CD & DVD
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CD & DVD!
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CD-COMPACT DISK
About
A compact disc [sometimes spelled disk] (CD) is a small, portable, round medium made of molded polymer (close in size to the floppy disk) for electronically recording, storing, and playing back audio, video, text, and other information in digital form. Tape cartridges and CDs generally replaced the phonograph record for playing back music. At home, CDs have tended to replace the tape cartridge although the latter is still widely used in cars and portable playback devices.
Initially, CDs were read-only, but newer technology allows users to record as well. CDs will probably continue to be popular for music recording and playback. A newer technology, the digital versatile disc (DVD), stores much more in the same space and is used for playing back movies.
Some variations of the CD include:
* CD-ROM * CD-i * CD-RW * CD-ROM XA * CD-W * Photo CD * Video CD
History
The history of the compact disk (CD) started with the videodisk in the form of Video Long Play (VLP) read-only systems. The videodisk did not become a commercial success, even once a few write-once optical disks of different formats and sizes were introduced. These were analog systems.
In about 1982, the CD-DA (compact disk-digital audio) was introduced to the market jointly by Phillips and Sony. It stored a high-quality stereo audio signal in a digital form. These systems became a huge success.
In 1985, the compact disk-digital audio technology was extended for computer storage, thanks again to cooperation between Phillips and Sony. This was called a CD-ROM (compact disk-read only memory) and later became a standard ECMA-119, which specifies the CD-ROM physical format. The logical format of the CD-ROM is specified in the ISO standard 9660 and allows data access through file name and directories.
The next step, CD-I (compact disk-interactive) was again created by Philips and Sony and announced in 1986. The CD-ROM/XA (/extended architecture) was introduced in 1988. Philips, Sony, and Microsoft specified digital optical formats for several media and published the specifications.
CD-WORM (write once read many times) technology was initiated in 1990, as well as CD-MO (magneto-optical). The main reason for the great success of CD-DA and CD-ROM technology is a set of standards jointly developed by Sony and Phillips which, essentially specify the following:
* Macroscopic and microscopic physical structure and design of the compact disk. * Compact disk data format that specifies space for data, address information, and error correction codes. * Error correction code (ECC) scheme, with room for additional data and ECC.
The CD-ROM standards, also created by Sony and Phillips, use the same disk and scanning technology, and the same mastering and replication technique as used for CD-DA. The only difference between CD-DA and CD-ROM is in the data format, more powerful ECC, and more precise data addressing for CD-ROM. Most of the following explanation applies equally applied to CD-DA and CD-ROM.
Basic Design
The figures below illustrate the structure and operating principles of the compact disk. The CD is 12 cm in diameter, 1.2 mm thick, has a center hole 15 mm in diameter, and spins at a constant linear velocity (CLV) or constant angular velocity (CAV). Unlike the hard disk or floppy disk, there is only one track on the optical disk and all data are stored in a spiral of about 2 billion small shallow pits on the surface. There are about 20,000 windings on a CD - all part of the same track. This translates into about 16,000 tracks per inch (TPI) of track density and an areal density of 1 Mb/mm2. The total length of the track on a CD is almost 3 miles (~4.5 km).
A transparent polycarbonate (PC) polymeric substrate (layer) has the pits molded onto its surface. These pits are the coded data and carry the information. The areas in between the pits, which are 0.9 mm (microns) to 3.3 mm long, are called "lands". The substrate layer is covered with a thin reflective layer of metal (aluminum) and with a protective layer of lacquer. On top of the CD sits the label layer.
Summarizing, the compact disk consists of:
* The label * The protective layer * The reflective layer * The substrate layer.
A laser beam of approximately 780 nm wave length is focused on the data side of the disk into a spot of about 1 micron in diameter. The laser moves in the radial direction over the fast spinning disk and scans the data track for the intensity of the reflected light.
The data pits are about 0.12 microns (120 nanometers) deep and about 0.6 microns wide. The distance between the neighboring windings of the track is about 1.6 microns. The laser beam scattering occurs when it scans the pits, which translates into a slight drop in intensity of the reflected beam.
The change in reflected light intensity occurs every time the laser spot moves from the pit onto the land and vice versa. The high-frequency modulated signal produced by these changes in light intensity represents the data stored on the CD.
The reason for the high reliability of the CD is good protection of the data from damage both inside and outside CD drive. Outside, the data layer is protected by tough 1.2 mm thick layer of polycarbonate on one side and 10-20 microns of a protective lacquer layer on the other side. Small scratches on the surface of CD do not directly erase the data, but just create additional areas of light scattering. This can confuse the drive's electronic, which is also much less sensitive to radial scratches than to the circumferential ones. Gentle polishing of the scratch can (in many cases) make the CD readable again. But, this is rarely necessary thanks to the large size of the laser spot on the surface of the PC layer - about 1 mm. This large spot diameter "integrates" the signal over the large area making the system much less sensitive to dirt and scratches on the disk surface.
Inside the drive, the disk and the drive's optics are separated by a distance of about 1 mm, making mechanical interaction and "crashes", even with wavy disks and imperfect clamping almost impossible.
Understanding the CD
As discussed in How Analog and Digital Recording Works, a CD can store up to 74 minutes of music, so the total amount of digital data that must be stored on a CD is:
44,100 samples/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute = 783,216,000 bytes
To fit more than 783 megabytes (MB) onto a disc only 4.8 inches (12 cm) in diameter requires that the individual bytes be very small. By examining the physical construction of a CD, you can begin to understand just how small these bytes are.
A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. We'll return to the bumps in a moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic. A cross section of a complete CD (not to scale) looks like this: en printed onto the acrylic. A cross section of a complete CD (not to scale) looks like this:
Understanding the CD: The Spiral
A CD has a single spiral track of data, circling from the inside of the disc to the outside. The fact that the spiral track starts at the center means that the CD can be smaller than 4.8 inches (12 cm) if desired, and in fact there are now plastic baseball cards and business cards that you can put in a CD player. CD business cards hold about 2 MB of data before the size and shape of the card cuts off the spiral.
What the picture on the right does not even begin to impress upon you is how incredibly small the data track is -- it is approximately 0.5 microns wide, with 1.6 microns separating one track from the next. (A micron is a millionth of a meter.) And the bumps are even more miniscule...
Multi-Beam technology
Traditional CD and DVD drives employ a single laser beam directed at one track which forms a continuous spiral on the disc.
Instead of illuminating a single track on the surface of a CD-ROM or DVD-ROM disks, the technology, proposed by Zen Research illuminates multiple tracks, detects bits simultaneously, and reads them in parallel. This technology can be used without changes to the CD or DVD disk standards or basic drive design, and works with both CAV (Constant Angular Velocity) and CLV (Constant Linear Velocity, preferred by Zen to deliver constant data transfer rates across the disk). Multibeam technology at CLV enables optical drives to read and transfer data from the disc at a constant speed, which corresponds to the drive's true spin X-rating.
Increase in the data rates due to the multi-beam approach allows to reduce disk spin rates, and decrease associated with high speed vibration and noise.
The TrueX Multibeam method uses a conventional laser beam sent trough a diffraction grating which splits the beam into seven evenly spaced beams. These beams illuminate seven different tracks simultaneously. On their way to the disk surface, beams pass through a beam splitting mirror to the objective lens and towards the disk surface. Focus and tracking are performed using the central beam. Three beams on each side of the central beam are readable by a detector array if the center beam is in focus and on the track. On the way back, the reflected beams reach the multiple beam detector array, which consists of seven discrete detectors - one for each beam.
By reading seven tracks at once, the TrueX Multibeam drive achieves much higher data transfer rates than a conventional drive spinning at the same rate. Similarly, the TrueX Multibeam drive, operating at lower speed, can achieve the same data rate as a conventional drive and keep vibration and noise at much lower level.
Currently, Kenwood Technologies Inc., a subsidiary of Kenwood Corporation, offers a Zen-enabled TrueX Multibeam CD-ROM drives.
Making CDs
One reason for the success of the optical disk technology is the ease and cheapness of replicating them in large quantities. The making of a CD includes 2 main steps: Pre-mastering and Mastering.
First, a layer of light-sensitive photoresist is spin-coated onto the clean glass master-disk from a solvent solution.
Then, the photoresist is exposed to a modulated beam of a short-wavelength light, which carries the encoded data. Next, the master is developed in a wet process by exposing it to the developer, which etches away exposed areas thus leaving the same pattern we will find later on the CD. Next, the master is coated (using electroplating technique) with a thick (about 300 um) metal layer to form a stamper - a negative replica of the disk. The photoresist layer is destroyed during this process, but the much more durable stamper is formed and can be used for CD replication. Usually, a stamper can be used to produce a few tens of thousands CDs before it wears out.
Finally, the process of injection molding is used to produce a surface of the compact disk. Hot plastic (PC) is injected into a mold, and then is pressed against the stamper and cooled, resulting in the CD. Other processes than injection molding could be used, but they all involve pressing the hot plastic against the stamper.
At the very end, the pits and lands on the surface of a CD are coated with a thin reflective metal layer (aluminum), then coated with lacquer and supplied with the label. Packaging usually finishes the process of making a CD.
DVD-Digital Versatile Disc
About
DVD, also known as Digital Versatile Disc or Digital Video Disc, is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage. DVDs are of the same dimensions as compact discs (CDs), but store more than six times as much data. After a lifespan of ten years, during which time the capacity of hard disks increased a hundred-fold, the CD-ROM finally got the facelift it required to take it into the next century when a standard for DVD (initially called digital video disc but eventually known as digital versatile disc) was finally agreed during 1996. For computer users DVD means more than just movies, and whilst DVD-Video grabbed most of the early headlines it was through the sale of DVD-ROM drives that the format made a bigger immediate impact in the marketplace. In the late-1990s computer-based DVD drives outsold home DVD-Video machines by a ratio of at least 5:1 and, thanks to the enthusiastic backing of the computer industry in general and the CD-ROM drive manufacturers in particular, by early in the new millennium there were more DVD-ROM drives in use than CD-ROM drives. DVD formats include DVD-Video (often simply called DVD), DVD-ROM, and DVD-Audio. DVD-Video discs hold digitized movies or video programs and are played using a DVD player hooked up to a standard television receiver. In a sense, DVD-Video players are the successors to the videocasette recorders (VCRs) that play VHS tapes. DVD-ROM [Read Only Memory] discs hold computer data and are read by a DVD-ROM drive hooked up to a computer. These disks can only be read—the disks are impressed with data at the factory but once written cannot be erased and rewritten with new data. DVD-ROM also includes recordable variations. DVD-R [Recordable] discs can be written to sequentially but only once. DVD-RAM [Random Access Memory], DVD-RW, and DVD+RW [ReWritable] discs can be written to thousands of times; they differ in their technical standards and, as a result, in the amount of information they can hold. Many DVD recorders can record in several different recordable DVD formats. Some recorders include computer hard drives that allow the user to record tens to hundreds of hours of material temporarily; the user can then select the material that will be transferred to a DVD
History
When Philips and Sony got together to develop CD, there were just the two companies talking primarily about a replacement for the LP. Decisions about how the system would work were carried out largely by engineers and all went very smoothly. The specification for the CD's successor went entirely the other way, with arguments, confusions, half-truths and Machiavellian intrigue behind the scenes.
It all started badly with Matsushita Electric, Toshiba and the movie-makers Time/Warner in one corner, with their Super Density Disc (SD) technology, and Sony and Philips in the other, pushing their Multimedia CD (MMCD) technology. The two disc formats were totally incompatible, creating the possibility of a VHS/Betamax-type battle.
Under pressure from the computer industry, the major manufacturers formed a DVD Consortium to develop a single standard. The DVD-ROM standard that resulted at the end of 1995 was a compromise between the two technologies but relied heavily on SD. The likes of Microsoft, Intel, Apple and IBM gave both sides a simple ultimatum: produce a single standard, quickly, or don't expect any support from the computer world. The major developers, eleven in all, created an uneasy alliance under what later became known as the DVD Forum, continuing to bicker over each element of technology being incorporated in the final specification.
The reasons for the continued rearguard actions was simple. For every item of original technology put into DVD, a license fee has to be paid to the owners of the technology. These license fees may only be a few cents per drive but when the market amounts to millions of drives a year, it is well worth arguing over. If this didn't make matters bad enough, in waded the movie industry.
Paranoid about losing all its DVD-Video material to universal pirating, Hollywood first decided it wanted an anti-copying system along the same lines as the SCMS system introduced for DAT tapes. Just as that was being sorted out, Hollywood became aware of the possibility of a computer being used for bit-for-bit file copying from a DVD disc to some other medium. The consequence was an attempt to have the U.S. Congress pass legislation similar to the Audio Home Recording Act (the draft was called "Digital Video Recording Act") and to insist that the computer industry be covered by the proposed new law.
Whilst their efforts to force legislation failed, the movie studios did succeed in forcing a deeper copy protection requirement into the DVD-Video standard, and the resultant Content Scrambling System (CSS) was finalised toward the end of 1996. Subsequent to this, many other content protection systems have been developed.
Technology
DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing for a DVD's increased storage capacity.
In comparison, Blu-ray, the successor to the DVD format, uses a wavelength of 405 nm, and one dual-layer disc has a 50 GB storage capacity.
Writing speeds for DVD were 1×, that is, 1350 kB/s (1,318 KiB/s), in the first drives and media models. More recent models, at 18× or 20×, have 18 or 20 times that speed. Note that for CD drives, 1× means 150 KiB/s (153.6 kB/s), approximately 9 times slower.
Multi-Beam technology
Traditional CD and DVD drives employ a single laser beam directed at one track which forms a continuous spiral on the disc.
Instead of illuminating a single track on the surface of a CD-ROM or DVD-ROM disks, the technology, proposed by Zen Research illuminates multiple tracks, detects bits simultaneously, and reads them in parallel. This technology can be used without changes to the CD or DVD disk standards or basic drive design, and works with both CAV (Constant Angular Velocity) and CLV (Constant Linear Velocity, preferred by Zen to deliver constant data transfer rates across the disk). Multibeam technology at CLV enables optical drives to read and transfer data from the disc at a constant speed, which corresponds to the drive's true spin X-rating.
Increase in the data rates due to the multi-beam approach allows to reduce disk spin rates, and decrease associated with high speed vibration and noise.
The TrueX Multibeam method uses a conventional laser beam sent trough a diffraction grating which splits the beam into seven evenly spaced beams. These beams illuminate seven different tracks simultaneously. On their way to the disk surface, beams pass through a beam splitting mirror to the objective lens and towards the disk surface. Focus and tracking are performed using the central beam. Three beams on each side of the central beam are readable by a detector array if the center beam is in focus and on the track. On the way back, the reflected beams reach the multiple beam detector array, which consists of seven discrete detectors - one for each beam.
By reading seven tracks at once, the TrueX Multibeam drive achieves much higher data transfer rates than a conventional drive spinning at the same rate. Similarly, the TrueX Multibeam drive, operating at lower speed, can achieve the same data rate as a conventional drive and keep vibration and noise at much lower level.
Currently, Kenwood Technologies Inc., a subsidiary of Kenwood Corporation, offers a Zen-enabled TrueX Multibeam CD-ROM drives.
DVD authoring
DVD authoring is the process of creating a DVD video capable of playing on a DVD player. DVD authoring software must conform to the specifications set by the DVD Forum group in 1995. The complexity of these specifications results from the number of companies that were involved in creating them.
Strictly speaking, DVD authoring differs from the process of MPEG encoding, but as of 2009[update] most DVD authoring software has a built-in encoder (though separate encoders are still used when better quality or finer control over compression settings is required).
Most DVD-authoring applications focus exclusively on video DVDs and do not support the authoring of DVD-Audio discs.
Stand-alone DVD recorder units generally have basic authoring functions, though the creator of the DVD has little or no control over the layout of the DVD menus, which generally differ between models and brands.
The DVD specification
To develop a DVD application (software or hardware), one must first licence the particular book of DVD specifications from DVD Format/Logo Licensing Corporation, a Japanese corporation. The different DVD formats have different books; each book contains hundreds of pages and costs approximately $5000. After obtaining this licence, the developer must become a licensee — which requires an additional fee. Without becoming a licensee, the book can be used only for reference, not for actual creation of DVD applications.
The DVD specifications were written in Japanese and then translated to English for use in America. This process has resulted in text that can be difficult to interpret, and to this day, many companies interpret various parts of the specifications in different ways. This is the reason DVD players from different manufacturers do not always conform to the same rules – each developer understands the specifications in a slightly different way.
External Links:
SDB:Burning DVDs with SuSE Linux
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