The Myth Of The IOO-Year CD-ROM

From: The Independent - UK 4-21-4  

Are we putting too much faith in the ubiquitous "Recordable CD", or CD-R? It is undeniably one of the most useful means of storage around, offering an inexpensive way to save digital photographs. music and files and costing less than 50 pence per disc.  

If you check the claims made by some manufacturers of popular CD-R brands, you will see that some make bold claims indeed. Typical boasts include: "100-years archival life", "guaranteed archival life- span of more than 100 years" and "one million read cycles". One company even says data can be stored "swiftly and permanently", leaving you free to bequeath those backups of your letter to the electricity company to your great great grandchildren.

But an investigation by a Dutch personal computer magazine, PC Active, has shown that some CD-Rs are unreadable in as little as two years, because the dyes in the CD's recording layer fade. These dyes replace the aluminum "pits" of a music CD or CD- RAM, and the laser uses that layer to distinguish Os from 1s. When the CD is written, the writing laser "burns" the dye, which becomes dark, to represent a "1" while a "0" will be left blank so that if the dye fades, there's no difference; it's just a long string of nothing to the playback laser.

So have you already lost those irreplaceable pictures you committed to the silver disc? PC Active suggests we should forget CD-Rs as a durable medium, after its own testing found some with unreadable data after just two years. "Though they looked fine from the outside, they turned out to be completely useless," wrote the technical editor Jeroen Horlings, who had tested 30 brands in 2001, left them in a dark cupboard for two years and then re- tested them in August 2003. Of the brands tested, 10 percent showed ageing problems.

Recordable DVDs are not off the hook either. The "dye chemicals" in write-once DVDs are similar to CD-R, though recording density and disk construction differ. "We're in the process of testing DVDs and we're sure that the same problems will occur," said Horlings, who plans to publish his findings soon.

In the wrong conditions, such as sunlight, humidity and upper surface damage, your CD-R will slowly turn into a coaster. "CDRs should never be left lying in sunlight as there's an element of light sensitivity, certainly in the poor quality media," says Stevenson. "I wouldn't rely on CDRs for long-term storage unless you're prepared to deal with them as recommended."

Such views are echoed by the National Archives at Kew. "Generally speaking, we don't recommend CDRs for long-term storage," says Jeffrey Darlington, a project manager at the Archives' Digital Preservation Department. 'We don't regard CDRs as an archival medium. Most of the CDRs on the market are not of archival quality.

Not all optical media is vulnerable. The rewritable variants (RW) use metallic materials that change the phase of the light, rather than light-sensitive dyes. Commercial magneto-optical and ultra-density optical systems are different too.

Vane-Tempest also offers a tip. Blank CD-R disks have a code that your CD writer reads to find the best writing strategy. If this isn't in the CD-writer's software (its "firmware"), the default may be a poor compromise. Vane- Tempest says that some "less scrupulous" Far East companies have been using other people's codes, with deficient results. However, there is a way around this which is to find out which brands suit your writer and ensure the firmware is up to date.

As the oldest CD-R is barely a teenager, there are no definitive answers either. But perhaps the last word belongs to Jeroen Horlings at PC Active, "We see a lot of manufacturers and they think that quantity is more important than quality,., he says. "The problem will remain,".'


@ 2004 Independent Digital (UK) Ltd