CDs and DVDs are frequently regarded as safe ways to back up precious files and memories. However, given the short time they have been available, there is some concern that data may not last in the medium-to-long term. This month I'll be looking at some of the ways you can help give added life to your CD and DVD collections.
When audio CDs were launched in the early 80s, they were frequently marketed as robust and 'indestructible'. This was demonstrated with the CDs being exposed to brief blow-torch and Frisbee demonstrations. Sadly, the early hype had more in common with calling the Titanic unsinkable than the reality users have since experienced. Everyone has probably encountered a damaged optical disc, but knowing the causes can help prevent catastrophic failures.
CDs were developed with some thought given to the possibility of damage to the disc. Bubbles in the plastic and minor scratches were likely to destroy the data, so a technique known as error-correction was introduced. The details of the process are quite complex, but the upshot is that if a CD sustains minor damage, the error correction technology can help determine the value of the lost or unreadable data. Since the disc needs to store this error correction as additional information, it makes storage less efficient. A balance was then struck between the amount of damage a CD could receive and the total data it could store.
This error-correction technology can lead some people towards complacency - scratched discs can still work, but once you cross a certain threshold, you can kiss the data goodbye. As you'll see in the rest of this column, there are plenty of nasties that can attack your CD. In general, one type of light damage may have little impact, but in combination the errors can trash your disc.
It sounds obvious, but your discs should be kept in pristine condition and it's imperative to avoid scratches at all costs. Never put a disc directly on a hard surface, even for a moment (this includes both sides). As you put down and pick up the disc, dust and small traces of grit can damage the surface. My solution to this problem is to grab a single CD jewel case and remove the top cover. The bottom section now provides a simple place to drop a CD if you can't immediately find its case. Keep one next to each computer or DVD player.
Another common problem is the issue of fingerprints. Ideally you should handle the disc from the edges and centre spindle. This can be tricky for small kids' hands and some sufferers of arthritis, who also face dexterity problems. In these cases, try using backup copies or regularly clean the discs. For about $5-10 you can buy a CD cleaning kit and, when a disc is dirty, use it! Shirts, blouses, fingers, buttocks and pieces of furniture are not suitable alternatives. These will scratch the surface and frequently add grit and smear the greasy marks, rather than remove them. Also avoid the temptation to blow on the surface. Small droplets of saliva will be sprayed onto the disc. When dried, the small dollops can block the laser and may help provide food for certain types of organisms that would love to eat into your collection.
If you want your CD or DVD to last, then don't use a sticky label. In fact, the US-based National Institute of Standards and Technology (NIST) advises that "Adhesive labels should not be applied to optical discs destined for long-term storage (more than five years)." The NIST has a long list of reasons why labels are bad for CDs. Here are some: the adhesive can react with the top lacquer layer and the labels can cause instability and add to the wear on a CD drive. The labels can also - here's a great Americanism - 'delaminate'. This minor lifting of the label can unbalance the disc or, in the worst case, dislodge inside the drive and make the entire unit cactus.
If your discs currently have paper labels, don't attempt to remove them - it'll make things worse. Instead, copy the contents to a new disc and avoid using the old one. So what can you use to label a disc? It may not be as attractive, but the way to go is to use a solvent-free permanent marker. Smaller tips are easier to use, and be sure the CD is sitting in a case when writing the label - don't place it on a hard surface.
With all due respect
CDs will last longer if they are kept upright in a cool, dry place away from the sun. The NIST recommends storing CDs under 20 degrees and between 20-50 per cent humidity, but there are not many places in Australia where this would be possible. The key points are to use a cool, dark storage area. Finally, the most important thing to remember is that CDs and DVDs are fragile. They'll be the storage area for your precious photographs, files, e-mails and documents, so treat them with care.
The Web site belonging to the US-based National Institute of Standards and Technology (NIST) contains a wealth of information for industry researchers and casual browsers alike. If you want to know more about the institute's recommendations for the care and storage of your precious optical discs, use the report number 500-252 in the site's search engine, and the relevant publication (as a downloadable PDF) will be at the top of the results list.
Admittedly, some of the articles are a little obscure for general consumption; take 'A safer way to make Nanospheres' for example. But if you want to keep an eye on the cutting edge of science, put this on your list of favourites.
Formats for future-proof Files
The explosion of file formats will create headaches for everyone in the future. The crucial problem is that each file type needs a program to open it, and programs, in turn, need operating systems. To make things really messy, some bonehead developers introduce incompatibilities between versions of their software, so that you need a matching version of the software to open a particular file. Now, what if that program won't work on your current operating system? XP users have experienced the pain of DOS programs that will no longer run. No one knows what the compatibility of operating systems will be like 20 or 30 years from now, but you can bet it won't be good. Without a way to run the software, you won't be able to access files unique to that program.
If the file is important, I suggest making copies in several formats - and try to steer away from files linked to only one program. For documentation, this translates to: your original, plus a PDF and txt file version (or CSV for spreadsheets). JPEG looks like the front runner for graphics, but use the best quality setting. Despite a range of alternatives, MP3s still remain a compact and popular standard for audio files. However, creating exact copies of your audio CDs is the safest, albeit most laborious option. Thanks to the explosion in popularity of home DVD players, MPEG-2 is probably the most compact and future-resistant video format (for the time being).
A fungus ate my CD
In recent years there have been several reports of micro-organisms destroying CDs. According to the publication Nature, one species of fungus was discovered attacking the all important aluminium/data pit substrate of a CD. The report notes "Burrowing in like worms from the side of the disk, the fungus destroyed crucial information pits." For more details, head to www.nature.com (search for 'fungus eating CD').
Taking this to the next level, Cameron Jones, an Australian researcher and DJ, used fungus to create new music. By deliberately infecting audio CDs with the Penicillium fungus and incubating the CDs, he was able to alter the sounds produced by a standard disc. The fungus changed the behaviour of the laser as it bounced through the various layers, creating chaotic alterations to the sound, including pitch changes and staccato rhythms.
Incidentally, he discovered this technique when handling CDs with hands that were wet with beer (another reason to keep your CDs clean). For more information, head to www.swin.edu.au/chem/bio/fractals/refslist.htm.
Click here to view a screen shot of penicillium fungus growing on a CD-R. Image used with permission, courtesy of Cameron Jones, Swinburne University of Technology.
Scott Mendham has been writing for PC World and producing the cover CDs for over six years. During this period, he has authored an alarming number of books on a wide range of IT-related topics, and will freely admit that his first computer was a TRS-80.