CD deterioration project

[deb_bogard]

Hello! I have a student who is interested in studying how CDs may deteriorate under lights, humidity, etc. and start to lose data. Is there freeware available for him to utilize that would be able to detect data loss - like bit-level errors? I'm not computer-savvy enough to know what to look for. Many thanks in advance for your advice.

[barretttomlinson]

Hi,

You might be interested in this study, though it is not directly responsive to your question:

http://www.mscience.com/longev.html

Here is a google book review on data restoration;

http://books.google.com/books?id=SNoNlm ... #PPA449,M1

I am not aware of any freeware CD inspection tools. Here is an advertised product that may have a free demonstration period (Neither I nor ScienceBuddies recommends nor endorses this product or company!!!) that might possibly fit your need. I have no experience with it.

http://www.infinadyne.com/download.shtml

It appears that disk readability is a complex matter, depending on both CD reader/writer, and the disk itself. Error detection and recovery are built into the recording format, so that fairly extensive degradation of the disk must occur before the disk becomes unusable. This all appears to be a rather complex subject, and I can claim no expertise in it.

I hope this nonexpert reply is useful to you, despite its limitations, and wish you every success in your pursuit of this matter.

Barrett Tomlinson

[deb_bogard]

Thanks for your response and your suggestions!

[sunbeam]

This sounds like an interesting project!

Barrett is right that CDs have built-in error correction coding. From the wikipedia entry on Compact Disc, I read that in 588 bits of storage, only 192 are the actual file, and the rest of the bits are correction coding / control / synchronization bits.

However, it would still be interesting to see how much beating the CD can take before there are errors in the file. Here's one idea for how this could be approached.

You can take a large file-- perhaps by zipping up a bunch of music or photos-- and burn it onto several of the same kind of CD. Leave the original file on your computer. Then subject the CDs to various amounts of damage Then insert the CD back in the computer, and use some kind of binary file comparison software to compare what you get. Because of the coding on the CD, it won't be a bit-by-bit check of what's actually on the CD-- it will be a bit-by-bit check of what the computer was able to read from the CD.

In order to compare the files, you could possibly find some software online. I did a search for "compare binary files," and I didn't find anything spectacular but there's got to be something If you have a mac or linux computer, you can open a terminal and do the following.

Say we have two files, File1.zip and File2.zip. I will use the character '>' as a prompt. We can type:

> diff File1.zip File2.zip

Then when you hit enter, if it just returns to a prompt that means the files are the same. Otherwise it will say "Binary files File1.zip and File2.zip differ."

Now if you want more information-- like where they differ-- that is a little harder with binary files and I'm not totally sure how to do that. Others will be able to chime in more here. You could convert the binary files to hex with

> od File1.zip > File1Hex
> od File2.zip > File2Hex
> diff File1Hex File2Hex

but I don't think the output will make it very easy to see exactly where the problems are. In this case, diff will return sections of File1 and File2 which differ, but you would have to look line by line to see where the difference is. You could make this easier by using an ascii file (that is, a text file with characters and not binary data) to burn onto the CD... but it's not easy to find a 700 MB ascii file

Good luck and have the student write in if he goes ahead with it!
Laura

[deb_bogard]

Wow. I'm starting to get the idea now. This really could be a great learning experience...for me, too!

[ChrisG]

Hi,
I think this might do the trick
http://www.vanheusden.com/recoverdm/
(see the -l option)

You also might be able to use this:
http://www.isobuster.com/isobuster.php
I used that program for a data recovery project and the software author was very helpful and responsive. I don't know if there is still a "demo" version of the software. Maybe he would be willing to donate to a worthy

Another one with a "demo" version
http://www.atrise.com/fbi/

Good luck!
Chris

[deb_bogard]

Thanks for all the links - they've really been helpful!