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Archival descriptions of the permanent holdings of the federal government in the custody of NARA are stored in Archival Research Catalog (ARC). The archival descriptions include information on traditional paper holdings, electronic records, and artifacts. As of December 2012, the catalog consisted of about 10 billion logical data records describing 527,000 artifacts and encompassing 81% of NARA's records. There are also 922,000 digital copies of already digitized materials.

Where are archival descriptions of holdings under the custody of NARA stored?
Archival Research Catalog (ARC)