Author: Roy Eassa
Date: 10:54:32 09/06/02
Go up one level in this thread
On September 06, 2002 at 13:36:52, Terry Ripple wrote: >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 Home-burnable CDs (CD-Rs & CD-RWs) use some sort of dye mechanism, as I understand it, rather than "burning" into metal or plastic.
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