GERD GUENTHER / SCIENCE PHOTO LIBRARY GERD GUENTHER / SCIENCE PHOTO LIBRARY
CD vs DVD surface. Light micrograph comparing the surface of a compact disc (CD, lower right) with that of a DVD (upper left). Both discs are pressed with a series of fine depressions, or pits, (dots) representing a digitised musical signal capable of being read by a laser. Each depression is either long or short, and represents a bit. Eight bits form a byte. CDs can hold millions of bytes of data, whereas the increased number of pits on the DVD show that it is capable of holding many times the data of a CD. Magnification: x900 when printed 10 centimetres wide.
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