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This section addresses various practices that have been, or might be, used to preserve digital information and to preserve access services to digital information. It uses the functional and information modeling concepts described in subsection 4.2 and applies them to these practices, and it extends the terminology to distinguish significant aspects of these practices. There will be a number of options available to preserve any particular piece of digitally encoded information; the particular preservation solution applied should be chosen to match the requirements identified in the interactions between Administration and Preservation Planning.

The fast-changing nature of the computer industry and the ephemeral nature of electronic data storage media are at odds with the key purpose of an OAIS: to preserve information over a long period of time. No matter how well an OAIS maintains its current holdings, it will eventually need to migrate much of its holdings to different media (which may or may not involve changing the bit sequences) and/or to a different hardware or software environment to keep them accessible. Today’s digital data storage media can typically be kept at most a few decades before the probability of irreversible loss of data becomes too high to ignore. Further, the rapid pace of technology evolution makes many systems much less cost-effective after only a few years. Even more daunting, as operating systems evolve, is maintenance of operational software as a part of the Representation Information, which means that it is essential for the preservation of Content Information. In addition to the technology changes there will be changes to the Knowledge Base of the Designated Community which will affect the Representation Information needed.

Fundamentally, approaches to information preservation in the face of changing technologies and Designated Community requirements require digital migration as it is defined and addressed in section 5.1. Digital migration of an AIP can include:

– copying Content Data Object or Representation Information bits to new media

– altering or adding to Content Data Object or Representation Information bits

– altering or adding to PDI bits

– altering or adding to operational software whose role is essential to Content Information preservation (i.e., it is part of Representation Information)

– altering or adding to the bits that make up the AIP’s Packaging Information

Subsection 5.1 discusses digital migration in general terms; subsection 5.2 then discusses in more detail the roles of software both simply as a convenience for access to Content Information and as a key component of the Content Information.

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