s gaining a stronghold. Given the history of technology, we can only assume that any given method of storing information will be transient, and the cycles of life expectancy for any given format may even become shorter as time goes on.
Another problem revolves around the various file formats used to store information and the software used to create and view these formats. The way that text, images, sound, and video can be stored and accessed by computers has gone through many transitions. The software involved with creating and viewing digital information evolves rapidly, as do the hardware platforms and operating systems involved. Word processors, graphics programs, and video editing environments evolve quickly, and there are no guarantees that each new version will be backwards compatible with previous versions.
Digital media fall prey to physical deterioration. It is a common misconception that once recorded onto standard media, that digital information will last forever. Magnetic tape, optical discs, and hard disk drives all have limitations on how long their data will last if left unattended. Some CD-ROM manufacturers claim life expectancies of 200 years without data loss. But such assertions are not undisputed and environmental conditions can definitely accelerate deterioration. Optical media generally offer longer life than magnetic, but neither approaches the ideal of permanence. Yet, the real problem is obsolesce rather than deterioration. Even if the data were to stay intact on the media for 200 years, would there be playback equipment available? Given the rapid change in hardware already noted, it seems highly unlikely that compatible equipment would exist.
I don't intend to paint a negative picture regarding the long-term viability of digital information. My point is to show the challenges that must be met. Strategies, methodologies, and technologies for preservation are being developed and refined, and are a key component of any digital collection.
Basic methods for preserving digital content
The long-term preservation of digital material requires a commitment to an ongoing set of processes to move digitized materials through each generation of technology. A strict adherence to all appropriate standards will increase the likelihood that digital objects will migrate into the next generation with the least loss of content, greatest efficiency, and the lowest cost.
We know that there is no permanent and durable medium for storing digital information. This leads to the need to test and refresh information at appropriate intervals. Copying data onto fresh media can re-start the life-expectancy clock. If, for example, we assume that a CD-Recordable disc will last for 20 years, burning a new copy every 10 years would be a process that could be followed to preserve the data, given an assumption that this media continues to be viable.
New media options continually emerge, with each successive generation offering more capacity at a lesser cost. Given this trend, it's likely that in most cases information will not be refreshed onto the same type of media, but will be moved onto the next generation. It wouldn't make sense, for example to refresh data held on 3 ½ inch diskettes onto the same kind of media. Rather, it would be more practical to copy the data onto CD-ROM or DVD.
Many digitized collections reside on online storage systems of some sort. These devices offer instant access to information, are highly reliable, and can be built for very large capacities. Yet we do not expect any given online system to last forever. Storage systems typically last 3-5 years and are replaced by faster and better ones. Online storage systems become obsolete very quickly. Cycles of migration of data in the online storage arena can be very short. These systems are also volatile. It's important to follow strict data management and disaster planning procedures to ensure that systems failures do not result in loss of information.
One of the most important strategies related to digital preservation involves taking advantage of open standa