W8IntLect

W8IntLect - Mass Storage-5 Optical CD / DVD 1 Optical...

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1 Mass Storage-5 Optical CD / DVD
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2 Optical storage reads and writes  using light   instead of magnetism Patterns of tiny pits on disc surface represent bits, which are readable by a laser beam. Optical Storage Technology
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3 Writable CD / DVD’s • Originally a read-only device • CD-R (Recordable) • CD-RW (ReWritable) • Store large amounts of data at a cost lower than most other removable random-access mediums.
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4 CD / DVD Data is physically embedded into the disc surface Combines constant linear velocity (CLV) and constant angular velocity (CAV)
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5 Optical Storage Consists of an injection-molded piece of clear polycarbonate plastic. A thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then an acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic.
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6 Optical Storage A single spiral track of data, circling from the inside of the disc to the outside. The fact that the spiral track starts at the center means that the disc can be smaller than 4.8 inches (12 cm) if desired. -CD ROM: written by a manufacturer and read only memory. -CD-R: written only once by a consumer, making these disks  recordable. -CD-RW: written to and erased from 1 to approximately 25  times, making these disks rewritable. -DVD: much higher storage capacity than a CD and a  different storing process.   
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7 Optical Technology for Data • Identical in appearance to CD-DAs (Digital Audio CDs), CD-ROMs store data instead of (or in addition to) audio. • Drives in PCs that read the data discs are almost identical to an audio CD player. Changes in the circuitry provide additional error detection and correction . (Minor errors that could exist in a music file would be unacceptable in a data file)
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8 Pits and Lands • Reading of optical storage media is a matter of bouncing a low-powered laser beam off the reflective layer in the disc. • The laser shines a focused beam on the underside of the disc, and a photosensitive receptor detects when the light is reflected back. • When the light hits a land (flat spot) on the track, the light is reflected back but when the light hits a pit (raised bump), no light is reflected back. The transitions
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9 Mechanical Operation • Optical drives operate in the following manner: – 1. The laser diode emits a low-energy infrared
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This note was uploaded on 04/14/2011 for the course HWD 101 taught by Professor Brain during the Spring '11 term at Seneca.

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W8IntLect - Mass Storage-5 Optical CD / DVD 1 Optical...

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