The so-called program area that contains the data commonly starts 25 millimetres away from the center point. Optical discs are usually between 7.6 and 30 cm (3.0 and 11.8 in) in diameter, with 12 cm (4.7 in) being the most common size. Blu-rays have a coating called durabis that mitigates these problems. Unlike the 3 1⁄ 2-inch floppy disk, most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems. The reverse side of an optical disc usually has a printed label, sometimes made of paper but often printed or stamped onto the disc itself. This side of the disc contains the actual data and is typically coated with a transparent material, usually lacquer. Most optical discs exhibit a characteristic iridescence as a result of the diffraction grating formed by their grooves. 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). The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The encoding material sits atop a thicker substrate (usually polycarbonate) that makes up the bulk of the disc and forms a dust defocusing layer. Their main uses are the distribution of media and data, and long-term archival. DVD), or store both on the same disc (e.g. Optical discs can store analog information (e.g. Optical discs can be reflective, where the light source and detector are on the same side of the disc, or transmissive, where light shines through the disc to the be detected on the other side. High-Definition Versatile Multilayer Disc (HD VMD)Īn optical disc is a flat, usually disc-shaped object that stores information in the form of physical variations on its surface that can be read with the aid of a beam of light.HD DVD: HD DVD-R, HD DVD-RW, HD DVD-RAM.Blu-ray Disc ( BD): BD-R & BD-RE, Blu-ray 3D, Mini Blu-ray Disc.DVD: DVD-R, DVD+R, DVD-R DL, DVD+R DL, DVD-R DS, DVD+R DS, DVD-RW, DVD+RW, DVD-RAM, DVD-D, DVD-A, DVD-Video, HVD, EcoDisc, MiniDVD.Compact disc ( CD): CD-DA, CD-ROM, CD-R, CD-RW, 5.1 Music Disc, Super Audio CD ( SACD), Photo CD, CD Video ( CDV), Video CD ( VCD), Super Video CD ( SVCD), CD+G, CD-Text, CD-ROM XA, CD-i, MIL-CD, Mini CD.
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