Data stored on CD disk drives begin to degrade within a few years. Unless provisions are made to move data from one storage medium to another, the data are lost relatively quickly. Of course, if data are judged to be valuable to a research community, resources can be devoted to replication so as to minimize the risk of digital media decay. As generations of applications, data formats, operating systems, and digital archives interoperate and succeed one another, multiple locations and systems for data access and sharing might be engaged to preserve a given data collection. Ensuring that archived data are not altered due to human error or intentional mischief is an additional challenge for large data repositories, particularly those utilizing automated processes to ingest large datasets.6Table 4-1 shows the various risks to long-term digital data reliability and the time frames in which they might be expected to occur.
National Research Council. 2005. Building an Electronic Records Archive at the National Archivesand Records Administration. Washington, DC: The National Academies Press. See Chapter 4 in particular.