diff between cd and dvd with details on each of them

Discussion in 'Electronics Forum' started by Guest, Jul 27, 2006.

  1. Guest

    Guest Guest

    Although both CD and DVD have the same media size and shape, the similarity ends there. There are numerous points of difference between the two, as listed below:
    Data pits and lasers
    A disc has microscopic grooves that move along in a spiral around the disc. Both CDs and DVDs have these grooves. Laser beams are applied to scan these grooves. As you may be aware, digital information is represented in ones and zeroes. In these discs, very tiny reflective bumps (called ‘lands’) and non-reflective holes (called ‘pits’), which are found alongside the grooves, reflect the ones and zeros of digital information.
    Here lies the difference – by reducing the wavelength of the laser (from the 780mm infrared light used in the CD) to 625mm or more infrared light, DVD technology has managed to write in smaller ‘pits’ as compared to the standard CD. This allows for a greater amount of data per track. The minimum length of a pit in a single layer DVD-RAM is 0.4 micron, as compared to 0.834 micron for a CD.
    Also, the tracks of DVDs are narrower, allowing for more tracks per disc, which again translates into more capacity than a CD.
    Layers
    As explained above, DVDs have smaller ‘pits’ and the lasers have to focus on them. This is done by using a thinner plastic substrate than in a CD, which means that the laser has to pass through a thinner layer, with less depth to reach the pits. It was this reduction in thickness which was responsible for discs that were only 0.6mm thick – half that of a CD.
    Data access speeds
    DVDs access data at a much faster rate that do CDs. Here is a comparison – a 32X CD-ROM drive reads data at 4M bytes per second while a 1X DVD drive reads at 1.38M bytes per second. That’s even faster than an 8x CD drive!
    UDF (Universal Data Format)
    Recording formats of CDs and DVDs are quite different. DVDs use UDF (Universal Data Format). This allows data, video, audio or a combination of all three, to be stored in a single file structure. The advantage of this is that any file can be accessed by any drive, computer or consumer video. CDs, however, are not compatible with this format.
    BASIC DEFINITIONS
    What does DVD mean?
    The keyword is "versatile." Digital Versatile discs provide superb video, audio and data storage and access -- all on one disc.
    What's the basic difference between DVD and CD?
    DVD is a high capacity multimedia data storage medium. It can accommodate a complete movie on a single disc, content rich multimedia or very high quality multi-channel audio.
    Can I play CDs on my DVD player?
    Most DVD hardware will play audio CDs and CD-ROMs. The physical dimensions are identical to compact discs. But you should check with your DVD brand's dealer to confirm compatibility with CDs.

    MARKET OUTLOOK
    What's the market outlook for DVD?
    The market for DVD has grown faster than CD or VHS did in their first two years in the USA, Europe and Asia.
    A recent market research study predicts that DVD will become the standard home video format, replacing video cassettes within the next five years.
    Sales of DVD hardware will reach 46 million units in 2000, including 21 million in the United States and 17 million in Europe, according to the report. (The different formats included in this forecast.)
    The research also predicts that worldwide shipments of set top DVD players will increase by 300 per cent in 2000 and retail revenues across the United States, Europe and Japan will rise by 220 percent to $7 billion.

    TECHNICAL DEFINITIONS
    How does DVD technology differ from CD?
    Like CDs, DVDs store data in microscopic grooves running in a spiral around the disc. All DVD drive types use laser beams to scan these grooves: Minuscule reflective bumps (called lands) and nonreflective holes (called pits) aligned along the grooves represent the zeros and ones of digital information.
    But that's where the similarities end. DVDs use smaller tracks (0.74 microns wide, compared to 1.6 microns on CDs) as well as new modulation and error correction methods. These technologies allow them to store data seven times as large as that of a CD. The narrow tracks require special lasers--which can't read CD-ROMs, CD-Rs, CD-RWs, or audio CDs. DVD drive makers managed to solve the problem.

    DVD FORMATS
    How do the various DVD formats differ?
    DVD Video
    For viewing movies and other visual entertainment. The total capacity is 17 Gbytes if two layers on both sides of the disk are utilized.
    DVD-ROM
    Its basic technology is the same as DVD Video, but it also includes computer-friendly file formats. It is used to store data. This product should supplant conventional CD-ROMs in the near future.
    DVD-R
    Its capacity is 4.7 Gbytes. Originally designed for professional authoring, a version for general consumer use is now under development. As with CD-R, users can write only once to this disk.
    DVD-RAM
    This makes DVD a virtual hard disk, with a random read-write access. Originally a 2.6-Gbyte drive, its capacity has increased to 4.7-Gbyte-per-side. It can be re-written more than 100,000 times.
    DVD-RW
    Similar to DVD-RAM except that its technology features a sequential read-write access more like a phonograph than a hard disk. Its read-write capacity is 4.7 Gbytes per side. It can be re-written up to about 1,000 times.
    DVD Audio
    The latest audio format more than doubles the fidelity of a standard CD. It is expected to become the most popular audio disk.

    DVD MULTI
    Is DVD Multi a new format?
    DVD Multi is not a new format, but a set of specifications that will define which drives will read and write which disks for the various DVD consumer and computer applications.
    DVD Multi is targeted at providing broader compatibility across DVD disks, and will embrace all existing format versions.

    DVD PERFORMANCE
    What's the storage capacity of DVD?
    A DVD can store over two hours of video on one layer of the disc.
    A CD can store just 74 minutes of data -- just enough to hold Beethoven's Ninth Symphony.
    Why is DVD video superior to that of standard videotape?
    DVD video storage provides resolution which is far greater than that offered by laser disc media and almost twice the resolution of standard VHS videotape.
    This resolution is dependent on the capabilities of the television monitor used, but you need not have a new monitor to enjoy the benefits of DVD. DVD video also provides low noise.
    One more advantage is that a DVD disc is not physically touched while it spins in the player, so there is no wear and tear or loss of fidelity over time. In contrast, videotapes do touch a playback mechanism and eventually break down, degrading the quality of picture.

    DVD'S IMPORTANCE TO VARIOUS INDUSTRIES
    How is DVD meeting the needs of various industries?
    Movies -- The movie industry needs a disc capable of holding a full length movie of execellent quality video with surround sound audio. DVD Video meets this need.
    Computers -- The computer industry needs higher capacity for the increasingly complex multimedia applications which are now being developed. DVD-ROM meets this need. The computer industry also needs new recordable and re-writable versions of DVD for data storage and archival. DVD-RAM and DVD-R meet this need.
    Entertainment -- The entertainment industry needs DVD for new video games with better and more realistic video content. DVD-ROM meets this need. The music industry wants a higher quality format than CD, as well as increased BASIC DEFINITIONS
    Why DVD is better than VHS:
    it looks better
    it has random access
    it can run on a computer
    cheaper for volume copies and shipping
    almost indestructable
    High Resolution Digital Quality
    8 languages/ 32 subtitles
    security/copyright protected

    Why DVD is better than VHS and CD:
    can hold many times the material
    can play on a DVD player
    full motion/full screen video
    5.1 channel surround sound
    runs on any operating system with no software to download
    standards have been set
    can store any application files (Powerpoint, PDFs, etc.)
    DVD
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    DVD (also known as "Digital Versatile Disc" or "Digital Video Disc") is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. DVDs resemble compact discs as their physical dimensions are the same (120 mm (4.72 inches) or occasionally 80 mm (3.15 inches) in diameter) but they are encoded in a different format and at a much higher density. The official DVD specification is maintained by the DVD Forum.
    [edit]
    History
    Contents
    [hide]
    • 1 History
    • 2 DVD recordable and rewriteable
    • 3 Dual layer recording
    • 4 DVD-Video
    o 4.1 Restrictions
     4.1.1 Content-scrambling system
     4.1.2 Disabled user operations
    • 5 Region codes
    • 6 DVD-Audio
    o 6.1 Security
    • 7 Players and recorders
    • 8 Competitors and successors
    • 9 Direct-to-DVD
    • 10 See also
    • 11 References
    • 12 External links
    o 12.1 Official
    o 12.2 Technology
    o 12.3 Other


    In the early 1990s two high density optical storage standards were being developed: one was the MultiMedia Compact Disc (MMCD), backed by Philips and Sony, and the other was the Super Density disc (SD), supported by Toshiba, Time-Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC. IBM's president, Lou Gerstner, acting as a matchmaker, led an effort to unite the two camps behind a single standard, anticipating a repeat of the costly format war between VHS and Betamax in the 1980s.
    Philips and Sony abandoned their MMCD format and agreed upon Toshiba's SD format (not to be confused with secure digital cards) with two modifications that are both related to the servo tracking technology. The first one was the adoption of a pit geometry that allows "push-pull" tracking, a proprietary Philips/Sony technology. The second modification was the adoption of Philips' EFMPlus. EFMPlus, created by Kees Immink, who also designed EFM, is 6% less efficient than Toshiba's SD code, which resulted in a capacity of 4.7 GB as opposed to SD's original 5 GB. The great advantage of EFMPlus is its great resilience against disc damage such as scratches and fingerprints. The result was the DVD specification Version 1.5, announced in 1995 and finalized in September 1996. In May 1997, the DVD Consortium was replaced by the DVD Forum , which is open to all companies.
    "DVD" was originally an initialism for "Digital Video Disc." Some members of the DVD Forum believe that it should stand for "Digital Versatile Disc" to reflect its widespread use for non-video applications. Toshiba, which maintains the official DVD Forum site [1], adheres to the latter interpretation, and indeed this appeared within the copyright warnings on some of the earliest examples. However, the DVD Forum never reached a consensus on the matter, and so today the official name of the format is simply "DVD"; the letters do not officially stand for anything.[2]
    The first DVD players and discs were available in November 1996 in Japan, March 1997 in the United States, 1998 in Europe and in 1999 in Australia. The first pressed DVD release was the film Twister in 1996. The film had the first test for 2.1 surround sound. The first titles released in the U.S., on March 19, 1997, by Lumivision, authored by AIX Entertainment, were IMAX adaptations: Africa: The Serengeti, Antarctica: An Adventure of a Different Nature, Tropical Rainforest, and Animation Greats.
    By the spring of 1999 the price of a DVD player had dropped below $300 US. At that point Wal-Mart began to offer DVD players for sale, but DVDs represented only a small part of their video inventory; VHS tapes of films made up the remainder. Wal-Mart's competitors followed suit, and DVDs began to increase in popularity with American consumers.
    DVD rentals first topped those of VHS during the week of June 15, 2003 (27.7 M rentals DVD vs. 27.3 M rentals VHS). Major U.S. retailers Circuit City and Best Buy stopped selling VHS tapes in 2002 and 2003, respectively. In June 2005, Wal-Mart and several other retailers announced plans to phase out the VHS format entirely, in favor of the more popular DVD format. However, blank VHS tapes are still widely available since DVD video recorders are significantly less common than DVD players. Many films released to theaters from 2004 onwards are released solely to DVD format and not to VHS format. Consumers have predicted that 2006 would be the final year for new releases on VHS.
    According to the Digital Entertainment Group (DEG), all DVD sales and rentals (films, television series, special interests, etc) totaled $21.2 billion in 2004. The sales portion of that was $15.5 billion. In comparison, the total 2004 US box office for theatrical rentals was $9.53 billion (per the National Association of Theater Owners or NATO). While the growth of theatrical films on DVD has cooled recently, that of television programs and music video has increased dramatically.
    As of 2006, some retailers, such as Circuit City, no longer offer titles on VHS media, instead concentrating solely on DVDs. The price of a DVD player has dropped to below the level of a typical VCR (although DVD recorders are still usually more expensive than VCRs); a low-end player with reasonable quality can be purchased for under $35 US in many retail stores and many modern computers are sold with DVD-ROM drives. Also popular are units that have integrated a DVD and VHS VCR into a single device; these can be purchased for under $100 US. Most, but not all, movie "sets" or series have been released in boxed sets, as have some entire seasons or selected episode volumes of older and newer television programs.
    [edit]
    DVD recordable and rewriteable


    DVD-R read/write side
    Main article: DVD recordable
    Initially developed for the need of data storage for back-up and transport, DVD recordables are now also used for consumer audio and video recording. Three formats were developed: -R/RW (dash), +R/RW (plus), -RAM (random access memory).
    [edit]
    Dual layer recording
    This section does not cite its references or sources.
    You can help Wikipedia by introducing appropriate citations.
    Dual Layer recording allows DVD-R and DVD+R discs to store significantly more data, up to 8.5 Gigabytes per disc, compared with 4.7 Gigabytes for single-layer discs. DVD-R DL (dual layer — see figure) was developed for the DVD Forum by Pioneer Corporation, DVD+R DL (double layer — see figure) was developed for the DVD+RW Alliance by Sony.
    DVD recordable discs supporting this technology are backward compatible with some existing DVD players and DVD-ROM drives. Many current DVD recorders support dual-layer technology, and the price point is comparable to that of single-layer drives, though the blank media remains significantly more expensive. Currently the technology has severe problems with compatibility in hardware DVD players.[citation needed]
    The layer change mechanism in some DVD players can show a noticeable pause, as long as two seconds by some accounts. More than a few viewers have worried that their dual layer discs were damaged or defective. An oft-cited example can be found in the film Black Hawk Down, during the scene when a soldier's arm is severed and another soldier picks it up.
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    DVD-Video


    Example of how producer could show the consumer full compatibility with DVD-Video specification.


    The way Windows shows the contents of a video DVD.
    DVD-Video discs require a DVD-drive and an MPEG-2 decoder (e.g. a DVD-player, or a DVD computer drive with a software DVD player). Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and audio of varying formats (often multi-channel formats as described below). Typical data rates for DVD movies range from 3–10 Mbit/s, and the bit rate is usually adaptive. The typical video resolution for an NTSC disc is 720 × 480, while a PAL disc is 720 × 576. The specifications for video files on a DVD can be any of the following:
    • Up to 9.8 Mbit/s (9800 kbit/s) MPEG-2 video
    • Up to 1.856 Mbit/s (1856 kbit/s) MPEG-1 video
    • PAL:
    720 × 576 pixels MPEG-2 (Called full D1)
    704 × 576 pixels MPEG-2
    352 × 576 pixels MPEG-2 (Called Half-D1, same as the China Video Disc standard)
    352 × 288 pixels MPEG-2
    352 × 288 pixels MPEG-1 (Same as the VCD Standard)
    • NTSC:
    720 × 480 pixels MPEG-2 (Called full D1)
    704 × 480 pixels MPEG-2
    352 × 480 pixels MPEG-2 (Called Half-D1, same as the China Video Disc standard)
    352 × 240 pixels MPEG-2
    352 × 240 pixels MPEG-1 (Same as the VCD Standard)
    All MPEG video must be 25 frames per second on PAL DVDs. On NTSC DVDs MPEG-2 video can be either 29.97 frames per second or 23.976 frames per second, (with the player repeating frames via 3:2 pulldown to achieve NTSC's standard 29.97 frames per second) while MPEG-1 video can only be 29.97 frames per second. Interlacing is only supported for MPEG-2 video on both PAL and NTSC DVDs. 16:9 anamorphic video is only supported at 720x576/480. Note that some DVD-hardware or software players may play discs whose MPEG files do not conform to the above standards- however these discs are non-compliant with the specification for DVD-video. Some hardware players will now play DVD-ROMs or CD-ROMs containing MPEG video files - these are 'unauthored' and lack the file structure that defines a DVD-video. (These files contain extra information, such as the number of video tracks, chapters and links to extra features, which DVD players use to navigate a DVD-video).
    A high number of audio tracks or a large amount of extra material on the disc will often result in a lower bit rate (and image quality) for the main feature. The total bitrate including video, audio and subtitles can be a maximum of 10.08 Mbit/s (10080 kbit/s).
    The audio data on a DVD movie can be PCM, DTS, MPEG-1 Audio Layer II (MP2), or Dolby Digital (AC-3) format. In countries using the PAL system standard DVD-Video releases must contain at least one audio track using the PCM, MP2, or AC-3 format, and all standard PAL players must support all three of these formats. A similar standard exists in countries using the NTSC system, though with no requirement mandating the use or support for the MP2 format. The vast majority of commercial DVD-Video releases today employ AC-3 audio. The official allowed formats for the audio tracks on a DVD Video are:
    • PCM: 48 kHz or 96 kHz sampling rate, 16 bit or 24 bit L-PCM, 2 to 6 channels, up to 6144 kbit/s
    • AC-3: 48 kHz sampling rate, 1 to 5.1 (6) channels, up to 448 kbit/s
    • DTS: 48 kHz sampling rate, 2 to 6 channels, Half Rate (768 kbit/s) or Full Rate (1536 kbit/s)
    • MP2: 48 kHz sampling rate, 1 or 2 channels, up to 256 kbit/s
    • Up to 8 audio tracks containing Dolby Digital, DTS, PCM (uncompressed audio) or MPEG-1 Audio Layer II. (One audio track must have MPEG-1, Dolby Digital or PCM Audio.)
    Initially, in countries using the PAL standard (e.g. most of Europe) the sound of DVD was supposed to be standardized on PCM and MP2, but apparently against the wishes of Philips, under public pressure on December 5, 1997, the DVD Forum accepted the addition of Dolby AC-3 to the optional formats on discs and mandatory formats in players. The vast majority of commercial PAL releases now employ AC-3 audio.
    DVDs can contain more than one channel of audio to go together with the video content. In many cases, sound tracks in more than one language track are present (for example, a dubbed track in the language of the country where the disc is sold in addition to one in the film's original language).
    With several channels of audio from the DVD, the cabling needed to carry the signal to an amplifier or TV can occasionally be somewhat frustrating. Most systems include an optional digital connector for this task, which is then paired with a similar input on the amplifier. The selected audio signal is sent over the connection, typically over RCA connectors or TOSLINK, in its original format to be decoded by the audio equipment. When playing compact discs, the signal is sent in S/PDIF format instead.
    Video is another issue which continues to most present problems. Current players typically output analog video only, both composite video on an RCA jack, as well as S-Video in the standard connector. However neither of these connectors were intended to be used for progressive video, so yet another set of connectors has started to appear, to carry a form of component video, which keeps the three components of the video, one luminance signal and two color difference signal, as stored on the DVD itself, on fully separate wires (whereas S-Video uses two wires, uniting and degrading the two color signals, and composite only one, uniting and degrading all three signals). The connectors are further confused by using a number of different physical connectors on different player models, RCA or BNC, as well as using VGA cables in a non-standard way (VGA is normally analog RGB—a different, incompatible form of component video). Even worse, there are often two sets of component outputs, one carrying interlaced video, and the other progressive. In Europe (but not most other PAL areas), SCART connectors are typically used, which can carry composite, Y/C (S-Video), and/or analog RGB interlaced video signals, as well as analog two-channel sound on a single convenient multiwire cable. The analog RGB component signal offers video quality which is superior to S-Video and identical to YPbPr component video (ignoring any conversion or noise issues). However, analog RGB and S-Video signals can not be carried simultaneously, due to each using the same pins for different uses, and displays often must be manually configured as to the input signal, since no switching mode exists for S-Video. (A switching mode does exist to indicate whether composite or RGB is being used.) Some DVD players and set-top boxes offer YPbPr component video signals over the wires in the SCART connector intended for RGB, though this violates the official specification and manual configuration is again necessary. (Hypothetically, unlike RGB component, YPbPr component signals and S-Video Y/C signals could both be sent over the wire simultaneously, since they share the luminance (Y) component.) HDMI is a new digital connection similar to DVI; it carries High Definition, Enhanced Definition and Standard Definition video. Along with video HDMI also supports up to eight-channel digital audio. Some HDMI-equipped DVD players can upconvert the video to higher definition formats such as 720p and, more rarely, 1080p.
    DVD Video may also include one or more subtitle tracks in various languages, including those made especially for the deaf and hearing impaired. They are stored as bitmap images with transparent background which are overlaid over the video during playback. The subtitle track is contained within the VOB file of the DVD. Subtitles are restricted to four colors (including transparency) and thus tend to look cruder than permanent subtitles on film.
    DVD Video may contain Chapters for easy navigation (and continuation of a partially watched film). If space permits, it is also possible to include several versions (called "angles") of certain scenes, though today this feature is mostly used—if at all—not to show different angles of the action, but as part of internationalization to e.g. show different language versions of images containing written text, if subtitles will not do (for instance, credits). Multiple angles have found a niche in markets such as yoga and pornography.
    A major selling point of DVD Video is that its storage capacity allows for a wide variety of extra features in addition to the feature film itself. This can include audio commentary that is timed to the film sequence, documentary features, unused footage, trivia text commentary, simple games and film shorts.
    Other extras that can be included on DVDs (extra to the main audio/visual programme) are motion menus, still pictures, up to 32 selectable subtitles, seamless branching for multiple storylines, 9 camera angles. And also additional DVD-ROM / data files that only can be read by computer DVD drives.
    [edit]
    Restrictions
    DVD-Video has four complementary systems designed to restrict the DVD user in various ways: Macrovision, Content Scrambling System (CSS), region codes, and disabled user operations (UOPs).
    [edit]
    Content-scrambling system
    Many DVD-Video titles use content-scrambling system (CSS) encryption, which is intended to discourage people from copying the disc. Usually, users need to install software provided on the DVD or downloaded from the Internet such as WinDVD, PowerDVD, MPlayer, or VLC to be able to view the disc in a computer system.
    Without descrambling first, any digital copy of the disc will be ruined. Unplayable everywhere, including computers.
    The CSS has caused major problems for the inclusion of DVD players in any open source operating systems, since open source player implementations are not officially given access to the decryption keys or license the patents involved in the CSS. Proprietary software players were also difficult to find on some platforms. However, a successful effort has been made to write a decoder by reverse engineering, resulting in DeCSS. This has led to long-running legal battles and the arrest of some of those involved in creating or distributing the DeCSS code, through the use of the controversial U.S. Digital Millennium Copyright Act, on the grounds that such software could also be used to facilitate unauthorized copying of the data on the discs.
    These laws currently affect only the United States; most other countries can use de-scrambling software to bypass the DVD restrictions. A number of software programs have since appeared on the Web to view DVDs on a number of different platforms.
    Other measures such as RipGuard, as well as US and international copyright law, may be used to prevent making unauthorized copies of DVDs. CSS decrypting software (such as DVD Decrypter AnyDVD and DVD Shrink) allows a disc to be copied to hard disk unscrambled and (as an extra feature) region-specific DVD to be copied as an all-region DVD. It also removes Macrovision, Content Scrambling System (CSS), region codes, and disabled user operations (UOPs).
    [edit]
    Disabled user operations
    DVD-Video allows the disc to specify whether or not the user may perform any operation, such as selecting a menu, skipping chapters, forwarding or rewinding—essentially any function on the remote control. This is known as User Operation Prohibitions, or Prohibited User Operations (UOPs or PUOs). Most DVD players respect these commands (e.g. by preventing fast-forwarding through a copyright message at the beginning of a disc), although some can be configured to ignore them, particularly open source player software.
    Many grey market players ignore UOPs. Many popular DVD "reauthoring" software packages allow the user to strip out PUOs, and burn a new copy without the restrictions. While this is illegal in many countries, it is commonly argued in online forums that, having legally purchased the DVD and its content, users are ethically entitled to view 'their' content the way they prefer. Many feel that being 'forced' to watch PUO-protected content, and having functions on their playback equipment disabled, is an unfair imposition by the distributor, particularly due to the fact that PUO-protected content is almost inevitably commercial content (previews and/or advertising of other films or products).
    [edit]
    Region codes
    Main article: DVD region code


    The world defined by DVD
    Each DVD-Video disc contains one or more region codes, denoting the area of the world in which distribution and playback are intended. The commercial DVD player specification dictates that a player must only play discs that contain its region code. In theory, this allows the motion picture studios to control the various aspects of a release (including content, date and price) on a region-by-region basis. In practice, many DVD players allow playback of any disc, or can be modified to do so. Entirely independent of encryption, region coding pertains to regional lockout, which originated in the video game industry.
    From a worldwide perspective, regional coding has been a failure. A huge percentage of players outside of North America can be easily modified (and are even sold pre-modified by mainstream stores such as Amazon.co.uk) to ignore the regional codes on a disc. This, coupled with the fact that almost all televisions in Europe and Australasia are capable of displaying NTSC video, means that consumers in these regions have a huge choice of discs. Contrary to popular belief, this practice is not illegal and in some territories that strongly support free trade (Australia being the best example) it is encouraged.
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    DVD-Audio
    Main article: DVD-Audio
    DVD-Audio is a format for delivering high-fidelity audio content on a DVD. It offers many channel configuration options (from mono to 5.1 surround sound) at various sampling frequencies and sample rates. Compared with the CD format, the much higher capacity DVD format enables the inclusion of either considerably more music (with respect to total running time and quantity of songs) or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, and/or additional channels for spatial sound reproduction).
    Despite DVD-Audio's superior technical specifications, there is debate as to whether or not the resulting audio enhancements are distinguishable to typical human ears. DVD-Audio currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment.
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    Security
    Main article: CPRM
    DVD-Audio discs employ a robust copy prevention mechanism, called Content Protection for Prerecorded Media (CPPM) developed by the 4C group (IBM, Intel, Matsushita, and Toshiba).
    CPPM can be circumvented on a PC by capturing decoded audio streams in PCM format, but the underlying protection mechanism, encryption algorithms, and keys have not yet been cracked.
    [edit]
    Players and recorders
    Modern DVD recorders often support additional formats, including DVD+/-R/RW, CD-R/RW, MP3, WMA, SVCD, JPEG, PNG, SVG, KAR and MPEG-4 (DivX/XviD). Some also include USB ports or flash memory readers. Many players are priced from under $/€ 25 and recorders from $/€ 50.
    DVD drives for computers usually come with one of two kinds of Regional Playback Control (RPC), either RPC-1 or RPC-2; This is used to enforce the publisher's restrictions on what regions of the world the DVD can be played. See Regional lockout.
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    Competitors and successors
    There are several possible successors to DVD being developed by different consortiums: Sony/Panasonic's Blu-ray Disc (BD), Toshiba's HD DVD and Maxell's Holographic Versatile Disc (HVD).
    The first generation of holographic media with 300 GB of storage capacity and a 160 Mbit/s transfer rate is scheduled for release in late 2006 by Maxell and its partner, InPhase.
    On November 18, 2003, the Chinese news agency Xinhua reported the final standard of the Chinese government-sponsored Enhanced Versatile Disc (EVD), and several patents for it. However, since then the format has generally failed to live up to expectations.
    On November 19, 2003, the DVD Forum decided by a vote of eight to six that HD DVD will be its official HDTV successor to DVD. This had no effect on the competing Blu-ray Disc Association's (BDA) determination that its format would succeed DVD, especially since most of the voters belonged to both groups.
    On April 15, 2004, in a co-op project with TOPPAN Printing Co., the electronics giant Sony Corp. successfully developed the paper disc, a storage medium that is made out of 51% paper and offers up to 25 GB of storage, about five times more than the standard 4.7 GB DVD. The disc can be easily cut with scissors and recycled, offering foolproof data security and an environment-friendly storage media.
    As reported in a summer, 2005, issue of Popular Mechanics, it is not yet clear which technology will win the format war over DVD. HD DVD discs have a lower capacity than Blu-ray discs (15 GB vs. 25 GB for single layer, 30 GB vs. 50 GB for dual layer), but Blu-ray requires changes in manufacturing machinery and techniques and is thus more expensive.
    In April, 2000, Sonic Solutions and Ravisent announced hDVD, an HDTV extension to DVD that presaged the HD formats that debuted 6 years later. [3]
    This situation—multiple new formats fighting as the successor to a format approaching purported obsolescence—previously appeared as the "war of the speeds" in the record industry of the 1950s; see gramophone record for details of that situation. It is also, of course, similar to the VHS/Betamax war in consumer video recorders in the late 1970s.
    It is possible that neither Blu-ray, HD DVD, nor a next-generation optical recording products will succeed. The storage capacities of hard disk drives and solid-state memory have grown faster than those of optical discs (since CD's introduction year, 1983, storage capacity of HDDs grew by a factor of about 100,000, from 5 MB to 500 GB, while the capacity of Blu-ray is only 90 times larger than CD), and all three are much more capable of storing general consumer content —such as photos, music, and video— than in the past. Hard disk drives having a few terabytes of storage capacity will be on the market before 2008. A terabyte is equivalent to about 2000 CD-ROMs, 130 DVD-9s, or 20 dual-layer BDs. However, hard disk drives and memory cards are at the moment hundreds of times more expensive than optical discs (US$50 or more compared to $0.50), so they will never replace discs as a publishing format. The price per gigabyte of a hard disk drive, $0.40 ($200/500 GB), is growing closer to that of a DVD-ROM, $0.06 ($0.50/8.5 GB), or BD-ROM, $0.03 ($1.50/50 GB), or recordable DVD-5, $0.10 ($0.50/4.7 GB), and is lower than the cost of a recordable DVD-9, $0.30 ($2.50/8.5 GB), or BD-RE25, $1.20 ($30/25 GB). Direct access to large amounts of information is much more convenient with a hard disk drive. As broadband becomes fast enough (40 Mbit/s and higher) and more widely available, physical media will become less important as a distribution format.
    One last possibility is that DVD will not be replaced in terms of Home Theatre by any format currently developed. People may not be so keen to upgrade their DVD collection so (relatively) soon. DVD may remain the format of choice for many more years, which may lead to the creation of a better technology that will replace it.
    The new generations of optical formats have restricted access (anti-copy mechanisms), and it is therefore possible that consumers will ignore them as they did with Super Audio CD.
    [edit]
    Direct-to-DVD
    The popularity of DVDs has caused the term "direct-to-DVD" to widely replace "Direct-to-video" (see main article). However, the lucrative market for DVDs has resulted in less stigma for direct-to-DVD releases as compared to direct-to-video releases. Some minor films can be made with a small budget and turn a profit on DVD sales alone, and some are made specifically for this purpose.

































    Compact Disc
    From Wikipedia, the free encyclopedia
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    "CD" redirects here. For other uses, see CD (disambiguation). For the Public Image Ltd album called "Compact Disc" on certain editions, see Album (album).


    The Compact Disc logo was inspired by that of the previous Compact Cassette. It may only be used on discs that comply with the Red Book specifications
    A Compact Disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. The CD, introduced in 1982, remains the standard playback format for commercial audio recordings as of mid-2006. An audio compact disc consists of one or more stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Standard compact discs have a diameter of 120 mm or 80 mm. The 120 mm discs can hold approximately 80 minutes of audio. The 80 mm discs, sometimes used for CD singles, hold approximately 20 minutes of audio. Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM, and to include record-once and re-writable media (CD-R and CD-RW). CD-ROMs and CD-Rs remain widely used technologies in the personal-computer industry as of 2006. The CD and its extensions have been extremely successful: in 2004, the annual worldwide sales of CD-Audio, CD-ROM, and CD-R reached about 30 billion discs.
    Contents
    [hide]
    • 1 History
    • 2 Physical details
    • 3 Disc shapes and diameters
    • 4 Audio format
    o 4.1 Storage capacity and playing time
    o 4.2 Main physical parameters
    o 4.3 Data structure
    • 5 CD-ROM
    • 6 Manufacture
    • 7 Recordable CD
    • 8 Copy protection
    • 9 References
    • 10 See also

    [edit]
    History
    In the early 1970s, using video Laserdisc technology, Philips' researchers started experiments with "audio-only" optical discs, initially with wideband frequency modulation FM and later with digitized PCM audio signals. The compact disc was thus developed by Philips from its own 12 inch Philips LaserVision discs. At the end of the 1970s, Philips, Sony, and other companies presented prototypes of digital audio discs.
    In 1979 Philips and Sony decided to join forces, setting up a joint task force of engineers whose mission was to design the new digital audio disc. Prominent members of the task force were Kees Immink and Toshitada Doi. After a year of experimentation and discussion, the taskforce produced the "Red Book", the Compact Disc standard. Philips contributed the general manufacturing process, based on the video LaserDisc technology. Philips also contributed the Eight-to-Fourteen Modulation, EFM, which offers both a long playing time and a high resilience against disc handling damage such as scratches and fingerprints; while Sony contributed the error-correction method, CIRC. The Compact Disc Story, told by a former member of the taskforce, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. According to Philips, the Compact Disc was thus "invented collectively by a large group of people working as a team."[1]
    The Compact Disc reached the market in late 1982 in Asia and early the following year in other markets. This event is often seen as the "Big Bang" of the digital audio revolution. The new audio disc was enthusiastically received, especially in the early-adopting classical music and audiophile communities and its handling quality received particular praise. The far larger popular and rock music industries were slower to adopt the new format, especially in the huge consumer markets in Europe and the United States.
    The design of the CD was originally conceived as an evolution of the gramophone record, rather than primarily as a data storage medium. Only later did the concept of an 'audio file' arise, and the generalising of this to any data file. From its origins as a music format, Compact Disc has grown to encompass other applications. In June 1985, the CD-ROM (read-only memory) and, in 1990, CD-Recordable were introduced, also Developed by Sony and Philips.
    [edit]
    Physical details

    Compact discs are made from a 1.2 mm thick disc of very pure polycarbonate plastic. A thin layer of Super Purity Aluminium is applied (or rarely gold, used for its data longevity, such as in some limited-edition audiophile CDs) to the surface to make it reflective, which is protected by a film of lacquer. The lacquer can be printed with a label. Common printing methods for compact discs are silkscreening and offset printing. CD data is stored as a series of tiny indentations (pits), encoded in a tightly packed spiral track of pits moulded into the top of the polycarbonate layer. The areas between pits are known as 'lands'. Each pit is approximately 100 nm deep by 500 nm wide, and varies from 850 nm to 3.5 μm of length. The spacing between the tracks, the pitch, is 1.6 μm. A CD is read by focusing a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The difference in height between pits and lands leads to a phase difference between the light reflected from a pit and from its surrounding land. By measuring the intensity with a photodiode, one is able to read the data from the disc. The pits and lands themselves do not represent the zeroes and ones of binary data. Instead a change from pit to land or land to pit indicates a one, while no change indicates a zero. This in turn is decoded by reversing the Eight-to-Fourteen Modulation used in mastering the disc, and then reversing the Cross-Interleaved Reed-Solomon Coding, finally revealing the raw audio data stored on the disc.


    A Mini-CD is 8 centimeters in diameter
    The Red Book specifies many mechanical parameters including the pit depth. It specifies that the pit depth should be less than (and, thus, not equal to) 130 nm. However, the Red Book implicitly specifies the pit depth by specifying the strength of both the push-pull radial tracking signal and full aperture detection signal. For a maximum full aperture signal, the optimum pit depth is λ/4n = 130 nm (refractive index n=1.5, λ=780 nm). For a maximum push-pull radial tracking signal the best choice is λ/8n = 65 nm. Most CD manufacturers, dependent on the exact pit geometry such as the slope of the pit edges etc, choose a pit depth of around 90-100 nm, (which is around λ/6n) yielding a sound trade-off between the quality of the push-pull radial tracking and full aperture detection signal.
    Pits are much closer to the label side of a disc so that defects and dirt on the clear side can be out of focus during playback. Discs consequently suffer more damage because of defects such as scratches on the label side, whereas clear-side scratches can be repaired by refilling them with plastic of similar index of refraction.
    [edit]
    Disc shapes and diameters
    In reverse fashion to that of a vinyl record, the digital data on a CD begins at the center of the disc and proceeds outwards to the edge, which allows adaptation to the different size formats available. Standard CDs are available in two sizes. By far the most common is 120 mm in diameter, with a 74-minute audio capacity and a 650 MB data or an 80-minute audio capacity and a 700 MB data. 80mm discs are also available, a format which is mainly used for audio CD singles in some regions (e.g. Japan), much like the old vinyl single. Each such "miniCD" or "Maxi CD" can hold 21 minutes of music, or 184 MB of data (this form factor has also been called "CD3", since it is about three inches across). There is a 15 mm hole in the centre of the disc, usually used by some form of clamp or clip device within the player to hold it in place and allow it to be rotated by a motor.
    Other non-standard shapes and smaller form factors have also been sold or given away as promotional items. All of these unique shapes must fit within the 120mm ring or the 80mm ring that is standard on tray drives. Any shape falling between the 80mm ring and the 120mm ring of a tray drive, such as a credit card-sized CD business cards, must include a method of locating the disc in the tray during load and unload. This is usually a circular ridge on their underside. Irregularly shaped, non rotationally symmetric discs with an offset centre of mass may cause damaging vibration if played in computer CD drives, which may operate at a much higher rotational velocity than stand-alone audio CD players. Even symmetrical rectangular discs often cause far more vibration than standard circular ones.
    [edit]
    Audio format
    The format of the audio disc, known as the "Red Book" standard, was laid out by Sony and Philips in 1981. The format is a two-channel 16-bit PCM encoding at a 44.1 kHz sampling rate. Four-channel sound is an allowed option within the Red Book format, but has never been implemented.
    The sampling rate of 44.1 kHz is inherited from a method of converting digital audio into an analog video signal for storage on video tape, which was the most affordable way to get the data from the recording studio to the CD manufacturer at the time the CD specification was being developed. A device that turns an analog audio signal into PCM audio, which in turn is changed into an analog video signal is called a PCM adaptor. This technology could store six samples (three samples per each stereo channel) in a single horizontal line. A standard NTSC video signal has 245 usable lines per field, and 59.94 fields/s, which works out at 44,056 samples/s. Similarly PAL has 294 lines and 50 fields, which gives 44,100 samples/s. This system could either store 14-bit samples with some error correction, or 16-bit samples with almost no error correction. There was a long debate over whether to use 14 or 16 bit samples and/or 44,056 or 44,100 samples/s when the Sony/Philips task force designed the compact disc; 16 bits and 44.1 kilosamples per second prevailed.
    [edit]
    Storage capacity and playing time
    The original target storage capacity for a CD was one hour of audio content, and a disc diameter of 11.5 cm was sufficient. However, according to Philips, Sony vice-president Norio Ohga suggested extending the capacity to 74 minutes to accommodate a complete performance of Beethoven's 9th Symphony on a single disk.[2] Kees Immink of Philips refutes this.[3] The extra playing time required changing to a 12 cm disc.
    According to a Sunday Tribune interview [4] the story is slightly more involved. At that time (1979) Philips owned Polygram, one of the world's largest distributors of music. Polygram had set up a large experimental CD disc plant in Hanover, Germany, which could produce huge amounts of CDs having, of course, a diameter of 11.5cm. Sony did not yet have such a facility. If Sony had agreed on the 11.5cm disc, Philips would have had a significant competitive edge in the market. Sony was aware of that, did not like it, and something had to be done. The long-playing time of Beethoven's Ninth imposed by Ohga was used to push Philips to accept 12cm, so that Philips' Polygram lost its edge on disc fabrication.
    The 74-minute playing time of a CD, being more than that of most long-playing vinyl albums, was often used to the format's advantage during the early years when CDs and LPs vied for commercial sales. CDs would often be released with one or more bonus tracks, enticing consumers to buy the CD for the extra material. However, attempts to combine double LPs onto one CD occasionally resulted in an opposing situation in which the CD would actually offer fewer tracks than the LP equivalent.
    [edit]
    Main physical parameters
    The main parameters of the CD (taken from the September 1983 issue of the compact disc specification) are as follows:
    • Scanning velocity: 1.2–1.4 m/s (constant linear velocity) - equivalent to approximately 500 rpm at the inside of the disc, and approximately 200 rpm at the outside edge.
    • Track pitch: 1.6 μm.
    • Disc diameter 120 mm.
    • Disc thickness: 1.2 mm.
    • Inner radius program area: 25 mm.
    • Outer radius program area: 58 mm.
    The program area is 86.05 cm², so that the length of the recordable spiral is 86.05/1.6 = 5.38 km. With a scanning speed of 1.2 m/s, the playing time is 74 minutes, or around 650 MB of data on a CD-ROM. If the disc diameter were 115 mm, the maximum playing time would have been 68 minutes, i.e., six minutes less. A disc with data appearing slightly more densely is tolerated by most players (though some old ones fail). Using a linear velocity of 1.2 m/s and a track pitch of 1.5 micrometre leads to a playing time of 80 minutes, or a capacity of 700 MB. Even higher capacities on non-standard discs (up to 99 minutes) are available at least as recordables, but generally the tighter the tracks are squeezed the worse the compatibility with will be.
    [edit]
    Data structure
    The smallest entity in the CD audio format is called a frame. A frame can accommodate six complete 16-bit stereo samples, i.e. 2×2×6 = 24 bytes. A frame comprises 33 bytes, of which 24 are audio bytes (six full stereo samples), eight CIRC-generated error correction bytes, and one subcode byte. The eight bits of a subcode byte are available for control and display. Under Eight-to-Fourteen Modulation (EFM) rules, each data/audio byte is translated into 14-bit EFM words, which alternates with 3-bit merging words. In total we have 33*(14+3) = 561 bits. A 27-bit unique synchronization word is added, so that the number of bits in a frame totals 588. The synchronization word cannot occur in the normal bit stream, and can thus be used to identify the beginning of a frame. Data in a CD-ROM are organized in both frames and sectors, where a CD-ROM sector contains 98 frames, and holds 98×24 = 2352 (user) bytes.
    [edit]
    CD-ROM
    Main article: CD-ROM
    For its first few years of existence, the compact disc was purely an audio format. However, in 1985 Yellow Book CD-ROM standard was established by Sony and Philips, which defined a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM (CDR) drive.
    [edit]
    Manufacture
    Main article: CD manufacturing
    Pre-pressed CDs are mass-produced by a process of stamping, where a glass master disc is created and used to make "stampers", which in turn are used to manufacture multiple copies of the final disc with the pits already present.
    [edit]
    Recordable CD
    Main article: CD-R


    A typical 700-megabyte CD-R
    Recordable compact discs, CD-Rs, are injection molded with a "blank" data spiral. A photosensitive dye is then applied, and then the discs are metallized and lacquer coated. The write laser of the CD recorder changes the color of the dye to allow the read laser of a standard CD player to see the data as it would an injection molded compact disc. CD-R recordings are permanent. The resulting discs can be read by most CD-ROM drives and played in most audio CD players.
    CD-RW is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser in this case is used to heat and alter the chemical properties of the alloy and hence change its reflectivity. A CD-RW does not have as great a difference in the reflectivity of lands and bumps as a pressed CD or a CD-R, and so many CD audio players cannot read CD-RW discs, although the majority of stand-alone DVD players can.
    [edit]
    Copy protection
    Main article: CD/DVD copy protection
    The Red Book audio specification, except a simple 'anti-copy' bit in the subcode, does not include any serious copy protection mechanism. Starting in early 2002, attempts were made by record companies to market "copy-protected" non-standard compact discs. Philips has stated that such discs are not permitted to bear the trademarked Compact Disc Digital Audio logo because they violate the Red Book specification. However, there has been great public outcry over copy-protected discs because many see it as a threat to fair use.
    [edit]
    References
    • Kees Immink, The Compact Disc Story, Journal of the Audio Engineering Society, 46(5), pp. 458-465, May 1998.
    • Kenneth C. Pohlmann (1992). The Compact Disc Handbook. Middleton, Wisconsin: A-R Editions. ISBN 895793008.
    • Sony's official CD history
    Data Storage: DVD vs. CD
    DVDs can store more data than CDs for a few reasons:
    • Higher-density data storage
    • Less overhead, more area
    • Multi-layer storage
    Higher Density Data Storage
    Single-sided, single-layer DVDs can store about seven times more data than CDs. A large part of this increase comes from the pits and tracks being smaller on DVDs.
    Specification CD DVD
    Track Pitch 1600 nanometers 740 nanometers
    Minimum Pit Length
    (single-layer DVD) 830 nanometers
    </FONT< td> 400 nanometers
    Minimum Pit Length
    (double-layer DVD) 830 nanometers 440 nanometers
    Let's try to get an idea of how much more data can be stored due to the physically tighter spacing of pits on a DVD. The track pitch on a DVD is 2.16 times smaller, and the minimum pit length for a single-layer DVD is 2.08 times smaller than on a CD. By multiplying these two numbers, we find that there is room for about 4.5 times as many pits on a DVD. So where does the rest of the increase come from?
    Less Overhead, More Area
    On a CD, there is a lot of extra information encoded on the disc to allow for error correction -- this information is really just a repetition of information that is already on the disc. The error correction scheme that a CD uses is quite old and inefficient compared to the method used on DVDs. The DVD format doesn't waste as much space on error correction, enabling it to store much more real information. Another way that DVDs achieve higher capacity is by encoding data onto a slightly larger area of the disc than is done on a CD.
    Multi-Layer Storage
    To increase the storage capacity even more, a DVD can have up to four layers, two on each side. The laser that reads the disc can actually focus on the second layer through the first layer. Here is a list of the capacities of different forms of DVDs:
    Format Capacity Approx. Movie Time
    Single-sided/single-layer 4.38 GB 2 hours
    Single-sided/double-layer 7.95 GB 4 hours
    Double-sided/single-layer 8.75 GB 4.5 hours
    Double-sided/double-layer 15.9 GB Over 8 hours
    You may be wondering why the capacity of a DVD doesn't double when you add a whole second layer to the disc. This is because when a disc is made with two layers, the pits have to be a little longer, on both layers, than when a single layer is used. This helps to avoid interference between the layers, which would cause errors when the disc is played.

    The DVD Video Format
    DVD Fact
    If an average DVD movie were uncompressed, it would take at least a year to download it over a normal phone line.
    Even though its storage capacity is huge, the uncompressed video data of a full-length movie would never fit on a DVD. In order to fit a movie on a DVD, you need video compression. A group called the Moving Picture Experts Group (MPEG) establishes the standards for compressing moving pictures.
    When movies are put onto DVDs, they are encoded in MPEG-2 format and then stored on the disc. This compression format is a widely accepted international standard. Your DVD player contains an MPEG-2 decoder, which can uncompress this data as quickly as you can watch it.
    The MPEG-2 Format and Data Size Reduction
    A movie is usually filmed at a rate of 24 frames per second. This means that every second, there are 24 complete images displayed on the movie screen. American and Japanese television use a format called NTSC, which displays a total of 30 frames per second; but it does this in a sequence of 60 fields, each of which contains alternating lines of the picture. Other countries use PAL format, which displays at 50 fields per second, but at a higher resolution (see How Video Formatting Works for details on these formats). Because of the differences in frame rate and resolution, an MPEG movie needs to be formatted for either the NTSC or the PAL system.
    The MPEG encoder that creates the compressed movie file analyzes each frame and decides how to encode it. The compression uses some of the same technology as still image compression does to eliminate redundant or irrelevant data. It also uses information from other frames to reduce the overall size of the file. Each frame can be encoded in one of three ways:
    • As an intraframe - An intraframe contains the complete image data for that frame. This method of encoding provides the least compression.
    • As a predicted frame - A predicted frame contains just enough information to tell the DVD player how to display the frame based on the most recently displayed intraframe or predicted frame. This means that the frame contains only the data that relates to how the picture has changed from the previous frame.
    • As a bidirectional frame - In order to display this type of frame, the player must have the information from the surrounding intraframe or predicted frames. Using data from the closest surrounding frames, it uses interpolation (something like averaging) to calculate the position and color of each pixel.
    Did you know?
    DVDs often have special features hidden on the disc. These "Easter eggs" can be previews of other movies, computer software or music. DVD Review has a listing of some great Easter eggs that viewers have found on DVDs.

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