Post on 30-Dec-2015
COEN 180
Optical Storage
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.
Optical Removable Storage
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 ... Spiral track (spiraling outwards) CD pit 0.5 * 2 m
Dust 40 m Human Hair 70 m
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
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
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.
CD-ROM ... Focus laser beam on land area
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 ...
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 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
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
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 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.
CD-RW
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.
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.
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.
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.
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.