Punch cards, developed by Herman Hollerith of Buffalo, New York, to tabulate the 1890 U.S. Census, played a major role in the development of computer technology and the growth of its role in society.  They were the principal means of inputting data into a computer in the days of the large mainframe (1950s and 1960s) when I first began to use these machines as an undergraduate at MIT.

Punching a set of these cards (properly known as Hollerith cards, but more commonly called IBM cards) was how one prepared data for computer analysis.  It was a tedious and time-consuming activity.  After the cards were punched (one by one on a card punch machine), you stood in line to deliver your deck to the computation center where it would be run as part of a batch.  You returned several hours later (or often the next morning) and stood in line again to pick up the cards and the printout reporting the results of the run, which, as often as not, was gibberish, because one or more of the cards was punched incorrectly.

In fact, punch cards were used extensively before computers were developed.  Tabulators and counter-sorters performed statistical operations with them beginning in the 1890s and on into the first half of the 20th century.  Hollerith founded the Tabulating Machine Company in 1896.  The firm was the forerunner of the Computer Tabulating Recording Company, which changed its name to International Business Machines--IBM.

Links:
= highly recommended

Hollerith's Punched Cards, from Bebop Bytes Back:  An Unconventional Guide to Computers, by Clive "Max" Maxfield and Alvin Brown.  A nice, breezy history and discussion of the punch card.

Hollerith Manual Card Punch (1930s) and IBM card punches, card verifiers, and counter-sorters (1950s and 1960s) from the collection of The Computer Museum of America in San Diego, CA. Photo and discussion of this device from the 1930s.

Punch Card Gallery, a section of John Walker's Univac Memories.  Nostalgia for old computers from the founder of AutoDesk, Inc., on the Fourmilab Switzerland site.

Anatomy of a Hollerith Card.  More nostalgia; this from David L. Mills at the University of Delaware.

Profile of Herman Hollerith from the National Inventors Hall of Fame.  Hollerith was inducted in 1990.

Herman Hollerith, a detailed biography by J. J. O'Connor and E. F. Robertson at the School of Mathematics and Statistics, University of St. Andrews, Scotland.

Herman Hollerith, the World's First Statistical Engineer, by Mark Russo of the University of Rochester (NY) Department of History.  A very detailed biography, explaining how and why Hollerith invented the punch card and how it was used.

Do not fold, spindle or mutilate:  A cultural history of the punch card, by Stephen Lubar, historian of technology at the Smithsonian Institution, May 1991.  Interesting study of the punch card as a cultural object.

19th Century Contributions and their Impact on Elements of Modern Computers, by Paul E. Dunne, Department of Computer Science, University of Liverpool (UK). 

IBM Cards.  $2.35/100 in 5 mil thickness, $4.05 for 7 mil, and $5.25 for 10 mil.  From CFS Binding Supplies. Why is a binding supply company selling IBM cards?  And why are they smaller than the standard 7 3/8 by 3 1/4? And who buys them, anyway?

IBM Punch Card Systems in the U.S. Army, by Charles M. Province, founder and president of The Patton Society.  An unusual look at the use of punch cards in the U.S. Army and their relationship to General George S. Patton.  Many interesting old photos, including one of the punch card recording Patton's death.