|Re: Reading the New HP Museum DVD disks|
Message #13 Posted by James M. Prange (Michigan) on 7 Aug 2007, 8:35 a.m.,
in response to message #11 by Dave Shaffer (Arizona)
True for CDs, but not for DVDs.
The information on the disk is actually encoded just below the printed side, i.e. on the top side of the plastic disk material just below the printed label.
Assuming single-sided DVDs, you'd have to have damage (from the "label" side) more than half way through to affect the data on a single-layer DVD, and almost half way through to affect the data on a dual-layer DVD.
For some diagrams of the physical structures of DVDs, see http://www.divxland.org/dvd_formats.php or chapter 3 page 3 of http://www3.toshiba.co.jp/dvd/e/whats/index.htm.
I believe that the HP Museum version 6 DVD set is one DVD-9 (single-sided dual-layer) plus one DVD-5 (single-sided single-layer).
The direction of a scratch makes a big difference. If the scratch is radial, then there's a good chance that between the data interleaving and error correction codes, the disc drive will be able to correct the errors. If the scratch is tangential, or worse yet, parallel to the track, then too long of a stretch of data may be corrupted to make a correction. If you try to polish out a scratch, then be sure to rub radially. For polishing, Brasso or NEVR-DULL metal polishes seems to work well, although some mildly abrasive toothpastes should work, and there are products marketed specifically for CDs and DVDs.
Edited: 7 Aug 2007, 8:49 a.m.