While reading some of Ken Rockwell's excellent articles on photography, I came across a tidbit of information - something I actually hadn't thought about before, but that should be noted by people using DVDs to do data backups:
DVDs were never designed with the error correction levels of CDs and I've heard people who know warn against them for data archiving. We designed the DVD for MPG video where we can loose data; we realized the CD was overengineered for audio and wasted too much data on redundancy for error correction. We fixed that in the DVD making it less suitable for data files but better for releasing movie rentals.See also HowstuffWorks: DVDs:
KenRockwell.com: How to scan 3000 slides
On a CD, there is a lot of extra information encoded on the disc to allow for error correction -- this information is really just a repetition of information that is already on the disc. The error correction scheme that a CD uses is quite old and inefficient compared to the method used on DVDs. The DVD format doesn't waste as much space on error correction, enabling it to store much more real information. Another way that DVDs achieve higher capacity is by encoding data onto a slightly larger area of the disc than is done on a CD.
Anders Jacobsen |