Licensed from Columbia University Press
Licensed from Columbia University Press
Molded plastic disc containing digital data that is scanned by a laser beam for the reproduction of recorded sound or other information. Since its commercial introduction in 1982, the audio CD has become the dominant format for high-fidelity recorded music. Digital audio data can be converted to analog form to reproduce the original audio signal (see digital-to-analog conversion). Coinvented by Philips Electronics and Sony Corp. in 1980, the compact disc has expanded beyond audio recordings into other storage-and-distribution uses, notably for computers (CD-ROM) and entertainment systems (videodisc and DVD). An audio CD can store just over an hour of music. A CD-ROM can contain up to 680 megabytes of computer data. A DVD, the same size as traditional CDs, is able to store up to 17 gigabytes of data, such as high-definition digital video files.
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Receipt from a bank acknowledging the deposit of a sum of money. The most common type, the time certificate of deposit, is for a fixed-term interest-bearing deposit in a large denomination. It consequently pays higher interest than a savings account, though the investor who withdraws money before its maturity date is subject to a penalty. Introduced in the early 1960s, CDs have become a popular method of saving.
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Metallic chemical element, chemical symbol Cd, atomic number 48. It normally occurs along with other metals, especially zinc, in ores. A silvery white metal capable of taking a high polish, cadmium does not corrode under alkaline (see alkali) conditions; one of its major uses is in electroplating other metals and alloys to protect them. Because it absorbs neutrons effectively, it is used in control rods in some nuclear reactors. Its compounds, in which it has valence 2, are very toxic. They are used as pigments, as phosphors in television and computer monitor screens, as pesticides, and in photographic applications and analytical chemistry.
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Type of computer storage medium that is read optically (e.g., by a laser). A CD-ROM drive uses a low-power laser beam to read digitized (binary) data that have been encoded onto an optical disc in the form of tiny pits, then feeds the data to a computer for processing. Because it uses digital data, a CD-ROM can store images and sound in addition to text and is thus used in video and audio devices to store music, graphics, and movies (see compact disc). Unlike conventional magnetic-storage technologies (e.g., hard disks), CD-ROM drives cannot write information (that is, accept the input of new data), hence the tag “read-only.” Recordable compact discs (called CD-R) must be written on a CD-R recorder and can be played on any CD-ROM drive.
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