question: How to CDs work, more specifically, how does sound and picture get transmitted from a little disc?
comment: A CD is essentially a layer of metal pressed between two pieces of plastic. To record onto the CD, a laser burns pits into the metal. If there’s a pit, that represents a 0, and if there isn’t, that represents a 1. This is recorded from the inside to the outside in a tight spiral. To read the CD, another laser is shone along the spiral, and a photo sensor is placed so that the reflected light from the shiny bit will hit it and create a small electric current, representing a 1, and the pits don’t. So this electrical signal is read back to a computer that takes that stream of 0s and 1s and interprets it in some way to pass on to computer memory, and then eventually out to a screen or speaker as a pattern of light or a wave of sound.
passages: Section::::Logical format.:Photo CD.
   For the first few years of its existence, the CD was a medium used purely for audio. However, in 1988, the "Yellow Book" CD-ROM standard was established by Sony and Philips, which defined a non-volatile optical data computer data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive.
  
  Section::::Logical format.:Video CD (VCD).
   CD and DVD discs can be used as part of e-communications. Entire marketing presentations, catalogues, brochures and price lists can be stored on a CD. CDs are small and simple to hand out to target audiences and most modern computers have CD drive readers, however most of the same information can be presented on a website or email.
  
  Section::::Integrated marketing communications.
   Although research into optical data storage has been ongoing for many decades, the first popular system was CD, introduced in 1982, adapted from audio (CD-DA) to data storage (the CD-ROM format) with the 1985 "Yellow Book", and re-adapted as the first mass market optical storage medium with CD-R and CD-RW in 1988. Compact Disc is still the "de facto" standard for audio recordings, although its place for other multimedia recordings and optical data storage has largely been superseded by DVD.
   The Compact Disc (CD), which is based on MCA/Philips Laserdisc technology, was developed by a taskforce of Sony 
  
  and Philips in 1979-1980. Toshi Doi and Kees Schouhamer Immink created the digital technologies that turned the analog Laserdisc into a high-density low-cost digital audio disc. The CD, available on the market since October 1982, remains the standard physical medium for sale of commercial audio recordings
   Philips later teamed up with Sony to develop a new type of disc, the compact disc or CD. Introduced in 1982 in Japan (1983 in the U.S. and Europe), the CD is about in diameter, and is single-sided. The format was initially designed to store digitized sound and proved to be a success in the music industry.
   A CD is made from thick, polycarbonate plastic and weighs 15–20 grams. 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.
   Section::::Inner workings.:Analogue signal recovery from the disc.
  
  To read the data from the disc, a laser beam shines on the surface of the disc. Surface differences between discs being played, and tiny position differences once loaded, are handled by using a movable lens with a very close focal length to focus the light on the disc. A low mass lens coupled to an electromagnetic coil is in charge of keeping focused the beam on the 600 nm wide data track.
   CD-Text is an extension of the "Red Book" specification 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 the lead-in area of the CD, where there is roughly five kilobytes of space available, or in the subcode channels R to W on the disc, which can store about 31 megabytes.
   Section::::Further developments and applications.:Computer control.
  
  In the early 1980s, Philips produced a LaserDisc player model adapted for a computer interface, dubbed "professional". In 1985, Jasmine Multimedia created LaserDisc jukeboxes featuring music videos from Michael Jackson, Duran Duran, and Cyndi Lauper. When connected to a PC this combination could be used to display images or information for educational or archival purposes, for example thousands of scanned medieval manuscripts. This strange device could be considered a very early equivalent of a CD-ROM.
   Section::::1946 to 1969.
   Over time, CDs have progressed from being solely for music, to being a format for all kinds of data storage, such as text, images, photos and videos. Educators can use CDs to store educational materials including taped lectures, presentations, and handouts into one compact disc for the student to access on CD players or computers.
  
  Section::::Braille.
   In June 1985, the computer-readable CD-ROM (read-only memory) and, in 1990, CD-Recordable were introduced, also developed by both Sony and Philips. Recordable CDs were a new alternative to tape for recording music and copying music albums without defects introduced in compression used in other digital recording methods. Other newer video formats such as DVD and Blu-ray use the same physical geometry as CD, and most DVD and Blu-ray players are backward compatible with audio CD.
   Section::::Writable compact discs.
  
  Section::::Writable compact discs.:Recordable CD.
  
  Recordable Compact Discs, CD-Rs, are injection-molded with a "blank" data spiral. A photosensitive dye is then applied, after which the discs are metalized and lacquer-coated. The write laser of the CD recorder changes the colour of the dye to allow the read laser of a standard CD player to 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 Book" standard.
   History of optical storage media
  
  Although research into optical data storage has been ongoing for many decades, the first popular system was the Compact Disc, introduced in 1982, adapted from audio (CD-DA) to data storage (the CD-ROM format) with the 1985 "Yellow Book", and re-adapted as the first mass market optical storage medium with CD-R and CD-RW in 1988. Compact Disc is still the "de facto" standard for audio recordings, although its place for other multimedia recordings and optical data storage has largely been superseded by DVD.
   Section::::Logical format.
  
  Section::::Logical format.:Audio CD.
   In the mid-1990s, a consortium of manufacturers (Sony, Philips, Toshiba, Panasonic) developed the second generation of the optical disc, the DVD.
  
  Magnetic disks found limited applications in storing the data in large amount. So, there was the need of finding some more data storing techniques. As a result, it was found that by using optical means large data storing devices can be made which in turn gave rise to the optical discs.The very first application of this kind was the Compact Disc (CD) which was used in audio systems.
   CD Video
  
  CD Video (also known as CDV, CD-V, or CD+V) is a format of optical media disc that was introduced in 1987 that combines the technologies of standard compact disc and LaserDisc. CD-V discs are the same size as a standard 12-cm audio CD, and contain up to 20 minutes' worth of CD Audio that can be played on any audio CD player. It also contains up to 5 minutes of LaserDisc video information with digital CD-quality sound, which can be played back on a newer LaserDisc player capable of playing CD-V discs. 
  
  Section::::Description.
   Section::::Further developments and applications.:Picture discs.
  
  Picture discs have artistic etching on one side of the disc to make the disc more visually attractive than the standard shiny silver surface. This etching might look like a movie character, logo, or other promotional material. Sometimes that side of the LD would be made with colored plastic, rather than the clear material used for the data side. Picture disc LDs only had video material on one side as the "picture" side could not contain any data. Picture discs are rare in North America.
  
  Section::::Further developments and applications.:LD-G.
   CD-ROM discs are read using CD-ROM drives. A CD-ROM drive may be connected to the computer via an IDE (ATA), SCSI, SATA, FireWire, or USB interface or a proprietary interface, such as the Panasonic CD interface, LMSI/Philips, Sony and Mitsumi standards. Virtually all modern CD-ROM drives can also play audio CDs (as well as Video CDs and other data standards) when used with the right software.
  
  Section::::CD-ROM drives.:Laser and optics.
   The CD-ROM format was developed by Sony and Denon, introduced in 1984, as an extension of Compact Disc Digital Audio and adapted to hold any form of digital data. The same year, Sony demonstrated a LaserDisc data storage format, with a larger data capacity of 3.28 GB.
  
  In the late 1980s and early 1990s, Optex, Inc. of Rockville, MD, built an erasable optical digital video disc system using Electron Trapping Optical Media (ETOM). Although this technology was written up in Video Pro Magazine's December 1994 issue promising "the death of the tape", it was never marketed.
   BULLET::::- The Compact Disc, or CD, is an optical disc used to store digital data, originally developed for storing digital audio. In 1965, James Russell acted upon his idea that the music industry needed a new medium whereby a gramophone record and the needle on a phonograph would no longer come into contact with one another. With an interest in lasers, Russell soon began his research in an optical system that would replace a phonograph's needle and replace it with a laser that would read codes in order to record and playback sound. At 12 inches (30 cm) in diameter, Russell in 1970 had successfully invented and built the world's first compact disc that contained digitized codes etched onto the disc that could be read from a laser. After partnering with Digital Recording which was later acquired by Optical Recording Corporation, Russell and the parent company that he worked for, found it increasingly difficult to enforce and protect his patents from infringement by competitors such as Sony, Philips, and Time Warner who all profited from Russell's invention. The belief that Dutch and Japanese scientists "invented" the compact disc is a misconception in the sense that Philips and Sony used Russell's underlying technology in order to develop a disc more refined, practical, smaller and sophisticated. In 1982, Sony and Philips had "commercially" introduced the compact disc, twelve years after Russell had already created a working prototype in 1970. By 1986, Optical Recording decided to legally act by suing Sony, Phillips, and Time Warner. Two years later, the company came to a licensing settlement with Sony and soon thereafter, agreements with Phillips and others soon followed, including a June 1992 court ruling that required Time Warner to pay Optical Recording $30 million due to patent infringement.
   An early optical disc system existed in 1935, named .
  
  An early analog optical disc used for video recording was invented by David Paul Gregg in 1958 and patented in the US in 1961 and 1969. This form of optical disc was a very early form of the DVD (). It is of special interest that , filed 1989, issued 1990, generated royalty income for Pioneer Corporation's DVA until 2007 —then encompassing the CD, DVD, and Blu-ray systems. In the early 1960s, the Music Corporation of America bought Gregg's patents and his company, Gauss Electrophysics.
   Section::::Classification.
  
  Video discs can be classed based on their playback mechanism:
  
  BULLET::::- Mechanical
  
  BULLET::::- Phonovision
  
  BULLET::::- Phonovid
  
  BULLET::::- Ted
  
  BULLET::::- Visc
  
  BULLET::::- Capacitance Based
  
  BULLET::::- CED, VHD
  
  BULLET::::- Optical discs
  
  BULLET::::- Reflective
  
  BULLET::::- LaserDisc, CD, DVD, Blu-ray, etc.
  
  BULLET::::- Transmissive
  
  BULLET::::- Thomson CSF system
  
  BULLET::::- Laserfilm
  
  Section::::See also.
  
  BULLET::::- Multiple sub-Nyquist sampling encoding (MUSE), an early high-definition video system
  
  Section::::References.
  
  Section::::References.:Bibliography.
  
  BULLET::::- Cowie, Jefferson R. "Capital Moves: RCA's Seventy-Year Quest for Cheap Labor". Ithaca, N.Y.: Cornell University Press, 1999. .
   Section::::History.:Further development and decline.
  
  The CD was planned to be the successor of the vinyl record for playing music, rather than primarily as a data storage medium. From its origins as a musical format, CDs have grown to encompass other applications. In 1983, following the CD's introduction, Immink and Braat presented the first experiments with erasable compact discs during the 73rd AES Convention.
  