Punch card

The punch card (or "Hollerith" card) is a recording medium for holding information for use by automated data processing machines. Made of stiff cardboard, the punch card represents information by the presence or absence of holes in predefined positions on the card. In the first generation of computing, from the 1920s into the 1950s, punch cards were the primary medium for data storage and processing. Eventually the punch card would be phased out and replaced with huge floppys for media storage, for loading data, in the late 1970's, early 1980's.

Key punches

Data was entered on a machine called a keypunch, which was like a large, very noisy typewriter. Often the text was also printed at the top of the card, allowing humans to read the text as well. This was done using a machine called an interpreter. Later model keypunches could do this as well. Multi-character data, such as words or large numbers, was stored in adjacent card columns known as fields. For applications in which accuracy was critical, the practice was to have two different operators key the same data, with the second using a card-verifier instead of a card-punch. Verified cards would be marked with a rounded notch on the right end. Failed cards would be replaced by a key punch operator. There was a great demand for key-punch operators, usually women, who worked full-time on key punch and verifier machines.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Electromechanical equipment (called unit record equipment) for punching, sorting, tabulating and printing the cards was manufactured. These machines allowed sophisticated data processing tasks to be accomplished long before computers were invented. The card readers used an electrical (metal brush) or, later, optical sensor to detect which positions on the card contained a hole. They had high-speed mechanical feeders to process around one hundred cards per minute. All processing was done with electromechanical counters and relays. The machines were programmed using wire patch panels.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~