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Please note that this chapter is in outline form and will be fleshed out later. Use it to guide you through your own research.
Original optical media
Information recorded as pits of varying lengths
Laser focused on pits. Light reflected back to optical sensor.
CAV
Constant Angular Velocity
Disk spins at constant speed
Each track carries two TV fields (one frame)
Information can be seen by eye
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| A CAV Laserdisc. You can see the separation between fields as a wedge that looks different from the rest of the disc. |
CLV
Constant Linear Velocity
More fields around outer track than inner track
Disc spins slower when reading outer tracks to compensate for extra information
Transitions between fields cannot be seen by eye because they don't line up as they do on CAV discs.
Analog system
Length of pit represents a voltage
Disc sizes
Most discs were 12 inches. 7-inch, 7.9-inch and 4.7-inch were also available.
Gas laser vs LED laser
Early players had a gas (Helium-Neon) laser.
Limited lifespan of HeNe laser limited the life of the player
Later players used LED laser.
Players lasted longer
Typically also played CDs. Later versions played DVDs.
Spiral track of pits
Long pit = 1
Short pit = 0
Laser focused on pits
Data is on label side covered by lacquer
Multi-layer DVD/Blu-Ray
laser focuses on different layers.
Unfocused layers invisible to system
CD
Made possible by cheap infrared LED lasers
DVD uses same technology as CD with smaller pits
Made possible by cheap red LED lasers
Blu-Ray uses same technology as CD and DVD, with smaller pits
Made
possible by cheap blue LED lasers
CD-R, DVD-R, BD-R
Ink darkened by high-power laser
Older players cannot
read recordable
CDs
CD-RW, DVD-RW, DVD+RW, BD-RW
RW stands for "Rewritable", not "Read/Write"
phase-change metal alloy that changes reflectivity at different temperatures
One laser power level writes, another power level erases.
Older players that could read CD-R could not read CD-RW
CD player that can read any CD format are called "Multiread"
DVD+RW is better-suited for on-disk editing than DVD-RW. Otherwise, they are about the same
Obsolete
Smaller magnetic domains can be created because domains don't tend to enlarge over time as in regular floppy disks. The disk must be warmed by a laser for writing. Writing is by a magnetic head, as in floppy disks. Disks are read optically by laser and optical sensor.
Bournelli
LS-120
Zip disk
Jazz disk
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