> > I guess "grey bits" never caught on. "Grey bits" were a
> > copy-protection mechanism in which parts of the original media a
> > program is distributed on were encoded poorly, so that repeated
> > reads of the grey sections would produce different results. Before
> > running, the program would try to read the grey section until
> > something came up different.
>
> So it wouldn't work if played on an excellent high signal-to-noise
> ratio reader ? :-)
The transducer that reads the data from the media has a signal-to- noise ratio (digitally, this means an error rate) which is independent of the S/N ratio of the reproduced signal.
Take a conventional silver CD. If you were to make the pits containing the "grey data" extra small, sometimes you'd read them correctly and sometimes you wouldn't. As the "grey data" is not part of the signal reproduced, the user application isn't aware that they're not being read consistently. A copier running at user application level would thus make an identifiably imperfect copy, though the actual user data content would be accurately reproduced.
The "grey data" bits would have to be interleaved with normal data so as to avoid loss of tracking.
This is an example of the sort of "copy protection" I find acceptable, because I can make as many perfect copies as I like for my own use; nonetheless the copies can be identified as such, for the purposes of prosecuting anyone who happens to be trading them in place of genuine original pressings.
Regards Brian Beesley _________________________________________________________________________ Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
