Re: CD or DVD
- From: Needy <needhelp@xxxxxx>
- Date: Sat, 16 Jul 2005 15:07:21 -0400
On Sat, 16 Jul 2005 19:07:31 +0100, "Alan Smith" <alan@xxxxxxxxxxxx>
wrote:
>
>"Shenan Stanley" <newshelper@xxxxxxxxx> wrote in message
>news:%23R$Cm6iiFHA.2444@xxxxxxxxxxxxxxxxxxxxxxx
>> Joan and Alan wrote in message
>>> Which device is better to store pictures?
>>
>> Alan Smith wrote:
>>> Either, but a CD will probably have a longer life.
>>
>> Actually - being they are based off the same basic technology - their
>> lifespan should be similar; however untested this lifespan may be.
>> If treated well, you can expect the media and the data stored within (on
>> either media type) to be good and available with the proper reader for
>> several years/decades without problem.
>>
>> While tests do show "stamped" CDs and DVDs to last longer than burned CDs
>> and DVDs - enough time hasn't passed to give a true/accurate lifespan for
>> quality CD/DVD media yet.
>>
>> --
>> Shenan Stanley
>> MS-MVP
>> --
>
>The lifespan of user written DVD's is less than that of CD's.
>
Considering how easily damaged CDs and DVDs are, it would make
sense that a DVD would have a shorter lifespan that a CD. Just in
case you aren't familiar with the "burning" process that occurs when
you make a CD or DVD, it's done like this: You have a highly
reflective alloy disk that has a layer of dye covering it. When you
burn a disk, the laser in the burner burns holes in the dye. By
burning holes in the dye, it allows for the reflective alloy disk to
reflect a laser beam during the reading of the disk. By burning holes
or leaving the area intact and not burning a hole, you can replicate
ones and zeros. For example, leaving the area intact so that the
laser can't be reflected back might be a zero, and the burnt hole that
reflects the laser back to itself might be a one.
If you read the proper handling procedures for these disks, they
tell you to never flex a disk, meaning, don't bend one. Heck, just
trying to get one out of the jewel case requires you to slightly bend
it. They say that bending a disk can cause the dye layer to move,
stretch, or distort, and if that happens, the dye can cover over some
of the holes that were burnt in it. If this happens, the disk becomes
corrupted.
If you consider that the DVD has a lot more holes burnt in it in
order to store the 4.38 GB of information that a DVD holds, then that
means that there are more holes that are smaller and packed together
more closely, as opposed to a CD, which only holds 700 MB. That would
make the DVD more susceptible to damage just by removing it from the
jewel box, not to mention all the other factors that can damage a
disk, like heat and light.
If you're wondering about the lifespan of a commercially made DVD
or CD with a movie or music already recorded on it, it's a lot longer
because they don't have a layer of dye. Instead, the reflective alloy
is stamped so that the actual alloy has pits in it. These pits
represent the unburnt areas of dye in a homemade disk, because when
the laser tries to read the pitted areas, the laser is dispersed and
not reflected back, the same as the unburnt dye areas. Since the
alloy is stamped and there's no dye involved, the commercially made
recordings on CDs and DVDs should theoretically last forever.
Needy
.
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