A piece of stiff paper that can contain digital data represented by the presence or absence of holes in predefined positions. Punched cards were used for processing digital data and to control automated machinery. Early computers utilized punched cards as the principal medium for input and output. In “The Fun They Had,” the children enter their homework into their mechanical teachers so that the computer can calculate their score. Margie has to write her homework out on punch code, which she had to learn when she was six years old. Although the punch card is anachronistic to contemporary computers and therefore the future, it was very popular in the age of early computers, when Asimov was writing the story.