By Lou Dolinar
Updated Feb. 14, 2006

Did this ever happen to you: You've burned a CD, backing up photos, text and other material from your hard drive. You've checked the directory, filed it away, figured it was safe. A month or two later, you try to resurrect the files and surprise, no data.

I've heard two versions of this story in the past week or so, one from a Newsday editor and another from a regular reader. Both are competent with computers.

So what went wrong? A blank CD-R or CD-RW has a shelf life of five to 10 years. CD-Rs, once recorded, are supposed to be good for 50 to 100 years, while CD-RWs should last 20 to 100 years.

Before you blame gremlins, however, consider that those are theoretical numbers, and don't necessarily apply to the real world. As CD-R use has burgeoned and disc prices have become more competitive, poor-quality discs have become a growing problem, according to Bob Smith, an application engineer with Plextor Corp., one of the top drive manufacturers. "The most prevalent problem we experience is when customers try to cut corners on media," he said. "They choose with their pocketbook rather than project in mind. With the lowest-cost media, they're not necessarily going to get the results and longevity they expect."

True, there are genuine bargains, but you may also hit a batch of discs that should have been rejected by the quality-control department. Cheap discs work well enough for music CDs, with an occasional pop and click as the only symptom. But similar defects on a data disc can render it unreadable - if not immediately, then in a matter of weeks or months.

Plextor and other manufacturers generally test and publish detailed lists on their Web sites of suitable media for specific drives - faster-recording drives, for example, will usually require higher-quality media. Smith says that once you've found a brand that you like, stick with it.

If technical specs float your boat, see the CD-R FAQ (www.cdrfaq.org), which notes, "The manufacturers claim 75 years (cyanine dye, used in 'green' discs), 100 years (phthalo-cyanine dye, used in 'gold' discs), or even 200 years ('advanced' phthalocyanine dye, used in 'platinum' discs) once the disc has been written."

But we're just trying to get through the next couple of years, and there are more immediate issues. Improper handling also can trash a disc. Tossing a CD-R in the drawer, without a jewel case or sleeve, often scuffs and scratches a surface and renders it unreadable. Leave it on a desktop, and sunlight and heat can damage the dye layer that's used to record data. Overheated parked cars aren't the best environment, either.

And then, of course, there's the usual gamut of catastrophic events - fire, flood or simply stepping on the disc. Even though you've been handling music CDs for years, keep in mind that recordable media are a lot more sensitive to abuse than factory-burned discs, and rewriteable CDs potentially have more problems than CD-Rs. High-density DVDs are less tolerant of abuse than CDs. In general, for storage, think cool, dark and dry. If you plan to use the data disc regularly, most experts also recommendmaking one "use disc" and another copy as an "archival disc."

Improper labeling is our last big culprit in CD failure. Smith says that if a label is applied slightly off-center, it may create some wobble as the disc is read, causing the drive to drop data.

John Christopher, an engineer at the data-recovery firm Drivesavers in Novato, Calif., says he also sees a lot of discs that have been damaged by adhesives from labels. Pens, unless they're specifically rated for use with recordable media, may also damage CD-Rs.

A precaution that Christopher recommends: Verify that your files have actually been written to the CD by opening and reading them. Software often breaks down during writing. He's seen a fair number of discs that superficially appear perfectly normal but where the software has written a directory of the files there are no files. Another possibility: The files may be there, but since the disc wasn't closed properly, ordinary software can't open them from the directory.

Finally, keep in mind that CDs and hard drives organize your data quite differently. While a hard drive can fail catastrophically, more often it degrades first: The magnetic structure weakens, and parts of files become inaccessible. Traditionally, computer operating systems include software tools like chkdsk to detect, correct, map out and repair these kinds of flaws.

You won't find CD-repair tools like this as part of Windows XP, because CDs, at least potentially, are more robust. But as we've found, CDs can fail, and organize data in a way that when one section of the disc fails, it takes everything with it. Next week, we'll look at tools and techniques for reviving these failed discs.