Ready for a digital dark age?
Consider the BBC Domesday Project, undertaken in 1986 to mark the 900th anniversary of the original Domesday Book, a land-use survey of England commissioned by William the Conqueror in 1086. For the latter-day survey of the island, thousands of Britons contributed text, photos and video that were published on two custom laser disks.
But just 15 years later, it was impossible to access those disks without lots of custom hardware and extensive software emulation. Currently the Centre for Computing History in Haverhill, England, has a functional emulation and hopes to post the contents to the Web.
Meanwhile, the original Domesday Book, handwritten on sheepskin, remains in the British archives, usable after nine centuries by anyone literate in Latin.
Anyone with data stored on 5.25-inch floppies or text in WordStar format faces a problem similar to the one that befell the BBC Domesday Project. The digital data we are generating wholesale will very likely become unusable within our lifetimes unless we take steps to preserve it.
The situation cannot be blamed entirely on the computer industry's treadmill of planned obsolescence. In essence, digital storage technology has inherent drawbacks that make paper look immortal.
Data mortality
A hard drive removed from a computer and left on an office shelf will eventually become unusable just because of daily temperature changes, explains Tom Coughlin, a data storage consultant in San Jose. The thermal energy fed into the media will gradually trigger spontaneous reversals of the magnetic particles that store the information, until the original data is lost, he explains. However, the loss should not be a problem for the first 10 years, he adds. After that, it's anyone's guess as to when the data becomes unusable.
Magnetic tapes have the same problem, but take decades to lose data to thermal erasure because they have a lower bit density than hard drives, Coughlin says. On the other hand, tapes have a different problem: delamination, which is what happens when the magnetic media separates from the tape or is attacked by fungus. Tapes sometimes have to have their media re-affixed with a baking process to allow the one final read needed to move their contents to another medium, Coughlin says.
USB memory sticks are also subject to thermal erasure and face added risk because they typically have the cheapest available controllers. "I would not use them for archival purposes," he says. Continued use of USB memory would also require that USB ports still be in use decades from now, and it's anybody's guess what laptops will look like in 20 years, let alone 50.
As for DVDs and CDs, Bill LeFurgy, a project manager at the Library of Congress, reports that his organization has done accelerated aging tests on them using ovens and has found enormous variability among discs -- even among those that are the same brand. "Some will last a decade and others much less," he says. "Beyond five years, I would be nervous."
Other storage professionals complain that the throughput of DVDs is too slow for archival use. DVD throughput is typically less than a quarter of tape throughput, plus DVDs have to be changed every few gigabytes.