Re: Archival Quality: was benefit of digital camera

From: John <ap@darkroompro.com>
Subject: Re: Archival Quality: was benefit of digital camera
Date: Tue, 13 Apr 2004 22:10:50 -0500

> At 08:30 PM 4/13/2004 -0400, you wrote:
> >When a CD or DVD approaches the end of its useful life and it becomes
> >necessary to move the original digital informaton to some new media, the
> >information itself does not change. Its integrity can remain completely
> >unaltered. It is simply moved to other media. The container changes, but
> >not the information.
>
> Incorrect. File degradation is a fact of file storage. It's
> managed by using CRC checksum validation, Alternate Data Streaming and
> other file backup methodologies. in this regard, digital is just like
> analog in that any reproduction is likely to have some data loss but with
> digital it's usually minimal or complete.

I'm not interested in this thread but I thought to point out that this
is not really true. CD-ROM and most modern digital recording media
make use of very powerful error correcting coding. In the case of
CD-ROM, it uses multiple layers of Reed-Solomon coding with
interleaving to deal with burst errors. These error correcting coding
techniques provide a way to recover original data completely up to
certain errors in the raw (uncorrected) signal due to media
degradation, etc. Some high density tape drives use similar or more
powerful error correction. Some devices do report the host computer
when the media being used has high error rates before correction to
warn the user of the degrading media, prompting to make a complete
duplicate copy of the content before it becomes irrecoverable.

Error correcting coding is much more powerful than CRC or checksum
which only allows detection of errors.

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)