What is "aperture card"

An aperture card is a type of punched card with a cut-out window into which a chip of microfilm is mounted. Such a card is used for archiving or for making multiple inexpensive copies of a document for ease of distribution. The card is typically punched with machine-readable metadata associated with the microfilm image, and printed across the top of the card for visual identification. The microfilm chip is most commonly 35mm in height, and contains an optically reduced image, usually of some type of reference document, such as an engineering drawing, that is the focus of the archiving process. Aperture cards have several advantages and disadvantages when compared to digital systems. Machinery exists to automatically store, retrieve, sort, duplicate, create, and digitize cards with a high level of automation. While many aperture cards still play an important role in archiving, their role is gradually being replaced by digital systems.