A card image is an archaic term for an ASCII string, usually 80 bytes in length. It refers to a Hollerith card, a data storage medium popular in the 1960s and 1970s. Two standard sizes of Hollerith card stored 80 or 132 characters. A single card was typically used to store a single line of text, for example a line of FORTRAN code. Many data formats, such as the FITS image file format, still use card images as basic building blocks -- even though physical hollerith cards have not been widely used since the advent of inexpensive disk drives in the 1980s.

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