Author: Terry Ripple
Date: 10:36:52 09/06/02
Go up one level in this thread
On September 06, 2002 at 12:11:21, Roy Eassa wrote:
>On September 06, 2002 at 12:05:06, Roy Eassa wrote:
>
>>On September 06, 2002 at 10:58:55, William H Rogers wrote:
>>
>>>On September 06, 2002 at 10:17:06, Roy Eassa wrote:
>>>
>>>>On September 05, 2002 at 17:49:35, William H Rogers wrote:
>>>>
>>>>>Sarah that sounds like my sons excuse to his teachers "my dog ate my homework"
>>>>>VCR tapes and floppy disks are suppost to have a useful life of about 10 years,
>>>>>while CD's and DVD's should last about 100 years. Scratched CD's can easily be
>>>>>repaired. The surface of the CD is only a plastic coating to protect the metal
>>>>>disk that contains the information.
>>>>>Just joking about the 'dog'
>>>>>Bill
>>>>
>>>>
>>>>Aren't the pits (the data) actually in plastic, with the metal there for
>>>>reflective purposes only?
>>>No. My engineers have told me that the metal is where the data is recoreded, and
>>>that is why you can polish the surface of a damaged cd and restore its contents.
>>>I am talking about scratches, etc. By encasing the metal in plastic, the metal
>>>is kept from oxidizing and thus extending its life for years and years.
>>>Bill
>>
>>
>>Still, respectfully, I've definitely read detailed articles that show that the
>>pits are burned into the part of the plastic that's right next to the metal (and
>>far from the scratchable surface). Further, I've read that it's a common
>>misconception that the data is in the metal. I'll do a search on the 'net to
>>see if I can back this up.
>>
>>
>>Here's one to start:
>>
>>http://www.ee.washington.edu/conselec/CE/kuhn/cdaudio/95x6.htm
>>
>>"Pits are formed in the polycarbonate disk by an injection molding process."
>
>
>
>A couple more:
>
>
>http://www.ee.washington.edu/conselec/W94/edward/edward.htm
>
>"A 50 mW argon ion laser lathe operating at 488 nm then vaporizes sections of
>the plastic, actually burning the pits into the plastic itself."
>
>
>This site says that the *master* disc has its data burned into metal, but the
>ones you and I buy have the data burned into the plastic:
>
>http://www.new-sng.com/cddisc1.cfm
>
>"That machine uses injection molding technology and a high-strength liquid
>plastic called polycarbonate. This polycarbonate plastic makes CDs virtually
>indestructible - it's like the material used for bulletproof windows. Before
>moving to be packaged, the newly-formed disc is cooled with water and removed
>from the mold. The pitted side of the CD is then coated with aluminum and
>protected against scratches with a clear sealer."
>
>
>And finally:
>
>http://www.sanyolaserproducts.com/cd/
>
>"The molded plastic compact disc incorporates a continuous spiral of pits, which
>contain the data. An aluminum reflective layer allows a laser in the compact
>disc drive to read the encoded information. Data integrity is protected by a
>lacquer coating on one side and a plastic substrate on the other side."
----------------------
What about the Cd's we buy to burn? I believe our home CD burners burn the copy
on the thin foil glued on top of the CD. I removed this foil on one of my broken
Cd's and it is extremely thin. I assume that this very thin metalic foil is made
this way so our home CD burners can burn into it because the lasers are not as
powerful as the big commercial ones. And like you say, the original Cd's are
burned into the plastic!
Regards,
Terry
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