The holdings of one library may be duplicated in whole or in part by the holdings of another. If a book is lost or stolen it probably can be replaced. Archives collect original unpublished material or primary sources. Since archives collect any medium that records information, the format of collections may be diverse and may include letters and diaries, photographs, maps, architectural drawings, computer tape, video and audio cassettes. The size of a collection may range from a single document to hundreds or even thousands of metres of material.
Archivists distinguish between record groups and manuscript groups.
A record group would include the various media created as part of its activities by a business, government or other institution. The principle of provenance requires that the archives of an organization or person not be mixed or combined with the archives of another. If, for example, the administrative office of a religious denomination maintained files alphabetically by name of congregation, that order would be maintained or, if necessary, reconstructed by the archives. National Archives of Canada. For these reasons, archives are vital to maintain the specific detailed information that would otherwise disappear or be forgotten.