Warning: those irreplaceable CDs won't last forever



A physicist working for International Business Machines Corp. has spread fear and loathing among digital photographers, music fans and others who store data on CDs. His message: The disks we're using to archive photos, album tracks and financial records may turn into useless lumps of plastic after two to five years.

A January Computerworld article quoted Kurt Gerecke, a storage expert in Germany, who warned that the dye that forms tiny pits in the surface of a CD-R can degrade to the point where the laser in a CD-ROM drive can't read them.

How long this takes depends on the quality of the disk and the conditions under which it's stored. Prerecorded audio and data disks, pressed by duplicating machines, don't have this problem. But we certainly shouldn't expect any writable compact disk to last very long, Gerecke said - certainly not the 25 to 75 years that the makers of CDs have traditionally promised. Given the source of the warning, consumers are taking him seriously.

What should you do? I think Gerecke may have exaggerated, but not by a lot. True, plenty of us have five-year-old CDs that still read well. But maybe it's time to think about replacing them.

Here are a few tips for keeping your photos, music and other digital artifacts safe:

Buy brand-name CDs and avoid making backup disks at the highest speed your drive can handle. Disks written at high speed often are harder to read.

Store your backup disks in a cool, dark place. Jewel cases are probably better than sleeves in binders, although there's some disagreement about that. No, you don't have to put CDs in the freezer - in fact, some engineers think that's a bad idea. Just avoid heat and direct light.

Replace your backups every couple of years. It doesn't take that long to copy CDs, and even expensive disks are only half a buck or so. The real investment is your time. Also use write-once CD-Rs instead of rewritable disks (CD-RW), which don't last as long.

For safe long-term storage, consider a magnetic tape backup unit - which Gerecke's recommends for businesses. They start at less than $200 for 20-gigabyte internal models (you'll have to open your computer's case to install one). More money buys higher speed, more capacity or an external unit that connects to a USB or Firewire port and doesn't require messing around inside the computer.

Just remember that tape is a slow and awkward medium. It's not nearly as popular as CDs or hard drives are. So you may have trouble finding a compatible unit to read your tapes 15 or 20 years down the road. Also, while magnetic tape stays good for a long time, it won't last forever, either. Store it under the same conditions as any archival medium - a cool, dry place.

In addition to CDs and tape, consider additional forms of live backup. External hard drives are cheap - $100 to $150 for models that store up to 200 gigabytes of data. A good-sized drive can back up several computers on a home network - and some come with one-touch backup software. Every few years, you can replace the drive. Considering the value of what it's holding, it's a bargain.

Store copies of really important data at another site. As many Katrina victims found out, having a copy of your data on a shelf in your home office doesn't help if your house is completely submerged. Or if there's a fire, or if a burglar cleans the place out. Put copies of critical disks in a safe deposit box, or ask a friend or relative to hold onto a set.

This entire issue, by the way, is an unintended consequence of the digital age. Twenty-five years ago, the longevity of an image, song, or motion picture was tied to the original medium - and there wasn't much we could do about it.

Consider the family photo collection. Over the years, the most popular original photographic media have been Kodacolor negatives for prints and Kodachrome transparencies for slides and home movies.

In the analog film world, that original image - negative or transparency - is always the best one that will ever exist. You've probably seen this if you've tried to copy an old photo without the negative. A photofinisher or desktop scanner can do the job from the print - but it won't look as good as the first print - and will never be as good as a print made from the original negative.

Of course, negatives and slides can fade and change color if they're not properly stored. Now and then, filmmakers also produce substandard materials (many Kodacolor prints from the early 1970s have faded). Still, when my cousin recently had hundreds of old family slides scanned onto disk, I was astounded by 50-year-old Kodachrome images that looked as though they'd been snapped yesterday.

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