Writable and Rewritable CDs

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Writable and Rewritable CDs

• By
• Thomas Szychowski

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The CD

• Written from inside out
• TOC is written first
• Last two mm left open
• Three types
• Pressed
• CD-R
• CD-RW

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Pressed CD

• Data is pressed on an aluminum layer
• Physical Pits and Lands
• Data is seen through the transition from one
  depth to another

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Differences from Pressed and burned CDs

• Pressed
• Metallic layer with different heights
• Burned
• Everything is generally at the same height
• Reflection is manipulated using lasers to create
  differences
• Compounds are dyes that are responsive to
  localized heat

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CD-R

• CD Recordable
• Data kept on an organic dye compound
• Normally reflective
• Laser burns areas in the die to represent a
  bump
• Heats the dye to a critical point to change the
  materials properties
• Burned areas are far less reflective than
  non-burned ones
• Permanent and irreversible

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CD-RW

• CD Rewritable
• Phase changing data layer
• Data is kept on a special combination of
  antimony, indium, silver and tellurium
• Reflective originally
• Three laser powers
• Read power
• Lowest power setting
• Erase power
• More powerful than Read-power
• Sets the compound from Dull back to original
  state when cooled
• Write power
• most powerful
• Creates a non-reflected area
• Heated area is non-crystalline when cooled

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Laser Power CD-R

• cyanine dye
• 6.5 mW at burn-speed of 1x
• Faster burn speed means more powerful laser.
• Phthalocyanine
• Alternative to cyanine dye
• Excellent longevity
• Lower powered laser at 1x 5.5mW

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Laser Power CD-RW

• Power levels
• Read State
• Low power
• Low enough to not affect the chemical compound
• Erase State
• Medium power
• Temperature is below the melting point, but above
  the crystalline temp (200ºC)
• Atoms revert to crystalline form
• Write State
• Highest power
• Temperature rises to 500ºC to 700ºC
• creates an amorphous state

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Questions
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