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Transport systems [edit]

Two transport systems evolved in the early video machines, known as the alpha wrapand

the omega wrap. In thealphawrap machines the tape was wrapped around the head drum for a full

360 degrees (the tape looking like the lowercase Greek letter alpha). There was only one head which

wrote a complete stripe for every revolution of the head. This system had problems when the headtransited from one piece of tape to the next giving a large signal gap between fields. The machine had

to fill this gap with the frame synchronizing pulses. Such machines were constrained to using guard

band recording (see below).

In theomegawrap machines, the tape was only wrapped around the head for 180 degrees. Two

video heads were required, each writing alternate fields. This system had a much smaller signal gap

between fields, but the frame synchronizing pulses were able to be recorded on the tape. Cassette

based systems could only utilize the omega wrap technique, since it was geometrically impossible for

an automatic loading system to introduce a loop into the tape. Early omega wrap systems utilized

guard band recording, but the presence of two heads permitted the development of the slant azimuth

technique. Later developments used increasing numbers of heads to record video using smaller

drums and for recordingHiFisound as well.

A variation of the omega wrap, such as that used by Echo Science Corporation of Mountain View,

California in its instrumentation and high resolution video recorders in the late 1970s and 1980s,

wrapped the 1-inch tape about 190 degrees around the two-headed drum, so there was signal

overlap between the two heads. Head switching in video recorders occurred instantaneously in the

video models, during an horizontal sync interval. With a standard NTSC video signal a head could

cover one-sixth of a field each time it passed across the tape. Switching in instrumentation models

was gradual, so the signals from both heads overlapped briefly, producing a transient-free output

signal where the original signal did not contain convenient dead intervals during which a switching

transient could be hidden.
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Direct-broadcast satelliteFrom Wikipedia, the free encyclopedia


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This article needs additional citations for verification. Please helpimprove

this articlebyadding citations to reliable sources.Unsourced material may

bechallengedandremoved.(May 2012)

For the Japanese communication satellites, seeBroadcasting Satellite (Japanese).

A DTH dish antenna mounted on wall

Direct broadcast satellite(DBS) is a term used to refer to satellite televisionbroadcasts intended for

home reception.

A designation broader than DBS would be direct-to-homesignals, or DTH. This has initially distinguished

the transmissions directly intended for home viewers from cable television distribution services that

sometimes carried on the same satellite. The term DTH predates DBS and is often used in reference to

services carried by lower power satellites which required largerdishes(1.7m diameter or greater) for

reception.

In Europe, prior to the launch ofAstra 1Ain 1988, the term DBS was commonly used to describe the

nationally commissioned satellites planned and launched to provide TV broadcasts to the home within

several European countries (e.g.BSBin the UK, TV-Sat in Germany). These services were to use the D-

Mac and D2-Macformat and BSS frequencies with circularpolarizationfrom orbital positions allocated to

each country. Before these DBS satellites, home satellite television in Europe was limited to a few

channels, really intended for cable distribution, and requiring dishes typically of 1.2m.SESlaunched theAstra 1A satellite to provide services to homes across Europe receivable on dishes of just 60 cm-80 cm

and, although these mostly used PAL video format and FSS frequencies with linear polarization, the DBS

name slowly came to applied to all Astra satellites and services too.

IPTVFrom Wikipedia, the free encyclopedia

This article is about Internet Protocol Television. For public television broadcasting in Iowa, seeIowa Public

Television.
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Internet Protocol television(IPTV) is a system through whichtelevisionservices are delivered using

theInternet protocol suiteover apacket-switched networksuch as theInternet,instead of being delivered

through traditionalterrestrial,satellitesignal, andcabletelevision formats.

IPTV services may be classified into three main groups:

live television,with or without interactivity related to the current TV show;

time-shiftedtelevision: catch-up TV (replays a TV show that was broadcast hours or days ago), start-

over TV (replays the current TV show from its beginning);

video on demand(VOD): browse a catalog of videos, not related to TV programming.

IPTV is distinguished fromInternet televisionby its on-going standardization process (e.g.,European

Telecommunications Standards Institute)and preferential deployment scenarios in subscriber-based

telecommunications networks with high-speed access channels into end-user premises viaset-top

boxesor othercustomer-premises equipment.

Definition [edit]

Historically, many different definitions of IPTV have appeared, including elementary streams over IP

networks, transport streams over IP networks and a number of proprietary systems.

One official definition approved by theInternational Telecommunication Unionfocus group on IPTV

(ITU-T FG IPTV) is:

"IPTV is defined as multimedia services such as television/video/audio/text/graphics/data delivered

over IP based networks managed to provide the required level of quality of service and experience,

security, interactivity and reliability."[1]

Another more detailed definition of IPTV is the one given byAlliance for Telecommunications Industry

Solutions(ATIS) IPTV Exploratory Group on 2005:

"IPTV is defined as the secure and reliable delivery to subscribers of entertainment video and related

services. These services may include, for example, Live TV, Video On Demand (VOD) andInteractive

TV (iTV).These services are delivered across an access agnostic, packet switched network that

employs the IP protocol to transport the audio, video and control signals. In contrast to video over the

public Internet, with IPTV deployments, network security and performance are tightly managed to

ensure a superior entertainment experience, resulting in a compelling business environment for

content providers, advertisers and customers alike."[2]

Compact discFrom Wikipedia, the free encyclopedia

"CD" redirects here. For other uses, seeCD (disambiguation).

This article is about the optical disc. For the Hungarian band, see Compact Disco.
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Compact disc

The readable surface of a Compact disc includes a spiral track wound

tightly enough to cause light todiffractinto a fullvisible spectrum

Media type Optical disc

Encoding Various

Capacity Typically up to 700MiB(up to 80 minutes audio)

Read mechanism 780nmwavelength (infraredandrededge)

semiconductor laser, 1200Kib/s (1)

Write mechanism 1200 Kib/s (1)

Developed by Philips, Sony

Usage Audio and data storage

Optical discs

General[show]

Optical media types[show]
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Standards[show]

See also[show]

V

T

E

The compact disc, or CDfor short, is anoptical discused to storedigital data,and was originally

developed to store and play back sound recordings only. The format was later adapted for storage of

data (CD-ROM), write-once audio and data storage (CD-R), rewritable media (CD-RW), Video

Compact Disc (VCD), Super Video Compact Disc (SVCD), PhotoCD, PictureCD, CD-i, andEnhanced

CD.Audio CDs and audioCD playershave been commercially available since October 1982.

Standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to 80 minutes of

uncompressed audio or 700MiB(actually about 703 MiB or 737MB)of data. TheMini CDhas various

diameters ranging from 60 to 80 millimetres (2.4 to 3.1 in); they are sometimes used for CD singles,

storing up to 24 minutes of audio or deliveringdevice drivers.

At the time of the technology's introduction it had more capacity than computerhard drivescommon at

the time. The reverse is now true, with hard drives far exceeding the capacity of CDs.

In 2004, worldwide sales of CD audio, CD-ROM, and CD-R reached about 30 billion discs. By 2007,

200 billion CDs had been sold worldwide.[1]Compact discs are increasingly being replaced or

supplemented by other forms of digital distribution and storage, such as downloading and flash drives,

with audio CD sales dropping nearly 50% from their peak in 2000 .[2]

Physical details [edit]
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Diagram of CD layers.

A. A polycarbonate disc layer has the data encoded by using bumps.

B. A shiny layer reflects the laser.C. A layer of lacquer protects the shiny layer.

D. Artwork isscreen printedon the top of the disc.

E. A laser beam reads the CD and is reflected back to a sensor, which converts it into electronic data

A CD is made from 1.2 millimetres (0.047 in) thick,polycarbonateplastic and weighs 15

20 grams.[25]

From the center outward, components are: the center spindle hole (15 mm), the first-

transition area (clamping ring), the clamping area (stacking ring), the second-transition area (mirror

band), the program (data) area, and the rim. The inner program area occupies a radius from 25 to

58 mm.

A thin layer of aluminium or, more rarely, gold is applied to the surface making it reflective. The metalis protected by a film of lacquer normallyspin coateddirectly on the reflective layer. The label is

printed on the lacquer layer, usually byscreen printingoroffset printing.

CD data is represented as tiny indentations known as "pits", encoded in a spiral track moulded into

the top of the polycarbonate layer. The areas between pits are known as "lands". Each pit is

approximately 100nmdeep by 500 nm wide, and varies from 850 nm to 3.5min length. The

distance between the tracks, the pitch, is 1.6 m.

Scanning velocity is 1.21.4 m/s (constant linear velocity)equivalent to approximately 500 rpm at

the inside of the disc, and approximately 200 rpm at the outside edge. (A disc played from beginning

to end slows down during playback.)

Comparison of various optical storage media

The program area is 86.05 cm2and the length of the recordable spiral is

(86.05 cm2/ 1.6 m) = 5.38 km. With a scanning speed of 1.2 m/s, the playing time is 74 minutes, or

650 MB of data on a CD-ROM. A disc with data packed 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 m

yields a playing time of 80 minutes, or a data 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.[citation needed]
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The pits in a CD are 500nmwide, between 830 nm and 3,000 nm long and 150 nm deep

A CD is read by focusing a 780 nmwavelength(near infrared)semiconductor laserthrough the

bottom of the polycarbonate layer. The change in height between pits and lands results in a difference

in the way the light is reflected. By measuring the intensity change with aphotodiode,the data can be

read from the disc.

The pits and lands themselves do not directly represent the zeros and ones ofbinary data.

Instead,non-return-to-zero, invertedencoding is used: a change from pit to land or land to pit

indicates a one, while no change indicates a series of zeros. There must be at least two and no more

than ten zeros between each one, which is defined by the length of the pit. This in turn is decoded by

reversing theeight-to-fourteen modulationused in mastering the disc, and then reversing theCross-

Interleaved Reed-Solomon Coding,finally revealing the raw data stored on the disc.

Integrity [edit]

CDs are susceptible to damage from both normal use[contradictory]and environmental exposure. Pits are

much closer to the label side of a disc, enabling defects and contaminants on the clear side to be outof focus during playback. Consequently, CDs are more likely to suffer damage on the label side of the

disc. Scratches on the clear side can be repaired by refilling them with similar refractive plastic, or by

careful polishing.

Disc shapes and diameters [edit]
http://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Nanometrehttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Near_infraredhttp://en.wikipedia.org/wiki/Near_infraredhttp://en.wikipedia.org/wiki/Near_infraredhttp://en.wikipedia.org/wiki/Semiconductor_laserhttp://en.wikipedia.org/wiki/Semiconductor_laserhttp://en.wikipedia.org/wiki/Semiconductor_laserhttp://en.wikipedia.org/wiki/Photodiodehttp://en.wikipedia.org/wiki/Photodiodehttp://en.wikipedia.org/wiki/Binary_datahttp://en.wikipedia.org/wiki/Binary_datahttp://en.wikipedia.org/wiki/Binary_datahttp://en.wikipedia.org/wiki/Non-return-to-zero,_invertedhttp://en.wikipedia.org/wiki/Non-return-to-zero,_invertedhttp://en.wikipedia.org/wiki/Non-return-to-zero,_invertedhttp://en.wikipedia.org/wiki/Eight-to-fourteen_modulationhttp://en.wikipedia.org/wiki/Eight-to-fourteen_modulationhttp://en.wikipedia.org/wiki/Eight-to-fourteen_modulationhttp://en.wikipedia.org/wiki/Cross-Interleaved_Reed-Solomon_Codinghttp://en.wikipedia.org/wiki/Cross-Interleaved_Reed-Solomon_Codinghttp://en.wikipedia.org/wiki/Cross-Interleaved_Reed-Solomon_Codinghttp://en.wikipedia.org/wiki/Cross-Interleaved_Reed-Solomon_Codinghttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=7http://en.wikipedia.org/wiki/Optical_media_preservationhttp://en.wikipedia.org/wiki/Optical_media_preservationhttp://en.wikipedia.org/wiki/Optical_media_preservationhttp://en.wikipedia.org/wiki/Optical_media_preservationhttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=8http://en.wikipedia.org/wiki/File:Comparison_disk_storage.svghttp://en.wikipedia.org/wiki/File:CDRomPits.jpghttp://en.wikipedia.org/wiki/File:CDRomPits.jpghttp://en.wikipedia.org/wiki/File:Comparison_disk_storage.svghttp://en.wikipedia.org/wiki/File:CDRomPits.jpghttp://en.wikipedia.org/wiki/File:CDRomPits.jpghttp://en.wikipedia.org/wiki/File:Comparison_disk_storage.svghttp://en.wikipedia.org/wiki/File:CDRomPits.jpghttp://en.wikipedia.org/wiki/File:CDRomPits.jpghttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=8http://en.wikipedia.org/wiki/Optical_media_preservationhttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=7http://en.wikipedia.org/wiki/Cross-Interleaved_Reed-Solomon_Codinghttp://en.wikipedia.org/wiki/Cross-Interleaved_Reed-Solomon_Codinghttp://en.wikipedia.org/wiki/Eight-to-fourteen_modulationhttp://en.wikipedia.org/wiki/Non-return-to-zero,_invertedhttp://en.wikipedia.org/wiki/Binary_datahttp://en.wikipedia.org/wiki/Photodiodehttp://en.wikipedia.org/wiki/Semiconductor_laserhttp://en.wikipedia.org/wiki/Near_infraredhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Nanometre


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Comparison of several forms of disk storage showing tracks (not-to-scale); green denotes start and red denotes end.

* Some CD-R(W) and DVD-R(W)/DVD+R(W) recorders operate in ZCLV, CAA or CAV modes.

The digital data on a CD begins at the center of the disc and proceeds toward 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 millimetres (4.7 in) in diameter, with a 74- or 80-minute audio capacity and a 650

or 700 MB (737,280,000 bytes) data capacity. This capacity was reportedly specified by Sony

executiveNorio Ohgaso as to be able to contain the entirety ofLondon Philharmonic Orchestra's

recording ofBeethoven's Ninth Symphonyon one disc.[8]

This diameter has been adopted by

subsequent formats, includingSuper Audio CD,DVD,HD DVD,andBlu-ray Disc.80 mm discs ("Mini

CDs") were originally designed for CDsinglesand can hold up to 24 minutes of music or 210 MB of

data but never became popular.[citation needed]Today, nearly every single is released on a 120 mm CD,

called aMaxi single.[citation needed]

Novelty CDs are also available in numerous shapes and sizes, and are used chiefly for marketing. A

common variant is the "business card" CD, a single with portions removed at the top and bottom

making the disk resemble a business card.

Physical size Audio Capacity CD-ROM Data Capacity Definition

120 mm 7499 min 650870MB Standard size

80 mm 2124 min 185210 MB Mini-CD size

80x54 mm - 80x64 mm ~6 min 10-65 MB "Business card" size

Logical formats [edit]

Audio CD [edit]

Main article:Compact Disc Digital Audio

The logical format of an audio CD (officially Compact Disc Digital Audio or CD-DA) is described in adocument produced by the format's joint creators, Sony and Philips in 1980. The document is known

colloquially as the Red BookCD-DAafter the color of its cover. The format is a two-channel 16-

bitPCMencoding at a44.1 kHzsampling rateper channel.Four-channel soundwas to be an

allowable option within the Red Bookformat, but has never been implemented.Monauralaudio has

no existing standard on a Red BookCD; mono-source material thus is usually presented as two

identical channels in a standard Red Bookstereo track.

CD-Textis an extension of the Red Bookspecification for audio CD that allows for storage of

additional text information (e.g., album name, song name, artist) on a standards-compliant audio CD.

The information is stored either in thelead-in areaof the CD, where there is roughly five kilobytes of

space available, or in thesubcodechannels R to W on the disc, which can store about 31 megabytes.
http://en.wikipedia.org/wiki/Norio_Ohgahttp://en.wikipedia.org/wiki/Norio_Ohgahttp://en.wikipedia.org/wiki/Norio_Ohgahttp://en.wikipedia.org/wiki/London_Philharmonic_Orchestrahttp://en.wikipedia.org/wiki/London_Philharmonic_Orchestrahttp://en.wikipedia.org/wiki/London_Philharmonic_Orchestrahttp://en.wikipedia.org/wiki/Beethoven%27s_Ninth_Symphonyhttp://en.wikipedia.org/wiki/Beethoven%27s_Ninth_Symphonyhttp://en.wikipedia.org/wiki/Beethoven%27s_Ninth_Symphonyhttp://en.wikipedia.org/wiki/Compact_disc#cite_note-Ohgaobituary-8http://en.wikipedia.org/wiki/Compact_disc#cite_note-Ohgaobituary-8http://en.wikipedia.org/wiki/Compact_disc#cite_note-Ohgaobituary-8http://en.wikipedia.org/wiki/Super_Audio_CDhttp://en.wikipedia.org/wiki/Super_Audio_CDhttp://en.wikipedia.org/wiki/Super_Audio_CDhttp://en.wikipedia.org/wiki/DVDhttp://en.wikipedia.org/wiki/DVDhttp://en.wikipedia.org/wiki/DVDhttp://en.wikipedia.org/wiki/HD_DVDhttp://en.wikipedia.org/wiki/HD_DVDhttp://en.wikipedia.org/wiki/HD_DVDhttp://en.wikipedia.org/wiki/Blu-ray_Dischttp://en.wikipedia.org/wiki/Blu-ray_Dischttp://en.wikipedia.org/wiki/Blu-ray_Dischttp://en.wikipedia.org/wiki/Mini_CDhttp://en.wikipedia.org/wiki/Mini_CDhttp://en.wikipedia.org/wiki/Mini_CDhttp://en.wikipedia.org/wiki/Mini_CDhttp://en.wikipedia.org/wiki/Single_(music)http://en.wikipedia.org/wiki/Single_(music)http://en.wikipedia.org/wiki/Single_(music)http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Maxi_singlehttp://en.wikipedia.org/wiki/Maxi_singlehttp://en.wikipedia.org/wiki/Maxi_singlehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Megabytehttp://en.wikipedia.org/wiki/Megabytehttp://en.wikipedia.org/wiki/Megabytehttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=10http://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Pulse-code_modulationhttp://en.wikipedia.org/wiki/Pulse-code_modulationhttp://en.wikipedia.org/wiki/Pulse-code_modulationhttp://en.wikipedia.org/wiki/44.1_kHzhttp://en.wikipedia.org/wiki/44.1_kHzhttp://en.wikipedia.org/wiki/44.1_kHzhttp://en.wikipedia.org/wiki/Four-channel_Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Four-channel_Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Four-channel_Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Monauralhttp://en.wikipedia.org/wiki/Monauralhttp://en.wikipedia.org/wiki/Monauralhttp://en.wikipedia.org/wiki/CD-Texthttp://en.wikipedia.org/wiki/CD-Texthttp://en.wikipedia.org/wiki/Optical_disc_authoring#Lead-Inhttp://en.wikipedia.org/wiki/Optical_disc_authoring#Lead-Inhttp://en.wikipedia.org/wiki/Optical_disc_authoring#Lead-Inhttp://en.wikipedia.org/wiki/Compact_Disc_subcodehttp://en.wikipedia.org/wiki/Compact_Disc_subcodehttp://en.wikipedia.org/wiki/Compact_Disc_subcodehttp://en.wikipedia.org/wiki/File:Comparison_disk_storage.svghttp://en.wikipedia.org/wiki/Compact_Disc_subcodehttp://en.wikipedia.org/wiki/Optical_disc_authoring#Lead-Inhttp://en.wikipedia.org/wiki/CD-Texthttp://en.wikipedia.org/wiki/Monauralhttp://en.wikipedia.org/wiki/Four-channel_Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/44.1_kHzhttp://en.wikipedia.org/wiki/44.1_kHzhttp://en.wikipedia.org/wiki/Pulse-code_modulationhttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=9http://en.wikipedia.org/wiki/Megabytehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Maxi_singlehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Single_(music)http://en.wikipedia.org/wiki/Mini_CDhttp://en.wikipedia.org/wiki/Mini_CDhttp://en.wikipedia.org/wiki/Blu-ray_Dischttp://en.wikipedia.org/wiki/HD_DVDhttp://en.wikipedia.org/wiki/DVDhttp://en.wikipedia.org/wiki/Super_Audio_CDhttp://en.wikipedia.org/wiki/Compact_disc#cite_note-Ohgaobituary-8http://en.wikipedia.org/wiki/Beethoven%27s_Ninth_Symphonyhttp://en.wikipedia.org/wiki/London_Philharmonic_Orchestrahttp://en.wikipedia.org/wiki/Norio_Ohga


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Compact Disc + Graphicsis a special audio compact disc that contains graphics data in addition to

the audio data on the disc. The disc can be played on a regular audio CD player, but when played on

a special CD+G player, can output a graphics signal (typically, the CD+G player is hooked up to a

television set or a computer monitor); these graphics are almost exclusively used to display lyrics on a

television set forkaraokeperformers to sing along with. The CD+G format takes advantage of the

channels R through W. These six bits store the graphics information.

CD + Extended Graphics(CD+EG, also known as CD+XG) is an improved variant of theCompact

Disc + Graphics(CD+G) format. Like CD+G, CD+EG utilizes basic CD-ROM features to display text

and video information in addition to the music being played. This extra data is stored

insubcodechannels R-W. Very few, if any, CD+EG discs have been published.

Super Audio CD [edit]

Main article:Super Audio CD

Super Audio CD (SACD) is a high-resolution read-onlyopticalaudio discformat that was designed to

providehigher fidelitydigital audio reproduction than the Red Book. Introduced in 1999, it wasdeveloped by Sony and Philips, the same companies that created the Red Book. SACD was in

aformat warwithDVD-Audio,but neither has replaced audio CDs. The SACD standard is referred to

the Scarlet Bookstandard.

Titles in the SACD format can be issued as hybrid discs; these discs contain the SACD audio stream

as well as a standard audio CD layer which is playable in standard CD players, thus making

thembackward compatible.

CD-MIDI [edit]

CD-MIDIis a format used to store music-performance data which upon playback is performed by

electronic instruments that synthesize the audio. Hence, unlike Red Book, these recordings are notaudio.

CD-ROM [edit]

Main article:CD-ROM

For the first few years of its existence, the CD was a medium used purely for audio. However, in 1985

the Yellow BookCD-ROMstandard was established by Sony and Philips, which defined a non-volatile

optical datacomputer data storagemedium using the same physical format as audio compact discs,

readable by a computer with a CD-ROM drive.

Video CD (VCD) [edit]

Main article:Video CD

Video CD (VCD, View CD, and Compact Disc digital video) is a standarddigitalformat for storing

video media on a CD. VCDs are playable in dedicated VCD players, most modernDVD-Videoplayers,

personal computers, and some video game consoles.

The VCD standard was created in 1993 by Sony, Philips,Matsushita,andJVCand is referred to as

the White Bookstandard.

Overall picture quality is intended to be comparable toVHSvideo. Poorly compressed VCD video can

sometimes be lower quality than VHS video, but VCD exhibits block artifacts rather than analog noise,

and does not deteriorate further with each use, which may be preferable.
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352x240 (orSIF)resolution was chosen because it is half the vertical, and half the horizontal

resolution of NTSC video. 352x288 is similarly one quarter PAL/SECAM resolution. This

approximates the (overall) resolution of an analog VHS tape, which, although it has double the

number of (vertical) scan lines, has a much lower horizontal resolution.

Super Video CD [edit]Main article:Super Video CD

Super Video CD (Super Video Compact Disc or SVCD) is a format used for storing video media on

standard compact discs. SVCD was intended as a successor to VCD and an alternative to DVD-

Video, and falls somewhere between both in terms of technical capability and picture quality.

SVCD has two-thirds theresolutionof DVD, and over 2.7 times the resolution of VCD. One CD-R disc

can hold up to 60 minutes of standard quality SVCD-format video. While no specific limit on SVCD

video length is mandated by the specification, one must lower the video bit rate, and therefore quality,

to accommodate very long videos. It is usually difficult to fit much more than 100 minutes of video

onto one SVCD without incurring significant quality loss, and many hardware players are unable toplay video with an instantaneous bit rate lower than 300 to 600kilobitsper second.

Photo CD [edit]

Main article:Photo CD

Photo CD is a system designed byKodakfor digitizing and storing photos on a CD. Launched in

1992, the discs were designed to hold nearly 100 high quality images, scanned prints and slides using

special proprietary encoding. Photo CDs are defined in the Beige Bookand conform to theCD-ROM

XAand CD-i Bridge specifications as well. They are intended to play on CD-i players, Photo CD

players and any computer with the suitable software irrespective of theoperating system.The images

can also be printed out on photographic paper with a special Kodak machine. This format is not to beconfused with KodakPicture CD,which is a consumer product in CD-ROM format.

CD-i [edit]

Main article:Philips CD-i

The PhilipsGreen Bookspecifies a standard for interactive multimedia compact discs designed

forCD-iplayers (1993). This format is unusual because it hides the initial tracks which contains the

software and data files used by CD-i players by omitting the tracks from the disc's TOC (table of

contents). This causesaudio CDplayers to skip the CD-i data tracks. This is different from theCD-i

Readyformat, which puts CD-i software and data into thepregapof track 1.

Enhanced CD [edit]

Main article:Enhanced CD

Enhanced CD, also known as CD Extra and CD Plus, is acertification markof theRecording Industry

Association of Americafor various technologies that combine audio and computer data for use in both

compact disc andCD-ROMplayers.

The primary data formats for Enhanced CDs aremixed mode(Yellow BookCD-ROM/Red BookCD-

DA),CD-i,hidden track, and multisession (Blue Book).

VinylDisc [edit]

Main article:VinylDisc
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wiki/CD-ROMhttp://en.wikipedia.org/wiki/Mixed_Mode_CDhttp://en.wikipedia.org/wiki/CD-ROMhttp://en.wikipedia.org/wiki/Recording_Industry_Association_of_Americahttp://en.wikipedia.org/wiki/Recording_Industry_Association_of_Americahttp://en.wikipedia.org/wiki/Certification_markhttp://en.wikipedia.org/wiki/Enhanced_CDhttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=18http://en.wikipedia.org/wiki/Pregap#Computer_data_in_pregaphttp://en.wikipedia.org/wiki/CD-i_Readyhttp://en.wikipedia.org/wiki/CD-i_Readyhttp://en.wikipedia.org/wiki/Compact_Disc_Digital_Audiohttp://en.wikipedia.org/wiki/Philips_CD-ihttp://en.wikipedia.org/wiki/Green_Book_(CD_standard)http://en.wikipedia.org/wiki/Philips_CD-ihttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=17http://en.wikipedia.org/wiki/Picture_CDhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/CD-ROM_XAhttp://en.wikipedia.org/wiki/CD-ROM_XAhttp://en.wikipedia.org/wiki/Kodakhttp://en.wikipedia.org/wiki/Photo_CDhttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=16http://en.wikipedia.org/wiki/Kilobitshttp://en.wikipedia.org/wiki/Display_resolutionhttp://en.wikipedia.org/wiki/Super_Video_CDhttp://en.wikipedia.org/w/index.php?title=Compact_disc&action=edit&section=15http://en.wikipedia.org/wiki/Source_Input_Format


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VinylDisc is the hybrid of a standard Audio CD and thevinyl record.The vinyl layer on the disc's label

side can hold approximately three minutes of music.

Manufacture [edit]

Main article:CD manufacturing

Individual pits are visible on the micrometre scale

Replicated CDs are mass-produced initially using a hydraulic press. Small granules of heated raw

polycarbonate plastic are fed into the press. A screw forces the liquefied plastic into the mold cavity.

The mold closes with a metal stamper in contact with the disc surface. The plastic is allowed to cool

and harden. Once opened, the disc substrate is removed from the mold by a robotic arm, and a

15 mm diameter center hole (called a stacking ring) is created. The time it takes to "stamp" one CD, isusually 2 to 3 seconds.

This method produces the clear plastic blank part of the disc. After a metallic reflecting layer (usually

aluminum, but sometimes gold or other metal) is applied to the clear blank substrate, the disc goes

under a UV light for curing and it is ready to go to press. To prepare to press a CD, a glass master is

made, using a high-powered laser on a device similar to a CD writer. The glass master is a positive

image of the desired CD surface (with the desired microscopic pits and lands). After testing, it is used

to make a die by pressing it against a metal disc.

The die is a negative image of the glass master: typically, several are made, depending on the

number of pressing mills that are to make the CD. The die then goes into a press and the physical

image is transferred to the blank CD, leaving a final positive image on the disc. A small amount of
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lacquer is applied as a ring around the center of the disc, and rapid spinning spreads it evenly over

the surface. Edge protection lacquer is applied before the disc is finished. The disc can then be

printed and packed.

Manufactured CDs that are sold in stores are sealed via a process called "polywrapping" or shrink

wrapping.The most expensive part of a CD is thejewel case.In 1995, material costs were 30 cents for the jewel

case and 10 to 15 cents for the CD. Wholesale cost of CDs was $0.75 to $1.15, which retailed for

$16.98[citation needed]

. On average the store received 35 percent of the retail price, the record company

27 percent, the artist 16 percent, the manufacturer 13 percent, and the distributor 9 percent.[26]

When

8-track tapes, cassette tapes, and CDs were introduced, each was marketed at a higher price than

the format they succeeded, even though the cost to produce the media was reduced. This was done

because the apparent value increased. This continued from vinyl to CDs but was broken when Apple

marketed MP3s for $0.99, and albums for $9.99. The incremental cost, though, to produce an MP3 is

essentially zero.[27]

Writable compact discs [edit]

Recordable CD [edit]

700MBCD-R next to amechanical pencil

Main article:CD-R

Recordable Compact Discs,CD-Rs,are injection molded with a "blank" data spiral. A photosensitivedye is then applied, after which the discs are metalized and lacquer-coated. The write laser of theCD

recorderchanges the color of the dye to allow the read laser of a standardCD playerto see the data,

just as it would with a standard stamped disc. The resulting discs can be read by most CD-ROM

drives and played in most audio CD players. CD-Rs follow the Orange Bookstandard.

CD-R recordings are designed to be permanent. Over time the dye's physical characteristics may

change, however, causing read errors and data loss until the reading device cannot recover with error

correction methods. The design life is from 20 to 100 years, depending on the quality of the discs, the

quality of the writing drive, and storage conditions. However, testing has demonstrated such

degradation of some discs in as little as 18 months under normal storage conditions.[28][29]

This failure

is known asdisc rot.
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The recordable audio CD is designed to be used in a consumer audio CD recorder. These consumer

audio CD recorders use SCMS (Serial Copy Management System), an early form ofdigital rights

management(DRM), to conform to the AHRA (Audio Home Recording Act). The Recordable Audio

CD is typically somewhat more expensive than CD-R due to lower production volume and a

3%AHRA royaltyused to compensate the music industry for the making of a copy.[30]

High-capacity recordable CDis a higher density recording format that can hold 90 or 99 minutes of

audio on a 12 cm (5 in) disc (compared to about 80 minutes for Red Bookaudio), or 30 minutes of

audio on an 8 cm (3 in) disc (compared to about 24 minutes for Red Bookaudio).[31]

ReWritable CD [edit]

Main article:CD-RW

CD-RWis 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 properties (amorphous vs. crystalline) of the alloy, and hence

change its reflectivity. A CD-RW does not have as great a difference in reflectivity as a pressed CD or

a CD-R, and so many earlier CD audio players cannotread CD-RW discs, althoughmostlater CDaudio players and stand-aloneDVDplayers can. CD-RWs follow the Orange Bookstandard.

The ReWritable Audio CD is designed to be used in a consumer audio CD recorder, which won't

(without modification) accept standard CD-RW discs. These consumer audio CD recorders use

theSerial Copy Management System(SCMS), an early form ofdigital rights management(DRM), to

conform to the United States'Audio Home Recording Act(AHRA). The ReWritable Audio CD is

typically somewhat more expensive than CD-RW due to (a) lower volume and (b) a 3%AHRA

royaltyused to compensate the music industry for the making of a copy.[30]

Speed [edit]

Due to technical limitations, the original ReWritable CD could be written no faster than 4x speed. HighSpeed ReWritable CD has a different design that permits writing at speeds ranging from 4x to 12x.

Original CD-RW drives can only write to original ReWritable CDs. High Speed CD-RW drives can

typically write to both original ReWritable CDs and High Speed ReWritable CDs. Both types of CD-

RW discs can be read in most CD drives. Higher speed CD-RW discs, Ultra Speed (16x to 24x write

speed) and Ultra Speed+ (32x write speed), are now available.

Copy protection [edit]

Main article:CD/DVD copy protection

The Red Bookaudio specification, except for a simple 'anti-copy' statement in the subcode, does not

include anycopy protectionmechanism. Starting in early 2002, attempts were made by record

companies to market "copy-protected" non-standard compact discs, which cannot be ripped, or

copied, to hard drives or easily converted to MP3s. One major drawback to these copy-protected

discs is that most will not play on either computer CD-ROM drives, or some standalone CD players

that use CD-ROM mechanisms. Philips has stated that such discs are not permitted to bear the

trademarked Compact Disc Digital Audiologo because they violate the Red Bookspecifications.

Numerous copy-protection systems have been countered by readily available, often free, software.
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