The extent of computer media and/or electronic files may be documented at the collection, series/accession, and folder level as appropriate.
When a collection or series/accession consists solely of digital records, record extent in terms of file storage size and, in some cases, number of files. Though DACS does not offer an example of digital extent recorded in terms of size, the general rule at 2.5.3 seems to allow for it. See also RAD 9.5B2, ISAD(G) 3.1.5 and the Paradigm fonds-level description recommendations, available at http://www.paradigm.ac.uk./workbook/cataloguing/ead-fonds.html. As of April 2010, recent professional practice and recommendations indicate use of gigabytes and megabytes. That said, use the most appropriate file storage size per RAD 9.5B2. For example:
Physical Description: 3.71 megabytes
In accordance with DACS 2.5.7, extent may be further defined through a parallel statement. This could be used to record a large number of files. For example:
Physical Description: 227 megabytes (2,215 files)
Alternately, when the file storage size is not available, describe the quantity in terms of material type(s) in accordance with DACS 2.5.5. See also RAD 9.5B3. This will be the case when some or all formats are unreadable or, in baseline processing, if media has not yet been fully accessioned. For example:
Physical Description: 57 computer disks
Similarly, in baseline processing, when the file storage size is not yet available, qualify the statement to highlight the existence of the material type in accordance with DACS 2.5.6. For example:
Physical Description: 7 folders, including 3 computer disks
EAD allows for multiples statements of extent. When the digital records make up a significant part of a hybrid collection or series/accession, provide two parallel expressions of extent, one for the physical content and one for the digital content. For example:
Physical Description: 4.17’ (10 boxes)
Physical Description: 227 megabytes (2,215 files)