Larry sez:
>> and you're replacing/refreshing your data
>> once every 5 years,
> >you're going to go through 15 cycles.  And the
> >process is NOT
> >"lossless".  No one has come up with exact figures
> >as to how much loss is
> >acceptable, but it's not uncommon to experience
> >1-2% loss per migration...

And, Dan opines:
> I couldn't let this go
> unchallenged (despite your
> other good points.)  It is inaccurate to state that
> digital conversion is
> not lossless and grossly inaccurate to say that
> there is a "1-2% loss per
> migration".

It's also grossly inaccurate to mis-portray what I
said =)

I said  "No one has come up with exact figures as to
how much loss is
acceptable, but it's not uncommon to experience 1-2%
loss per migration..."

To date, no one HAS come up with the figures IN A
PUBLISHED STANDARD OR REPORT that tells what the loss
expected is, and I have to think that's because no one
really knows.  NML doesn't have one, CD Freaks says
it's MUCH higher than I stated... and for the record,
I didn't say that you will definitely experience a
1-2% loss, I said "it's not uncommon to experience"
which means it happens, and sometimes it's higher.

(snipped for brevity)
> If you use CD's  - which are less reliable than a
> standard magnetic disk
> but more reliable than non-DAT magnetic tape over
> short terms - but the *uncorrected*
> bit error rate is about
> 1 in 10^(-12) or one per trillion bits.   The math
> works out pretty even so that the changes of a
> single meaningful pixel
> change are just under 1 in 10 trillion.  Hardly a
1-2% loss.

While this was all very informative, I don't know too
much about what it has to do with reality.  Ever make
a copy of a CD on a typical PC or MAC?  Ever make a
copy of that copy? How about a copy of that copy?
Always get an accurate representation?  I haven't.

But the issue here is a CD was originally produced
from a (presumably) hard drive and it was stored for 5
years.. then the contents were loaded back onto the
hard drive, and back to a new CD and 5 years later,
the process was repeated.  Okay, so data has moved 5
times now to make this 3rd generation CD... now I
think everyone remembers what CDs were like 10 years
ago (1994)?  They were designed for a slower write and
read rate, they were expensive and most of the ones
you copied data onto then are sort of difficult to
read now.

As Dan mentioned in his first post, who has a 5-1/4"
or even a 3-1/2" drive anymore?  Who has a 4x CD
drive?  Now, after this 3rd migration, the likelihood
that what we know as CDs being the "media de jour" any
longer is pretty limited, so we'll be moving this data
to a hard drive (?) and then to some new form of
media... and so on and so on, which is closer to the
scenario Jesse presented about the floppies and zips
to CDs and why I stated that the potential for loss is
greater than most organizations are willing to accept.


The media vendors limit themselves to the replacement
of media as a liability, and that's only if you
properly maintained the media in accordance with their
instructions.  Is this because of how stable it is? I
don't think so.

I'm not talking about 3-7 year data here, I'm talking
about 50-75 year data, or data required "for the Life
of the Republic"... and it's not a huge percentage of
what's gathered annually, but it's worth protecting
better than with the available disposable media.

I'm afraid some may have misunderstood my post as
acall to film rather than find a better means of
capture and management of electronic data, and that's
not the case... I'm just saying that there are cases
where the present media isn't good enough, and film is
a better alternative.

Larry

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