14 March 2011
CD’s and DVD’s work in practically the same manner. Both store data as a series of reflective marks on the surface of the disc. The thin plastic or metal foil layer of the disc gets hit by the laser beam of the writing drive. The laser energy thus produced creates tiny bumps in a spiral pattern similar to that of a long-playing album.
CD’s and DVD’s work in practically the same manner. Both store data as a series of reflective marks on the surface of the disc.
When you play the disc, it spins around and while doing so, a different laser beam shines on the bumps. The laser light flickers on or off because of the bumps and these flickers are converted into ones and zeroes which make up the language of the computer. The light is reflected back to a sensor and the data is converted into audio, video and general data.
CD’s
A Compact Disc or CD is an optical disc originally created to store and play sound recordings but has evolved through the years into a storage medium for data. Standard CD’s can store up to 80 minutes of uncompressed audio equivalent to 700mb of data.
The CD surface is made up of a polycarbonate layer on which is molded spiral tracks. CD data are stored as a series of “pits” or minute grooves encoded on these spiral tracks. The areas between “pits” are known as “lands.” These pits and lands do not represent the zeroes and ones of binary data. Rather, a change from pit to land (or vice versa) is read as zero while no change is interpreted as one. By a process of decoding and reversing, the raw data stored on the disc can be revealed.
DVD’s
A DVD has the same dimensions as the CD but offers higher storage capacity.
DVD employs a laser diode light of a 650 nm wavelength which is much shorter than the 780 nm wavelength used in CD’s. This allows for etching of smaller pits on the tracks of the DVD which explains the bigger storage capacity of DVD’s.
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