Re: [ARSCLIST] Preservation media WAS: Cataloguing still :-)

[Jerome Hartke <jhartke@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:ARSCLIST@xxxxxxx] On Behalf Of Mike Richter
> Sent: Saturday, September 02, 2006 8:33 PM
> To: ARSCLIST@xxxxxxxxxxxxxxxx
> Subject: Re: [ARSCLIST] Preservation media WAS: Cataloguing still :-)
> 
> steven c wrote:
> 
> > Well, there is an upper limit to the accuracy of any analog data-storage
> > technology...if nothing else, the molecular qualities of storage media
> > define a limit (albeit a VERY large one!). In fact, I would suppose this
> > would also apply to digital media?!
> 
> Digital media incorporate error correction in order to reduce the
> probability that an error will affect the result. In fact, the raw error
> rate of digital recording tends to be very high, but layers of ECC
> reduce it essentially to whatever resulting rate is acceptable.
<snip>
Optical media raw bit error probabilities are typically a few per million
(ppm) for good discs. This is very low. ISO limits are 58 ppm for DVD and 70
ppm for CD.  There are lots (hundreds of thousands) of raw errors on a disc
because there are trillions of bits. Error detection and correction normally
reduces the read error rate of data to the host to zero. Of course, bad
discs or drives can and do cause problems, similar to attacking a tape with
scissors.

Jerry
Media Sciences, Inc.