Safe Storage -- for How Long?


By Stephen H. Wildstrom Reader George Wood writes: How long is information, such as pictures, safely stored on CDs that I have burned? I have heard it is only five to six years before they start fading.

All media deteriorate with time, but five to six years is probably far too pessimistic. Verbatim, for example, claims a 100-year usable life for its writeable CD-R disks. The durability of a CD-R (or recordable DVD) depends primarily on the stability of a layer of dye encased within the plastic disk.

Two types of dye are used in CDs -- one gives it a greenish color, the other more of a gold hue -- but there's no solid evidence that either is longer-lived than the other. All dyes are somewhat light-sensitive, so for longest life, keep your archived disks out of the light, particularly direct sunlight.

At worst, optical media like CD-Rs should last a lot longer than magnetic media such as floppy disks or tape, which become demagnetized and eventually unreadable over time. Commercially produced CDs and DVDs, which do not rely on a dye layer, should last the better part of forever, unless they're physically damaged.

RETIRED FORMATS. Probably a bigger risk for durability than the physical media's deterioration is the potential technological obsolescence of the format. I still have some old 5 1/4-inch floppy disks around and even one or two 8-inch ones. I don't know if any of them are actually readable because I no longer have a drive that can handle them.

The same is true for 78 rpm records, video LaserDiscs, eight-track tapes, and many other now-obsolete storage formats. Archivists say the best way to preserve text is to print with a laser printer on acid-free paper. Properly stored, it should be good for 500 years or so -- provided that people still know how to read then.

Wildstrom is Technology & You columnist for BusinessWeek. You can contact him at techandyou@businessweek.com


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