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In computing and optical disc recording technologies, an optical disc ( OD ) is a flat, usually circular disc that encodes binary data (bits) in the form of pits and lands (where change from pit to land or from land to pit corresponds to binary value of 1 , no change, regardless whether in land or pit area, corresponds to binary value of 0 ) on a special material (often aluminum ) on one of its flat surfaces.

The encoding material sits atop a thicker substrate (usually polycarbonate) that makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The data are stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive that spins the disc at speeds of about 200 to 4,000 RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc (outer tracks are read at a higher data speed due to higher linear velocities at the same angular velocities). Most optical discs exhibit a characteristic iridescence as a result of the diffraction grating formed by its grooves. This side of the disc contains the actual data and is typically coated with a transparent material, usually lacquer. The reverse side of a

This article possibly contains original research . Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. ( July 2009 ) (Learn how and when to remove this template message) The first recorded historical use of an optical disc was in 1884 when Alexander Graham Bell, Chichester Bell and Charles Sumner Tainter recorded sound on a glass disc using a beam of light. Optophonie is a very early (1931) example of a recording device using light for both recording and playing back sound signals on a transparent photograph. An early optical disc system existed in 1935, named Lichttonorgel. citation needed 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 ( U.S. Patent 3,430,966 ). It is of special interest that U.S. Patent 4,893,297 , filed 1989, issued 1990, gene

There are numerous formats of optical direct to disk recording devices on the market, all of which are based on using a laser to change the reflectivity of the digital recording medium in order to duplicate the effects of the pits and lands created when a commercial optical disc is pressed. Formats such as CD-R and DVD-R are "Write once read many" or write-once, while CD-RW and DVD-RW are rewritable, more like a magnetic recording hard disk drive (HDD). Media technologies vary, M-DISC uses a different recording technique & media versus DVD-R and BD-R.

This section needs expansion . You can help by adding to it. ( July 2020 ) Optical media can predictively be scanned for errors and media deterioation well before any data becomes unreadable. A higher rate of errors may indicates deteriorating and/or low quality media, physical damage, an unclean surface and/or media written using a defective optical drive. Those errors can be compensated by error correction to some extent. Error scanning software includes Nero DiscSpeed , k-probe , Opti Drive Control (formerly "CD speed 2000" ) and DVD info Pro for Windows, and QPxTool for cross-platform. Support of error scanning functionality varies per optical drive manufacturer and model. Error types edit There are different types of error measurements, including so-called "C1" , "C2" and "CU" errors on CDs, and "PI/PO (pairity inner/outer) errors" and the more critical "PI/PO failures" on DVDs. Finer-grain error measurements on CD

Optical discs are made using replication. This process can be used with all disc types. Recordable discs have pre-recorded vital information, like manufacturer, disc type, maximum speeds, etc. In replication, a cleanroom with yellow light is necessary to protect light sensitive materials and to prevent dust from corrupting the data on the disc. A glass master is used in replication. The master is placed in a machine that cleans it as much as possible using a rotating brush and deionized water, preparing it for the next step. In the next step, a surface analyzer inspects the cleanliness of the master before photoresist is applied on the master. The photoresist is baked in an oven to solidify it. Then, in the exposure process, the master is placed in a turntable where a laser selectively exposes the resist to light. At the same time, a developer and deionized water are applied to the disc to remove the exposed resist. This process forms the pits and lands that represent the data on the

Base (1×) and (current) maximum speeds by generation Generation Base Max (Mbit/s) (Mbit/s) × 1st (CD) 1.17 65.6 56× 2nd (DVD) 10.57 253.6 24× 3rd (BD) 36 504 14× 4th (AD) ? ? 14× Capacity and nomenclature Designation Sides Layers (total) Diameter Capacity (cm) (GB) BD SS SL 1 1 8 7.8 BD SS DL 1 2 8 15.6 BD SS SL 1 1 12 25 BD SS DL 1 2 12 50 BD SS TL 1 3 12 100 BD SS QL 1 4 12 128 CD–ROM 74 min SS SL 1 1 12 0.682 CD–ROM 80 min SS SL 1 1 12 0.737 CD–ROM SS SL 1 1 8 0.194 DDCD–ROM SS SL 1 1 12 1.364 DDCD–ROM SS SL 1 1 8 0.387 DVD–1 SS SL 1 1 8 1.46 DVD–2 SS DL 1 2 8 2.66 DVD–3 DS SL 2 2 8 2.92 DVD–4 DS DL 2 4 8 5.32 DVD–5 SS SL 1 1 12 4.70 DVD–9 SS DL 1 2 12 8.54 DVD–10 DS SL 2 2 12 9.40 DVD–14 DS DL/SL 2 3 12 13.24 DVD–18 DS DL 2 4 12 17.08 DVD–R 1.0 SS SL 1 1 12 3.95 DVD–R (2.0), +R, –RW, +RW SS SL 1