVD optical disc systems. It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used as the reference beam and to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed amongst the data.
A dichroic mirror layer between the holographic data and the servo data reflects the blue-green laser while letting the red laser pass through. This prevents interference from refraction of the blue-green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology.These discs have the capacity to hold up to 3.9 terabyte(TB) of information, which is approximately 6,000 times the capacity of a CD-ROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray Discs, and about 8 times the capacity of standard computer hard drives as of 2006. The HVD also has a transfer rate of 1 gigabit/s. Optware is expected to release a 200 GB disc in early June 2006, and Maxell in September 2006 with a capacity of 300 GB and transfer rate of 20 MB/s.
1. INTRODUCTION
Requirements for removable media storage devices (RMSDs) used with personal computers have changed significantly since the introduction of the floppy disk in 1971. At one time, desktop computers depended on floppy disks for all of their storage requirements. Even with the advent of multi Gigabyte hard drives and fast Internet connections, floppy disks and other RMSDs are still an integral part of most computer systems, providing:
t* Transport between computers for data files and software
Backup to preserve data from the hard disks.
A way to load the operating system software in the event of a hard-drive failure.
Some RMSD options available today are approaching the performance, capacity, and cost of hard-disk drives. Considerations for selecting an RMSD include capacity, speed, convenience, durability, data availability, and backward compatibility. Technology options used to read and write data include:
Magnetic formats that use magnetic particles and magnetic fields. > Optical formats that use laser light and optical sensors.
Magneto-optical and magneto-optical hybrids that use a combination of magnetic and optical properties to increase storage capacity.
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2. REMOVABLE MEDIA STORAGE DEVICES (RMSDs)
Let us have a glance on the different RMSDs.
2.1 Floppy Disk
Floppy disk drives provide faster data access because they access data randomly. Floppy drives provide an average data access speed of less than 100 milliseconds (ms).
The 1.44-MB, 3.5-inch floppy is useful for storing and backing up small data files, can be used to boot computer systems, and has been the standard for data interchange between PCs. However it provides only a fraction of the storage capacity required for many files and most software programs in use today. Storing data on floppy drives also is slow. Data transfer rates average around 0.06 MB/sec.
2.2 Optical Formats
Optical RMSD formats use a laser light source to read and/or write digital data to disc. CD and DVD are two major optical formats. CDs and DVDs have similar compositions consisting of a label, a protective layer, a reflective layer (aluminum, silver, or gold), a digital-data layer molded in polycarbonate, and a thick polycarbonate bottom layer
Label layer
Reflective layer
Digital-data layer
Bottom Of disc Polycarbonate
layer
Optical Disk Composition
CD formats include:
¦ Compact disc-read only memory (CD-ROM)
¦ Compact disc-recordable (CD-R)
¦ Compact disc-rewritable (CD-RW)
DVD formats include:
¦ Digital versatile disc-read only memory (DVD-ROM)
¦ Digital versatile disc-recordable (DVD-R) DVD-RAM (rewritable)
¦ Digital versatile disc-rewritable (DVD-RW)
¦ +RW (rewritable)
2.3 CD-ROM
CD-ROM Standard was established in 1984.They quickly evolved into a low cost digital storage option because of CD-audio industry
Data bits are permanently stored on a CD as a spiral track of physically molded pits in the surface of a plastic data layer that is coated with reflective aluminum. Smooth areas surrounding pits are called lands. CDs are extremely durable because the optical pickup (laser light source, lenses and optical elements, photoelectric sensors, and amplifiers) never touches the disc. Because data is read through the thick bottom layer, most scratches and dust on the disc surface are out of focus, so they do not interfere with the reading process.
One CD-ROM (650-700 MB) storage capacity can store data from more than 450 floppy disks. Data access rate ranges from 80 to 120 ms. Data transfer rates are approximately 6 MB/sec.
2.4 DVD-ROM
The DVD-ROM standard, introduced in 1995 came over as a result of a DVD consortium. Like CD drives, DVD drives read data through the disc substrate reducing interferences from surface dust and scratches. However DVD-ROM technology provides seven times the storage capacity of CDs and accomplishes most of this increase by advancing the technology used for CD systems. The distance between recording tracks is les than half that is used for CDs. The pit size also is less than half
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that of CDs, which requires a reduced laser wavelength read the smaller sized pits. These features alone give DVD-ROM discs 4.5 times the storage capacity of CDs.
DVD drives can also store on both sides of the disc; manufacturers deliver the two-sided structure by bonding two thinner substrates together, providing the potential to double a DVD's storage capacity. Single sided DVD discs have the two fused substrates, but only one side contains data.
In a DVD, storage of data in the data layers can be:
Single-sided, single layer (4.7 GB)
Double-sided, single layer (9.4 GB)
Single-sided, double layer (8.5 GB)
Double-sided, double layer (17 GB)
Single-sided, single layer (4.7GB) Single-sided, double layer (8.5 GB)
0.6mm
0.6mm
Double-sided. Single layer (9.4 GB)
Double.-sided, double layer (1" GB)
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Figure: DVD Data Storage Versions
2.5 DVD-R
DVD-R drives were introduced in 1997 to provide write-once capability on DVD-R discs used for producing disc masters in software development and for multimedia post-production. This technology sometimes referred to as DVD-R for authoring, is limited to niche applications because drives and media are expensive.
DVD-R discs employ a photosensitive dye technology similar to CD-R media. At 3.95 GB per side, the first DVD-R discs provided a little less storage capacity than DVD-ROM discs. That capacity has now been extended to the 4.7-GB capacity of DVD-ROM discs. The IX DVD-R data transfer rate is 1.3 MB/sec. Most DVD-ROM drives and DVD video players read DVD-R discs. Slightly modified DVD-R drives and discs have recently become available for general use.
2.6 DVD-RAM
DVD-RAM (rewritable) drives were introduced in 1998. DVD-RAM devices use a phase change technology combined with some embossed land/pit features. Employing a format termed "land groove", data is recorded in the grooves formed on the disc and on the land between the grooves. The initial disc capacity was
2.6 GB per side, but a 4.7 GB- per-side version is now available.
The 4.7-GB DVD-RAM discs come in cartridges that protect the medium from handling damage, such as fingerprints and scratches. A single-sided disc is expected to be removable from the cartridge so it can also be played in DVD-ROM drives that support DVD-RAM. The double-sided disc, providing 4.7GB of storage capacity per side, is not removable from the cartridge.
Each DVD-RAM disc is reported to handle more than 100,000 rewrites. DVD-RAM is specifically designed for PC data storage; DVD-RAM discs use a storage structure based in sectors, instead of the spiral groove structure used for CD data storage. This sector storage is similar to the storage structure used by hard drives. Sector storage results in faster random data access speed.
Because of their high cost relative to CD-RW technology, current consumer-oriented DVD-RAM drives and media are not a popular choice for PC applications. Slow adoption of DVD-RAM reading capability in DVD-ROM drives has also limited DVD-RAM market acceptance.
2.7 DVD-RW
The DVD-RW drive format is similar to the DVD-R format, but offers rewritability using a phase-change recording layer that is comparable to the phase-change layer used for CD-RW. DVD-RW is intended for consumer video (non -PC) use, but PC applications are also expected for this technology. The first DVD-RW drives based on this format, which also recorded DVD-R discs, were introduced in early 2001.
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2.8 +RW
Sony and Philips were founding members of the DVD consortium, but broke away to introduce the DVD+RW (now called +RW) phase change, rewritable technology in 1997. Discs can be written approximately 1000 times, which makes them a good option for video recording, but not optimal for data storage. +RW technology's strongest feature is its backward compatibility with DVD-ROM drives and DVD video players.
2.9 Magneto-Optical Formats
Magneto-optical (MO) technology combines he strengths of magnetic and optical technologies by using a laser to read data and the combination of a laser and magnetic field to write data. The top (label side) of the disk is exposed to a magnetic field to write data, and a laser light source targets the data layer through the bottom substrate to read data.
There are 3.5- and 5.5-inch disk formats that contain a magnetic alloy layer. Magnetic particles in the alloy are very stable and resist changing polarity at room temperature. Data bits re recorded on this magnetic layer by heating it with a focused laser beam in the presence of magnetic field. Changes in the magnetic orientation of the data bits along a track represents 0s and 1 s much like on hard disks and other magnetic media. The magnetic layer also changes the rotation or polarization of reflected laser light depending on the 0 or 1 polarity of the magnetic bits. This property called the "Kerr Effect" and is used to read the data. MO systems also increase the data bits vertically rather than horizontally.
The 3.5-inch disks are available in 128-, 230-, and 640-MB storage capacities. The 5.25-inch disks come in 650-MB and 1.3-, 2.6-, and 5.2-GB sizes. A 9.1 -GB size is expected soon. At less than 25ms, data access times faster than the average 100ms of phase change CD and DVD technologies. MO drives are widely used in Japan for general-purpose storage, similar to the way Zip drives are used in the U.S. Outside of Japan; applications for MO drives typically have been in niche markets for Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM), document imaging, and high-capacity archives.
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Holographic Versatile Disc 3. HOLOGRAPHIC VERSATILE DISC
3.1How Holographic Versatile Discs Work
Holographic memory systems have been around for decades. They offer tar more storage capacity than CDs and DVDs †even "next-generation" DVDs like Blu-ray †and their transfer rates leave conventional discs in the dust. So why haven't we all been using holographic memory for years now
There are several hurdles that have been holding Holographic versatile disc holographic storage back from the realm of mass
consumption, including price and complexity. Until now, the systems have required a cost-prohibitive level of precision in manufacturing. But recent changes have made the holographic versatile disc (HVD) developed by Optware a viable option for consumers.
In this article, we'll find out how the HVD works, how it has improved upon previous methods of holographic storage and how it stacks up to Blu-ray and HD-DVD
3.2Basics of Holographic Memory
The first step in understanding holographic memory is to understand what "holographic" means. Holography is a method of recording patterns of light to produce a three-dimensional object. The recorded patterns of light are called a hologram.
The process of creating a hologram begins with a focused beam of light ~ a laser beam. This laser beam is split into two separate beams: a reference beam, which remains unchanged throughout much of the process, and an information beam, which passes 3-D image of the Death Star through an image. When light encounters an image, its created by holography composition changes (see How Light Works to learn
about this process). In a sense, once the information beam encounters an image, it carries that image in its waveforms. When these two beams intersect, it creates a pattern of light interference. If you record this pattern of light interference †for example, in a photosensitive polymer layer of a disc - you are essentially recording the light pattern of the image.
To retrieve the information stored in a hologram, you shine the reference beam directly onto the hologram. When it reflects off the hologram, it holds the light pattern of the image stored there. You then send this reconstruction beam to a CMOS sensor to recreate the original image.
Most of us think of holograms as storing the image of an object, like the Death Star pictured above. The holographic memory systems we're discussing here use holograms to store digital instead of analog information, but it's the same concept. Instead of the information beam encountering a pattern of light that represents the
Death Star, it encounters a pattern of light and dark areas that represent ones and zeroes.
Encoded page data
HVD offers several advantages over traditional storage technology. HVDs can ultimately store more than 1 terabyte (TB) of information †that's 200 times more than a single-sided DVD and 20 times more than a current double-sided Blu-ray. This is partly due to HVDs storing holograms in overlapping patterns, while a DVD basically stores bits of information side-by-side. HVDs also use a thicker recording layer than DVDs †an HVD stores information in almost the entire volume of the disc, instead of just a single, thin layer.
The other major boost over conventional memory systems is HVD's transfer rate of up to 1 gigabyte (GB) per second - that's 40 times faster than DVD. An HVD stores and retrieves an entire page of data, approximately 60,000 bits of information, in one pulse of light, while a DVD stores and retrieves one bit of data in one pulse of light.
Now that we know the premise at work in HVD technology, let's take a look at the structure of the Optware disc.
3.3The Holographic Data storage Basics
Prototypes developed by Lucent and IBM differ slightly, but most holographic data storage systems (HDSS) are based on the same concept. Here are 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
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. Some systems use a photopolymer in place of the 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.
An advantage of a holographic memory system is that an entire page of data can be retrieved quickly and at one time. 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-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.
3.4The Holographic Versatile Disc
Holographic memory has been around for more than 40 years, but several characteristics made it difficult to implement in a consumer market. First off, most of these systems send the reference beam and the information beam into the recording medium on different axes. This requires highly complex optical systems to line them up at the exact point at which they need to intersect. Another drawback has to do with incompatibility with current storage media: Traditionally, holographic storage systems contained no servo data, because the beam carrying it could interfere with the holography process. Also, previous holographic memory discs have been notably thicker than CDs and DVDs.
Optware has implemented some changes in its HVD that could make it a better fit for the consumer market. In the HVD system, the laser beams travel in the same axis and strike the recording medium at the same angle, which Optware calls the collinear method. According to Optware, this method requires a less complex system of optics, enabling a smaller optical pickup that is more suited to consumer use.
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HVD optical pickup
HVD also includes servo data. The servo beam in the HVD system is at a wavelength that does not photosensitize the polymer recording medium. In the HVD test system, the servo data is carried in a red (650-nm wavelength) laser. The size and thickness of an HVD is also compatible with CDs and DVDs.
The structure of the disc places a thick recording layer between two substrates and incorporates a dichroic mirror that reflects the blue-green light carrying the holography data but allows the red light to pass through in order to gather servo information.
4.STATUS OF DEVELOPMENT
4.1 Holographic Versatile Disc structure
Disc Structure
Green or
1. Green writing/reading laser (532nm)
2. Red positioning/addressing laser (650nm)
3. Hologram (data)
4. Polycarbon layer
5. Photopolymeric layer (data-containing layer)
6. Distance layers
7. Dichroic layer (reflecting green light)
8. Aluminium reflective layer (reflecting red light)
9. Transparent base
Diagonistic layer
A dichroic filter is a very-accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, Dichroic mirrors and dichroic reflectors tend to be characterized by the color(s) of light that they reflect rather than the color(s) they pass. (See dichroic for the etymology of the term.)
Used in front of a light source, a dichroic filter produces light that is perceived by humans to be highly saturated (intense) in color. Although costly, such filters are popular in architectural and theatrical applications.
Used behind a light source, dichroic reflectors commonly reflect visible light forward while allowing the invisible infrared light (radiated heat) to pass out of the rear of the fixture, resulting in a beam of light that is "cooler". Modern quartz halogen incandescent light bulbs frequently contain an integrated dichroic reflector (see picture).
A dichroic filter is a very-accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, Dichroic mirrors and dichroic reflectors tend to be characterized by the color(s) of light that they reflect rather than the color(s) they pass. (See dichroic for the etymology of the term.)
Used in front of a light source, a dichroic filter produces light that is perceived by humans to be highly saturated (intense) in color. Although costly, such filters are popular in architectural and theatrical applications.
Dichroic filters operate using the principle of interference. Alternating layers of an optical coating are built up upon a glass substrate, selectively reinforcing certain wavelengths of light and interfering with other wavelengths. The layers are usually deposited using a process carried out in a vacuum. By controlling the thickness and number of the layers, the frequency (wavelength) of the passband of the filter can be tuned and made as wide or narrow as desired. Because unwanted wavelengths are reflected rather than absorbed, dichroic filters don't absorb much energy during operation and so don't become nearly as hot as the equivalent conventional filter (which attempts to absorb all energy except for that in the passband).
Filter
An optical filter is a device which selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light, or polarizations), while blocking the remainder. They are commonly used in photography, in many optical instruments, and to colour stage lighting-Optical coating
An optical coating is a thin layer of material placed on an optical component such as a lens or mirror which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and is commonly used on spectacle and photographic lenses. Another type is the high-reflector coating which can be used to produce mirrors which reflect greater than 99% of the light which falls on them. More complex optical coatings exhibit high-reflection over some range of wavelengths, and anti-reflection over another range, allowing the production of dichroic thin-film optical filters.
Passband
In telecommunications, optics, and acoustics, passband is the portion of spectrum, between limiting frequencies that is transmitted with minimum relative loss or maximum relative gain by a filtering device.
Overview
Radio receivers generally include a tunable band-pass filter with a passband that is wide enough to accommodate the bandwidth of a single station.
4.2The HVD System: Writing Data
A simplified HVD system consists of the following main components:
¢ Blue or green laser (532-nm wavelength in the test system)
¢ Beam splitter/merger
¢ Mirrors
¢ Spatial light modulator (SLM)
¢ CMOS sensor
¢ Photopolymer recording medium
The process of writing information onto an HVD begins with encoding the information into binary data to be stored in the SLM. These data are turned into ones and zeroes represented as opaque or translucent areas on a "page" †this page is the image that the information beam is going to pass through.
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Once the page of data is created, the next step is to fire a laser beam into a beam splitter to produce two identical beams. One of the beams is directed away from the SLM †this beam becomes the reference beam. The other beam is directed toward the SLM and becomes the information beam. When the information beam passes through the SLM, portions of the light are blocked by the opaque areas of the page, and portions pass through the translucent areas. In this way, the information beam carries the image once it passes through the SLM
Page data (left) stored as a hologram (right)
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When the reference beam and the information beam rejoin on the same axis, they create a pattern of light interference †the holography data. This joint beam carries the interference pattern to the photopolymer disc and stores it there as a hologram.
A memory system isn't very useful if you can't access the data you've stored. In the next section, we'll find out how the HVD data-retrieval system works.
4.3The HVD System: Reading Data
To read the data from an HVD, you need to retrieve the light pattern stored in the
hologram.
In the HVD read system, the laser projects a light beam onto the hologram †a light beam that is identical to the reference beam (Read System 1 in the image above). The hologram diffracts this beam according to the specific pattern of light interference it's storing. The resulting light recreates the image of the page data that established the light-interference pattern in the first place. When this beam of light †the reconstruction
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Page data stored in an HVD (left) and recreated by CMOS sensor (right) Now let's take a look at how HVD compares to other next-generation storage media. 5.How HVD Compares
While HVD is attempting to revolutionize data storage, other discs are trying to improve upon current systems. Two such discs are Blu-ray and HD-DVD, deemed the next-generation of digital storage. Both build upon current DVD technology to increase storage capacity. All three of these technologies are aiming for the high-definition video market, where speed and capacity count. So how does HVD stack up
Blu-ray HD-DVD HVD
Initial cost for recordable disc Approx. $18 Approx. $10 Approx. $120
Initial cost for Approx. recorder/player 1 $2,000 Approx.
$2,000 Approx.
$3,000
Initial storage capacity 54 GB 30 GB 300 GB
Read/write speed 36.5 Mbps 36.5 Mbps 1 Gbps
Conclusion
Holographic Versatile Disc (HVD) is an advanced optical disc technology still in the research stage which would greatly increase storage over Blu-ray and HD-DVD optical disc systems. It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed amongst the data. A dichroic mirror layer between the holographic data and the servo data reflects the blue-green laser while letting the red laser pass through. This prevents interference from refraction of the blue-green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology .These disks have the capacity to hold up to 3.9 terabytes (TB) of information, which is approximately eighty times the capacity of Blu-ray Disc. The HVD also has a transfer rate of 1 Gbit/s.
FUTURE SCOPE
Dell monitoring advancements in optical technology and expects the cost and performance of CD-RW drives become more competitive with the magnetic formats. Dell plan to offer CD-RW/DVD ROM Combo Drives when reasonably priced. Reliable devices become available. These devices should eventually replace current CD-RW drive and offer convenience, large storage capacity that are backward compatible with previous CD formats, and DVD ROM readability. Dell expects DVD-RAM systems to be adopted by high end users initially. Rambo systems when available are expected to provide another system in a evolution to a universal RMSD providing a larger capacity drive capable of reading and writing to the most popular CD, DVD format.
HVD is still in the late stages of development, nothing is written in stone; but you've probably noticed that the projected introductory price for an HVD is a bit steep. An initial price of about $120 per disc will probably be a big obstacle to consumers. However, this price might not be so insurmountable to businesses, which are HVD developers' initial target audience. Optware and its competitors will market HVD's storage capacity and transfer speed as ideal for archival applications, with commercial systems available as soon as late 2006. Consumer devices could hit the market around 2010.
8, Bibliography
"Alliance touts holographic disc 'revolution'." The Register.
http://theregister.co.uk/2005/02/07/hvd_alliance founded/
"Holographic Storage Standards Eyed." Video/Imaging DesignLine.
http://videsignlineproducts/60405368
Optware Corporation
http://optware.co.jp/english/
Tom's Hardware Guide: HVD
http://tomshardwarebusiness/20050616/dvd_standards-07.html "What is holographic storage" InPhase Technologies. http://inphase-technologiestechnology/index.html wikipedia.com
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CONTENTS
Page
1. INTRODUCTION 01
2. REMOVABLE MEDIA STORAGE DEVICES 02
2.1 Floppy Disk 02
2.2 Optical Formats 02
2.3 CD-ROM 03
2.4 DVD-ROM 03
2.5 DVD-R 04
2.6 DVD-RAM 05
2.7 DVD-RW 05
2.8 +RW 06
2.9 Magneto-Optical Formats 06
3. HOLOGRAPHIC VERSATILE DISC 07
3.1 How Holographic Disc Works 07
3.2 Basics Of Holographic Memory 08
3.3 Holographic Data Storage Basics 10
3.4 Holographic Versatile Disc 12
4. STATUS OF DEVELOPMENT 14
4.1 Holographic Disc Structure 14
4.2 The HVD System Writing Data 17
4.3 The HVD System Reading Data 20
5. HOW HVD COMPARES 22
6. CONCLUSION 23
7. FUTURE SCOPE 24
8. BIBLIOGRAPHY 25
ABSTRACT
Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which would greatly increase storage over Blue-ray Disc and HP DVD optical disc systems. It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used as the reference beam and to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed amongst the data.
A dichroic mirror layer between the holographic data and the servo data reflects the blue-green laser while letting the red laser pass through. This prevents interference from refraction of the blue-green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology.These discs have the capacity to hold up to 3.9 terabyte(TB) of information, which is approximately 6,000 times the capacity of a CD-ROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray Discs, and about 8 times the capacity of standard computer hard drives as of 2006. The HVD also has a transfer rate of 1 gigabit/s. Optware is expected to release a 200 GB disc in early June 2006, and Maxell in September 2006 with a capacity of 300 GB and transfer rate of 20 MB/s.
1. INTRODUCTION
Requirements for removable media storage devices (RMSDs) used with personal computers have changed significantly since the introduction of the floppy disk in 1971. At one time, desktop computers depended on floppy disks for all of their storage requirements. Even with the advent of multi Gigabyte hard drives and fast Internet connections, floppy disks and other RMSDs are still an integral part of most computer systems, providing:
t* Transport between computers for data files and software
Backup to preserve data from the hard disks.
A way to load the operating system software in the event of a hard-drive failure.
Some RMSD options available today are approaching the performance, capacity, and cost of hard-disk drives. Considerations for selecting an RMSD include capacity, speed, convenience, durability, data availability, and backward compatibility. Technology options used to read and write data include:
Magnetic formats that use magnetic particles and magnetic fields. > Optical formats that use laser light and optical sensors.
Magneto-optical and magneto-optical hybrids that use a combination of magnetic and optical properties to increase storage capacity.
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2. REMOVABLE MEDIA STORAGE DEVICES (RMSDs)
Let us have a glance on the different RMSDs.
2.1 Floppy Disk
Floppy disk drives provide faster data access because they access data randomly. Floppy drives provide an average data access speed of less than 100 milliseconds (ms).
The 1.44-MB, 3.5-inch floppy is useful for storing and backing up small data files, can be used to boot computer systems, and has been the standard for data interchange between PCs. However it provides only a fraction of the storage capacity required for many files and most software programs in use today. Storing data on floppy drives also is slow. Data transfer rates average around 0.06 MB/sec.
2.2 Optical Formats
Optical RMSD formats use a laser light source to read and/or write digital data to disc. CD and DVD are two major optical formats. CDs and DVDs have similar compositions consisting of a label, a protective layer, a reflective layer (aluminum, silver, or gold), a digital-data layer molded in polycarbonate, and a thick polycarbonate bottom layer
Label layer
Reflective layer
Digital-data layer
Bottom Of disc Polycarbonate
layer
Optical Disk Composition
CD formats include:
¦ Compact disc-read only memory (CD-ROM)
¦ Compact disc-recordable (CD-R)
¦ Compact disc-rewritable (CD-RW)
DVD formats include:
¦ Digital versatile disc-read only memory (DVD-ROM)
¦ Digital versatile disc-recordable (DVD-R) DVD-RAM (rewritable)
¦ Digital versatile disc-rewritable (DVD-RW)
¦ +RW (rewritable)
2.3 CD-ROM
CD-ROM Standard was established in 1984.They quickly evolved into a low cost digital storage option because of CD-audio industry
Data bits are permanently stored on a CD as a spiral track of physically molded pits in the surface of a plastic data layer that is coated with reflective aluminum. Smooth areas surrounding pits are called lands. CDs are extremely durable because the optical pickup (laser light source, lenses and optical elements, photoelectric sensors, and amplifiers) never touches the disc. Because data is read through the thick bottom layer, most scratches and dust on the disc surface are out of focus, so they do not interfere with the reading process.
One CD-ROM (650-700 MB) storage capacity can store data from more than 450 floppy disks. Data access rate ranges from 80 to 120 ms. Data transfer rates are approximately 6 MB/sec.
2.4 DVD-ROM
The DVD-ROM standard, introduced in 1995 came over as a result of a DVD consortium. Like CD drives, DVD drives read data through the disc substrate reducing interferences from surface dust and scratches. However DVD-ROM technology provides seven times the storage capacity of CDs and accomplishes most of this increase by advancing the technology used for CD systems. The distance between recording tracks is les than half that is used for CDs. The pit size also is less than half
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that of CDs, which requires a reduced laser wavelength read the smaller sized pits. These features alone give DVD-ROM discs 4.5 times the storage capacity of CDs.
DVD drives can also store on both sides of the disc; manufacturers deliver the two-sided structure by bonding two thinner substrates together, providing the potential to double a DVD's storage capacity. Single sided DVD discs have the two fused substrates, but only one side contains data.
In a DVD, storage of data in the data layers can be:
Single-sided, single layer (4.7 GB)
Double-sided, single layer (9.4 GB)
Single-sided, double layer (8.5 GB)
Double-sided, double layer (17 GB)
Single-sided, single layer (4.7GB) Single-sided, double layer (8.5 GB)
0.6mm
0.6mm
Double-sided. Single layer (9.4 GB)
Double.-sided, double layer (1" GB)
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Figure: DVD Data Storage Versions
2.5 DVD-R
DVD-R drives were introduced in 1997 to provide write-once capability on DVD-R discs used for producing disc masters in software development and for multimedia post-production. This technology sometimes referred to as DVD-R for authoring, is limited to niche applications because drives and media are expensive.
DVD-R discs employ a photosensitive dye technology similar to CD-R media. At 3.95 GB per side, the first DVD-R discs provided a little less storage capacity than DVD-ROM discs. That capacity has now been extended to the 4.7-GB capacity of DVD-ROM discs. The IX DVD-R data transfer rate is 1.3 MB/sec. Most DVD-ROM drives and DVD video players read DVD-R discs. Slightly modified DVD-R drives and discs have recently become available for general use.
2.6 DVD-RAM
DVD-RAM (rewritable) drives were introduced in 1998. DVD-RAM devices use a phase change technology combined with some embossed land/pit features. Employing a format termed "land groove", data is recorded in the grooves formed on the disc and on the land between the grooves. The initial disc capacity was
2.6 GB per side, but a 4.7 GB- per-side version is now available.
The 4.7-GB DVD-RAM discs come in cartridges that protect the medium from handling damage, such as fingerprints and scratches. A single-sided disc is expected to be removable from the cartridge so it can also be played in DVD-ROM drives that support DVD-RAM. The double-sided disc, providing 4.7GB of storage capacity per side, is not removable from the cartridge.
Each DVD-RAM disc is reported to handle more than 100,000 rewrites. DVD-RAM is specifically designed for PC data storage; DVD-RAM discs use a storage structure based in sectors, instead of the spiral groove structure used for CD data storage. This sector storage is similar to the storage structure used by hard drives. Sector storage results in faster random data access speed.
Because of their high cost relative to CD-RW technology, current consumer-oriented DVD-RAM drives and media are not a popular choice for PC applications. Slow adoption of DVD-RAM reading capability in DVD-ROM drives has also limited DVD-RAM market acceptance.
2.7 DVD-RW
The DVD-RW drive format is similar to the DVD-R format, but offers rewritability using a phase-change recording layer that is comparable to the phase-change layer used for CD-RW. DVD-RW is intended for consumer video (non -PC) use, but PC applications are also expected for this technology. The first DVD-RW drives based on this format, which also recorded DVD-R discs, were introduced in early 2001.
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2.8 +RW
Sony and Philips were founding members of the DVD consortium, but broke away to introduce the DVD+RW (now called +RW) phase change, rewritable technology in 1997. Discs can be written approximately 1000 times, which makes them a good option for video recording, but not optimal for data storage. +RW technology's strongest feature is its backward compatibility with DVD-ROM drives and DVD video players.
2.9 Magneto-Optical Formats
Magneto-optical (MO) technology combines he strengths of magnetic and optical technologies by using a laser to read data and the combination of a laser and magnetic field to write data. The top (label side) of the disk is exposed to a magnetic field to write data, and a laser light source targets the data layer through the bottom substrate to read data.
There are 3.5- and 5.5-inch disk formats that contain a magnetic alloy layer. Magnetic particles in the alloy are very stable and resist changing polarity at room temperature. Data bits re recorded on this magnetic layer by heating it with a focused laser beam in the presence of magnetic field. Changes in the magnetic orientation of the data bits along a track represents 0s and 1 s much like on hard disks and other magnetic media. The magnetic layer also changes the rotation or polarization of reflected laser light depending on the 0 or 1 polarity of the magnetic bits. This property called the "Kerr Effect" and is used to read the data. MO systems also increase the data bits vertically rather than horizontally.
The 3.5-inch disks are available in 128-, 230-, and 640-MB storage capacities. The 5.25-inch disks come in 650-MB and 1.3-, 2.6-, and 5.2-GB sizes. A 9.1 -GB size is expected soon. At less than 25ms, data access times faster than the average 100ms of phase change CD and DVD technologies. MO drives are widely used in Japan for general-purpose storage, similar to the way Zip drives are used in the U.S. Outside of Japan; applications for MO drives typically have been in niche markets for Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM), document imaging, and high-capacity archives.
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Holographic Versatile Disc 3. HOLOGRAPHIC VERSATILE DISC
3.1How Holographic Versatile Discs Work
Holographic memory systems have been around for decades. They offer tar more storage capacity than CDs and DVDs †even "next-generation" DVDs like Blu-ray †and their transfer rates leave conventional discs in the dust. So why haven't we all been using holographic memory for years now
There are several hurdles that have been holding Holographic versatile disc holographic storage back from the realm of mass
consumption, including price and complexity. Until now, the systems have required a cost-prohibitive level of precision in manufacturing. But recent changes have made the holographic versatile disc (HVD) developed by Optware a viable option for consumers.
In this article, we'll find out how the HVD works, how it has improved upon previous methods of holographic storage and how it stacks up to Blu-ray and HD-DVD
3.2Basics of Holographic Memory
The first step in understanding holographic memory is to understand what "holographic" means. Holography is a method of recording patterns of light to produce a three-dimensional object. The recorded patterns of light are called a hologram.
The process of creating a hologram begins with a focused beam of light ~ a laser beam. This laser beam is split into two separate beams: a reference beam, which remains unchanged throughout much of the process, and an information beam, which passes 3-D image of the Death Star through an image. When light encounters an image, its created by holography composition changes (see How Light Works to learn
about this process). In a sense, once the information beam encounters an image, it carries that image in its waveforms. When these two beams intersect, it creates a pattern of light interference. If you record this pattern of light interference †for example, in a photosensitive polymer layer of a disc - you are essentially recording the light pattern of the image.
To retrieve the information stored in a hologram, you shine the reference beam directly onto the hologram. When it reflects off the hologram, it holds the light pattern of the image stored there. You then send this reconstruction beam to a CMOS sensor to recreate the original image.
Most of us think of holograms as storing the image of an object, like the Death Star pictured above. The holographic memory systems we're discussing here use holograms to store digital instead of analog information, but it's the same concept. Instead of the information beam encountering a pattern of light that represents the
Death Star, it encounters a pattern of light and dark areas that represent ones and zeroes.
Encoded page data
HVD offers several advantages over traditional storage technology. HVDs can ultimately store more than 1 terabyte (TB) of information †that's 200 times more than a single-sided DVD and 20 times more than a current double-sided Blu-ray. This is partly due to HVDs storing holograms in overlapping patterns, while a DVD basically stores bits of information side-by-side. HVDs also use a thicker recording layer than DVDs †an HVD stores information in almost the entire volume of the disc, instead of just a single, thin layer.
The other major boost over conventional memory systems is HVD's transfer rate of up to 1 gigabyte (GB) per second - that's 40 times faster than DVD. An HVD stores and retrieves an entire page of data, approximately 60,000 bits of information, in one pulse of light, while a DVD stores and retrieves one bit of data in one pulse of light.
Now that we know the premise at work in HVD technology, let's take a look at the structure of the Optware disc.
3.3The Holographic Data storage Basics
Prototypes developed by Lucent and IBM differ slightly, but most holographic data storage systems (HDSS) are based on the same concept. Here are 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
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. Some systems use a photopolymer in place of the 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.
An advantage of a holographic memory system is that an entire page of data can be retrieved quickly and at one time. 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-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.
3.4The Holographic Versatile Disc
Holographic memory has been around for more than 40 years, but several characteristics made it difficult to implement in a consumer market. First off, most of these systems send the reference beam and the information beam into the recording medium on different axes. This requires highly complex optical systems to line them up at the exact point at which they need to intersect. Another drawback has to do with incompatibility with current storage media: Traditionally, holographic storage systems contained no servo data, because the beam carrying it could interfere with the holography process. Also, previous holographic memory discs have been notably thicker than CDs and DVDs.
Optware has implemented some changes in its HVD that could make it a better fit for the consumer market. In the HVD system, the laser beams travel in the same axis and strike the recording medium at the same angle, which Optware calls the collinear method. According to Optware, this method requires a less complex system of optics, enabling a smaller optical pickup that is more suited to consumer use.
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HVD optical pickup
HVD also includes servo data. The servo beam in the HVD system is at a wavelength that does not photosensitize the polymer recording medium. In the HVD test system, the servo data is carried in a red (650-nm wavelength) laser. The size and thickness of an HVD is also compatible with CDs and DVDs.
The structure of the disc places a thick recording layer between two substrates and incorporates a dichroic mirror that reflects the blue-green light carrying the holography data but allows the red light to pass through in order to gather servo information.
4.STATUS OF DEVELOPMENT
4.1 Holographic Versatile Disc structure
Disc Structure
Green or
1. Green writing/reading laser (532nm)
2. Red positioning/addressing laser (650nm)
3. Hologram (data)
4. Polycarbon layer
5. Photopolymeric layer (data-containing layer)
6. Distance layers
7. Dichroic layer (reflecting green light)
8. Aluminium reflective layer (reflecting red light)
9. Transparent base
Diagonistic layer
A dichroic filter is a very-accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, Dichroic mirrors and dichroic reflectors tend to be characterized by the color(s) of light that they reflect rather than the color(s) they pass. (See dichroic for the etymology of the term.)
Used in front of a light source, a dichroic filter produces light that is perceived by humans to be highly saturated (intense) in color. Although costly, such filters are popular in architectural and theatrical applications.
Used behind a light source, dichroic reflectors commonly reflect visible light forward while allowing the invisible infrared light (radiated heat) to pass out of the rear of the fixture, resulting in a beam of light that is "cooler". Modern quartz halogen incandescent light bulbs frequently contain an integrated dichroic reflector (see picture).
A dichroic filter is a very-accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, Dichroic mirrors and dichroic reflectors tend to be characterized by the color(s) of light that they reflect rather than the color(s) they pass. (See dichroic for the etymology of the term.)
Used in front of a light source, a dichroic filter produces light that is perceived by humans to be highly saturated (intense) in color. Although costly, such filters are popular in architectural and theatrical applications.
Dichroic filters operate using the principle of interference. Alternating layers of an optical coating are built up upon a glass substrate, selectively reinforcing certain wavelengths of light and interfering with other wavelengths. The layers are usually deposited using a process carried out in a vacuum. By controlling the thickness and number of the layers, the frequency (wavelength) of the passband of the filter can be tuned and made as wide or narrow as desired. Because unwanted wavelengths are reflected rather than absorbed, dichroic filters don't absorb much energy during operation and so don't become nearly as hot as the equivalent conventional filter (which attempts to absorb all energy except for that in the passband).
Filter
An optical filter is a device which selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light, or polarizations), while blocking the remainder. They are commonly used in photography, in many optical instruments, and to colour stage lighting-Optical coating
An optical coating is a thin layer of material placed on an optical component such as a lens or mirror which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and is commonly used on spectacle and photographic lenses. Another type is the high-reflector coating which can be used to produce mirrors which reflect greater than 99% of the light which falls on them. More complex optical coatings exhibit high-reflection over some range of wavelengths, and anti-reflection over another range, allowing the production of dichroic thin-film optical filters.
Passband
In telecommunications, optics, and acoustics, passband is the portion of spectrum, between limiting frequencies that is transmitted with minimum relative loss or maximum relative gain by a filtering device.
Overview
Radio receivers generally include a tunable band-pass filter with a passband that is wide enough to accommodate the bandwidth of a single station.
4.2The HVD System: Writing Data
A simplified HVD system consists of the following main components:
¢ Blue or green laser (532-nm wavelength in the test system)
¢ Beam splitter/merger
¢ Mirrors
¢ Spatial light modulator (SLM)
¢ CMOS sensor
¢ Photopolymer recording medium
The process of writing information onto an HVD begins with encoding the information into binary data to be stored in the SLM. These data are turned into ones and zeroes represented as opaque or translucent areas on a "page" †this page is the image that the information beam is going to pass through.
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Once the page of data is created, the next step is to fire a laser beam into a beam splitter to produce two identical beams. One of the beams is directed away from the SLM †this beam becomes the reference beam. The other beam is directed toward the SLM and becomes the information beam. When the information beam passes through the SLM, portions of the light are blocked by the opaque areas of the page, and portions pass through the translucent areas. In this way, the information beam carries the image once it passes through the SLM
Page data (left) stored as a hologram (right)
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When the reference beam and the information beam rejoin on the same axis, they create a pattern of light interference †the holography data. This joint beam carries the interference pattern to the photopolymer disc and stores it there as a hologram.
A memory system isn't very useful if you can't access the data you've stored. In the next section, we'll find out how the HVD data-retrieval system works.
4.3The HVD System: Reading Data
To read the data from an HVD, you need to retrieve the light pattern stored in the
hologram.
In the HVD read system, the laser projects a light beam onto the hologram †a light beam that is identical to the reference beam (Read System 1 in the image above). The hologram diffracts this beam according to the specific pattern of light interference it's storing. The resulting light recreates the image of the page data that established the light-interference pattern in the first place. When this beam of light †the reconstruction
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Page data stored in an HVD (left) and recreated by CMOS sensor (right) Now let's take a look at how HVD compares to other next-generation storage media. 5.How HVD Compares
While HVD is attempting to revolutionize data storage, other discs are trying to improve upon current systems. Two such discs are Blu-ray and HD-DVD, deemed the next-generation of digital storage. Both build upon current DVD technology to increase storage capacity. All three of these technologies are aiming for the high-definition video market, where speed and capacity count. So how does HVD stack up
Blu-ray HD-DVD HVD
Initial cost for recordable disc Approx. $18 Approx. $10 Approx. $120
Initial cost for Approx. recorder/player 1 $2,000 Approx.
$2,000 Approx.
$3,000
Initial storage capacity 54 GB 30 GB 300 GB
Read/write speed 36.5 Mbps 36.5 Mbps 1 Gbps
Conclusion
Holographic Versatile Disc (HVD) is an advanced optical disc technology still in the research stage which would greatly increase storage over Blu-ray and HD-DVD optical disc systems. It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed amongst the data. A dichroic mirror layer between the holographic data and the servo data reflects the blue-green laser while letting the red laser pass through. This prevents interference from refraction of the blue-green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology .These disks have the capacity to hold up to 3.9 terabytes (TB) of information, which is approximately eighty times the capacity of Blu-ray Disc. The HVD also has a transfer rate of 1 Gbit/s.
FUTURE SCOPE
Dell monitoring advancements in optical technology and expects the cost and performance of CD-RW drives become more competitive with the magnetic formats. Dell plan to offer CD-RW/DVD ROM Combo Drives when reasonably priced. Reliable devices become available. These devices should eventually replace current CD-RW drive and offer convenience, large storage capacity that are backward compatible with previous CD formats, and DVD ROM readability. Dell expects DVD-RAM systems to be adopted by high end users initially. Rambo systems when available are expected to provide another system in a evolution to a universal RMSD providing a larger capacity drive capable of reading and writing to the most popular CD, DVD format.
HVD is still in the late stages of development, nothing is written in stone; but you've probably noticed that the projected introductory price for an HVD is a bit steep. An initial price of about $120 per disc will probably be a big obstacle to consumers. However, this price might not be so insurmountable to businesses, which are HVD developers' initial target audience. Optware and its competitors will market HVD's storage capacity and transfer speed as ideal for archival applications, with commercial systems available as soon as late 2006. Consumer devices could hit the market around 2010.
8, Bibliography
"Alliance touts holographic disc 'revolution'." The Register.
http://theregister.co.uk/2005/02/07/hvd_alliance founded/
"Holographic Storage Standards Eyed." Video/Imaging DesignLine.
http://videsignlineproducts/60405368
Optware Corporation
http://optware.co.jp/english/
Tom's Hardware Guide: HVD
http://tomshardwarebusiness/20050616/dvd_standards-07.html "What is holographic storage" InPhase Technologies. http://inphase-technologiestechnology/index.html wikipedia.com
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CONTENTS
Page
1. INTRODUCTION 01
2. REMOVABLE MEDIA STORAGE DEVICES 02
2.1 Floppy Disk 02
2.2 Optical Formats 02
2.3 CD-ROM 03
2.4 DVD-ROM 03
2.5 DVD-R 04
2.6 DVD-RAM 05
2.7 DVD-RW 05
2.8 +RW 06
2.9 Magneto-Optical Formats 06
3. HOLOGRAPHIC VERSATILE DISC 07
3.1 How Holographic Disc Works 07
3.2 Basics Of Holographic Memory 08
3.3 Holographic Data Storage Basics 10
3.4 Holographic Versatile Disc 12
4. STATUS OF DEVELOPMENT 14
4.1 Holographic Disc Structure 14
4.2 The HVD System Writing Data 17
4.3 The HVD System Reading Data 20
5. HOW HVD COMPARES 22
6. CONCLUSION 23
7. FUTURE SCOPE 24
8. BIBLIOGRAPHY 25
