Re: A2 Trade/Swap???? site discovered - What are your thoughts on such a site?

[pausch@saafNOSPAM.se (Paul Schlyter)]

In article <8jdenj$dt0$1@nserve1.acs.ucalgary.ca>,
Byron Desnoyers Winmill <wbdesnoy@acs2.acs.ucalgary.ca> wrote:
 
> Paul Schlyter (pausch@saafNOSPAM.se) wrote:
>: Obsbedia2 <obsbedia2@aol.com> wrote:
>: > Are even CD Roms the way to go?  An article in Time or Newsweek a year or
>: > two ago stated that CD Roms have a lifespan of only 5 years.
>:  
>: Which is clearly erroneous.  My oldest CD-ROM is now 10 years old, and
>: it can still be read with no problem.  I also have some audio CD's which
>: are 15+ years old, and they too are still playable.
> 
> Rather than dismissing the idea, you could ask a few questions.  :-)
> 
> Was this refering to CD-ROM's, CD-R's or CD-RW's?
 
No idea -- he merely said it was "CD's".  And he made e general statement,
without specifics - such statements are usually wrong.
 
> If the media is differnt, then one could outlive the other by decades.
 
Indeed it could!
 
> CD-R's and CD-RW's would also make sense from the user's context (since
> people tend to be more concerned with saving data than with saving
> pre-packaged programs).
> 
> What are the conditions which make the media last longer, or degrade
> faster?  Are CD's sensitive to broad spectrum light?  Are certain
> temperatures ideal for storing the CD.  Can humidity or biological
> factors influence the life of the media.  Humidity may be an issue
> for somebody living in Vancover, but not an issue for somebody living
> in Red Deer.
 
All this probalby matters.  Thus, a CD which is left out exposed to
direct sunlight on all clear days will probably have a lifespan much
shorter than a CD stored in relative darkness when not in use.
Exacty how much shorter I don't know - if you want to find out,
you'll have to experiment.
 
> How much data is lost after the given time span?  Loosing a couple
> of bits on a partially filled CD would not make much of a difference.
> Loosing a couple of bits in uncompressed data may not be noticable.
> If the CD is stuffed with large, compressed files with no error
> correction mechanism, a few bits may destroy a lot of data.
 
CD-ROM's are always recorded with an error correcting mechanism.
 
This is as opposed to audio CD's, which lack this error correcting
mechanism.  OTOH if a particular packet of data on an audio CD has
errors, the CD player will just re-play the previous datra packer,
and the listener will in most cases not notice the difference.  Yes,
there is a lot of redundancy in recorded music.  And in the standard
audio CD format, there are 75 packets a second of 2 KBytes each.
 
> Five years may not be unrealistic, depending on what you use, where you
> store it, and how you use it.  Archives of old manuscripts do not, after
> all, maintain special environmental conditions simply because it makes
> the maintainers feel more important.
 
If you're careless with your media, its lifetime may indeed be short.
But if you're careful, it may become quite long.
 
I would suppose that a user which had recorded valuable data will be
careful with that CD - otherwise is't pointless to record it on
that CD.
 
If the data is really valuable, it should of course be re-recorded
every 3-5 years or so.
 
-- 
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Paul Schlyter,  Swedish Amateur Astronomer's Society (SAAF)
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