Aperture card

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Used in data archiving, the aperture card is a small, simple piece of punched card-stock paper with a slip of microfilm appearing within a window in the card. The punches in the card, like a conventional punched card, contain data that a machine can rapidly read to aid in locating a particular card or for obtaining information from a selected card. The microfilm component contains an optically reduced image, usually some type of reference document, that is the focus of the archiving process.