Punched cards, or punchcards, were for many years the major method of providing input to computers. Programs in FORTRAN or COBOL or RPG were punched onto decks of cards (one card per program line) on keypunch machines and handed in to be run in batch-processing mode on the computer, which was too massive and expensive to be made available to individuals other than through the mediation of system operators who eventually handed back the output in printed form. Often the function of the programs was to churn through large amounts of data to do number-crunching or other operations on it; this data might also be provided on punchcards (though magnetic tape and paper punched tape were also used). Punchcards could also be found in all sorts of other places, including in the cards you sent back with bill payments (which bore the infamous exhortation, "Do not fold, spindle, or mutilate").
While punchcards are most associated with the "big-iron" mainframe computers of the 1950s through 1970s, they have a 200-year history of use for many applications, from the Jacquard Loom of 1801 to the "hanging chads" of the 2000 US presidential election. In between they were proposed for use in Babbage's never-finished Analytic Engine and used by Hollerith for data-tabulation for the 1890 US Census.
It should be possible to read most standard punch cards with a sheet-fed scanner (simplex is sufficient) and a simple black/white sensing program. DataMuseum.dk has such a program, aptly named "florida2k" written in python3.
- Aperture card
- Hollerith card
- IBM card (original 80-column version)
- Jacquard Loom
- Korsakov card
- Mark Sense card
- UNIVAC 90-column card
- Votomatic card (used in election ballots)
- The Douglas W. Jones Punched Card Page
- The Punched Card: shows details of a number of card formats and character encoding schemes
- Google60: Cute web app showing how Google's interface might have been in the 1960s, complete with simulated keypunch
- The little secret that haunts corporate America ... A technology that won't go away.
- If all digital data were stored on punch cards, how big would Google's data warehouse be?