Suhit Gupta
04-26-2004, 07:00 PM
<div class='os_post_top_link'><a href='http://news.independent.co.uk/world/science_technology/story.jsp?story=513486' target='_blank'>http://news.independent.co.uk/world/science_technology/story.jsp?story=513486</a><br /><br /></div>"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 lifespan 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."<br /><br />Dutch personal computer magazine, PC Active, has recently investigated this and have shown that some CD-Rs can become unreadable in as little as two years, because the dyes in the CD's recording layer fade. "These dyes replace the aluminium "pits" of a music CD or CD-Rom, and the laser uses that layer to distinguish 0s 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."<br /><br />Does this mean that we should all start rushing out and buying hard drives and making backups of all those CDs that you have burnt? Well, it turns out that "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." Moreover, one thing I was surprised to learn about is that "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 inbuilt 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."<br /><br />Some CD manufacturers still claim to have a 70-300 year life for their CDs but given that we already knew that CDs are particularly vulnerable to scratches, and now with this new knowledge, it might be prudent to save precious data in more than one location (if you didn't know that already :)).