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COEN 180 Optical Storage. Store data based on the optical properties of a device. Strong,...
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Transcript of COEN 180 Optical Storage. Store data based on the optical properties of a device. Strong,...
![Page 1: COEN 180 Optical Storage. Store data based on the optical properties of a device. Strong, established market for removable media. Small market for archival.](https://reader031.fdocuments.us/reader031/viewer/2022032606/56649e8a5503460f94b9071b/html5/thumbnails/1.jpg)
COEN 180
Optical Storage
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Optical Storage Store data based on the optical properties
of a device. Strong, established market for removable
media. Small market for archival storage.
WORM devices. Magneto-Optical
Harder to erase data accidentally.
Storage density limited by wavelength of light used.
Shift from red to blue laser.
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Optical Removable Storage
Video Disk 1970s 1982 CD-DA (Phillips, Sony) 1985 CD-ROM (Phillips, Sony) 1995 DVD (Phillips, Sony, Toshiba,
Time Warner)
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CD-ROM
CD-ROM: Standard Example for Optical Storage
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CD-ROM ... Spiral track (spiraling outwards) CD pit 0.5 * 2 m
Dust 40 m Human Hair 70 m
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CD-ROM ...
Disk Geometry 12 cm diameter 1.2 mm thick 1.5 cm center hole Spins at
Constant linear velocity (CVL) Constant angular velocity (CAL)
Areal density is 2Mb/mm2
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CD-ROM ...
74 minutes of music 2 channels 44,100 samples/channel/second 2 B / sample 74 minutes 60 sec/minute = 783,216,000 B
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CD-ROM ... X-rating
1X = 150 KB/sec Up to 12X use CLV
Adjust speed so that tracks are read at constant speed.
After 12X use CAV Easier to build faster motors. Data rate now varies. X-rating is then an average.
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CD-ROM ... Focus laser beam on land area
Sharp reflection from land. Dispersion from pit.
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CD-ROM ...
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CD-ROM ...
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CD-ROM ...
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CD-ROM ...
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CD-ROM ...
Mistracking detection:
Main beam reads data, side beams tell whether there is a misregistration.
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CD-ROM ...
Data encoding In principle, pits could be ones,
lands zero, or vice versa. But long sequences are hard to
detect. Use EFM modulation
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CD-ROM EFM 8-14 modulation code words of length 14 bits that consists
of single ones separated by two to nine zeroes
0000 1010 1001 0001 0000 00. The pits range in length from 3 bits to 11
bits. http://www.physics.udel.edu/~watson/
scen103/efm.html
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CD-ROM ...Designation Size Byte NumbersSynchronization 12B 0-11Header 4B 12-15User Data 2048B 16-2063Error Detection 4B 2064-2067Space 8B 2068-2075Error Correction 276B 2076-2351
Table 2: ECMA-130 Media Standard for Block
Layout
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CD Formats
CD-Audio ICE 908 Red Book
CD-ROM ISO/IEC 10149 Yellow Book
CD-I Green Book
Video CD White Book
CD-recordable ISO/IEC 11172/1/2/3 Orange Book
Logical Format
CD-ROM ISO-9660 High Sierra
CD-Recordable ECMA 168 / IS 13940 Frankfurt Proposal
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CD-R
CD-R disks have a layer of dye over the reflecting aluminium layer. The dye is photo-sensitive. In normal state, the dye is translucent, but after heating at a given frequency of light, the dye turns opaque, allowing us to store the data. A CD-R optical heat needs two laser light sources, to generate the write and the less intense read light. A CD-R disk has grooves pressed in to enable tracking with the read laser.
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CD-RW
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CD-RW Can erase, i.e. undo the effect of a write. Use phase shift compounds
Two phases of different reflectivity. Compound of
Silver Antimony Tellurium Indium.
Melts at 600o C If it cools rapidly, it remains in a fluid, amorphous state
that is quite opaque. If the cooling is slower, then the compound crystallizes
into a quite translucent form at around 200oC.
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CD-RW The read layer in a CD-RW burner has
not enough power to melt the compound.
The higher power erase layer can heat the compound to the crystallization point and restore the original crystallization of the compound.
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DVD Same basic technique as CD DVDs can use double layering
Two reflective layers on a single surface. The inner one is made of aluminum (as for CD-
ROM) The outer one is a semi-reflective gold layer
through which the laser can focus on the inner layer.
Maximum data capacity of 17GB, DVDs can be in a double sided, double layered
format, where a total of four surfaces stores data.
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DVD DVDs achieve higher data density per
layer by halfing the dimensions of the pits / bumps on a CD: track pitch 740nm vs 1600 nm minimum pit length is 400 nm (440 nm on a
double layer DVD) vs 830 nm. Since data is stored on a surface, this
effectively quadruples the data density. Use of higher frequency light with a wave
length of 640 nm as opposed to 780 nm for the laser used in CD-ROM.
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DVD
The error correction scheme on a DVD is much more sophisticated and powerfull than the one used for the CD-ROM standards,
Progress in the theory of ECC Progress in the processing of data.