CST8174_Lecture_13_cdrom_drive

CST8174_Lecture_13_cdrom_drive - Algonquin College CST8174...

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Algonquin College CST8174 – 05F CST8174 Computer Technology Basics Optical Storage
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-2 Optical Storage We’ve discussed magnetic storage Floppy drives Hard drives Now we’ll discuss optical storage CD DVD
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-3 CD Media Compact Disc Uses light instead of magnetism to read and write data The first CD media was developed for the recording industry to replace cassettes and vinyl records First audio CD released in 1982 Within a year standards were developed for the storage of data on a CD disc
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-4 CD Data Organization Similar to hard drives in that data is organized in sections Unlike hard drives, CDs have a single continuous track that begins at the center and spirals outward
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-5 CD-ROM Creation Compact Disc – Read Only Memory The basic creation of a CD-ROM disc A pattern of pits and lands is stamped onto a molded polycarbonate disc The stamping process places the data on the disc A reflective metallic coating is applied so that the disc will reflect light Finally the disc is coated with a scratch-resistant lacquer for protection
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-6 Disc Surface The surface of a CD is marked with microscopic indentations Markings Pits Indentations Lands Flat areas
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-7 Disc Surface The pits are tiny indentations created from the top during stamping The laser reads from the bottom where a pit is viewed as a bump A pit is 0.6 microns in width with 1.6 microns between tracks If you could stretch the data track of a CD out flat it would be approximately 5Km long
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-8 CD-ROM Terminology Pickup Single laser-based read/write head Actually a Laser Emitting Diode (LED) Subcode Data Encodes the absolute and relative position of the laser in the track For audio CDs stores such data as title and song length
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-9 CD-ROM Terminology EFM Eight-Fourteen Modulation A complex decoding process to convert a sequence of pits and lands into meaningful information Uses fourteen bits to record a byte Implements error detection Uses flux transitions to encode data Frame Grouping of data bits Similar to a sector or cluster on magnetic media
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-10 CD Layout The disc surface is broken into many areas PCA PMA Lead-in Data Lead-out
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Algonquin College CST8174 – 05F Thursday, May 7, 2009 12-11 CD Layout PCA Power Calibration Area Used to determine the laser power necessary for burn
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CST8174_Lecture_13_cdrom_drive - Algonquin College CST8174...

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