Transcript Optical Storage Pres.

COEN 180
Optical Storage
Optical Storage
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Store data based on the optical properties of
a device.
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Strong, established market for removable media.
Small market for archival storage.
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WORM devices.
Magneto-Optical
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Harder to erase data accidentally.
Storage density limited by wavelength of light
used.
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Shift from red to blue laser.
Optical Removable Storage
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Video Disk 1970s
1982 CD-DA (Phillips, Sony)
1985 CD-ROM (Phillips, Sony)
1995 DVD (Phillips, Sony, Toshiba, Time
Warner)
CD-ROM
CD-ROM: Standard Example for Optical Storage
CD-ROM ...
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Spiral track (spiraling outwards)
CD pit 0.5 * 2 m
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Dust 40 m
Human Hair 70 m
CD-ROM ...
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Disk Geometry
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12 cm diameter
1.2 mm thick
1.5 cm center hole
Spins at
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Constant linear velocity (CVL)
Constant angular velocity (CAL)
Areal density is 2Mb/mm2
CD-ROM ...
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74 minutes of music
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2 channels
44,100 samples/channel/second
2 B / sample
74 minutes
60 sec/minute
= 783,216,000 B
CD-ROM ...
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X-rating
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1X = 150 KB/sec
Up to 12X use CLV
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Adjust speed so that tracks are read at
constant speed.
After 12X use CAV
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Easier to build faster motors.
Data rate now varies.
X-rating is then an average.
CD-ROM ...
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Focus laser beam on land area
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Sharp reflection from land.
Dispersion from pit.
CD-ROM ...
CD-ROM ...
CD-ROM ...
CD-ROM ...
CD-ROM ...
Mistracking detection:
Main beam reads data, side beams tell whether
there is a misregistration.
CD-ROM ...
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Data encoding
In principle, pits could be ones, lands
zero, or vice versa.
But long sequences are hard to detect.
Use EFM modulation
CD-ROM
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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/scen1
03/efm.html
CD-ROM ...
Designation
Synchronization
Header
User Data
Error Detection
Space
Error Correction
Size Byte
12B
4B
2048B
4B
8B
276B
Numbers
0-11
12-15
16-2063
2064-2067
2068-2075
2076-2351
Table 2: ECMA-130 Media Standard for Block
Layout
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
CD-R
CD-R disks have a layer of dye over the reflecting aluminium layer. The dye is photosensitive. 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.
CD-RW
CD-RW
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Can erase, i.e. undo the effect of a write.
Use phase shift compounds
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Two phases of different reflectivity.
Compound of
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Silver
Antimony
Tellurium
Indium.
Melts at 600o C
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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.
CD-RW
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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.
DVD
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Same basic technique as CD
DVDs can use double layering
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Two reflective layers on a single surface.
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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,
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DVDs can be in a double sided, double layered format,
where a total of four surfaces stores data.
DVD
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DVDs achieve higher data density per layer
by halfing the dimensions of the pits / bumps
on a CD:
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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.
DVD
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The error correction scheme on a DVD
is much more sophisticated and
powerfull than the one used for the CDROM standards,
Progress in the theory of ECC
Progress in the processing of data.