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punched card

punched card (punch card) A rectangular paper card into which data could be encoded by punching patterns of holes. The holes were then sensed by a punched card reader, which converted the punched patterns into binary code. Punched cards were used extensively for input, output, and file storage of data on early computer systems but are now obsolete.

The cards were of a uniform size and were notionally divided into a number of columns parallel to the short edge and a number of rows – usually 12 – parallel to the long edge. The 80 column card, 7.375 by 3.25 (18.73 by 8.25 cm) in size, was the most common type; each column was divided into 12 positions at which holes could be punched, a particular combination of holes in a column representing a specific character. Cards could be read column by column (i.e. one character at a time), generally at speeds between 150 and 2000 cards per minute, or they could be read row by row, so reducing the time to read a card. The last type of punched card to be widely used was the 96 column IBM card.

Prior to the development of computers a variety of machines were available that enabled the various activities of data processing, e.g. sorting, collating, and listing or tabulating, to be carried out using data files composed of punched cards. Stout cards with holes punched in them were used by Jacquard to control the weaving of patterns on a loom in about 1800. Charles Babbage saw the possibility of using punched cards to control his Analytical Engine, conceived in the 1830s. In the 1880s Herman Hollerith, a statistician at the US Census Bureau, developed a machine that electrically sensed holes punched in cards and could sort and accumulate totals; the machines were used in the 1890 census. In 1896 Hollerith formed his own company, which was later to become IBM.

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