Card catalog           

The original purpose of the card as a cataloging tool was to aid in material retrieval by the user, to make access points available from the descriptions on the card, to determine the title, author and subject of the work, and to establish authority control. This was a long and cumbersome process, which required all holdings of libraries to be cataloged (usually by hand) one by one.

Libraries could use card catalogs for shared cataloging through union catalogs, usually in book or microfilm form. These union catalogs were made up of copies of the card catalog record for each item in the library. Union catalogs were not realistic for most libraries to own because they were expensive to create, difficult to update, and often cumbersome to use.