A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contained either commands for controlling automated machinery or data for data processing applications. Both commands and data were represented by the presence or absence of holes in predefined positions.
Now obsolete as a recording medium, punched cards were widely used throughout the 20th century for controlling textile looms and in the late 19th and early 20th century for controlling fairground organs and related instruments. Punched cards were used through most of the 20th century in what became known as the data processing industry; the use of unit record machines, organized into data processing systems, for data input, processing, and storage. Early digital computers used punched cards, often prepared using keypunch machines, as the primary medium for input of both computer programs and data.
- 1 History
- 2 Nomenclature
- 3 Card formats
- 4 IBM punched card manufacturing
- 5 Cultural impact
- 6 Standards
- 7 Card handling equipment
- 8 See also
- 9 References
- 10 Further reading
- 11 External links
Punched cards were first used around 1725 by Basile Bouchon and Jean-Baptiste Falcon as a more robust form of the perforated paper rolls then in use for controlling textile looms in France. This technique was greatly improved by Joseph Marie Jacquard in his Jacquard loom in 1801.
Semen Korsakov was reputedly the first to use the punched cards in informatics for information store and search. Korsakov announced his new method and machines in September 1832; rather than seeking patents, he offered the machines for public use.
Charles Babbage proposed the use of "Number Cards", "pierced with certain holes and stand opposite levers connected with a set of figure wheels ... advanced they push in those levers opposite to which there are no holes on the card and thus transfer that number" in his description of the Calculating Engine's Store.
Herman Hollerith invented the recording of data on a medium that could then be read by a machine. Prior uses of machine readable media, such as those above (other than Korsakov), had been for control, not data. "After some initial trials with paper tape, he settled on punched cards...", developing punched card data processing technology for the 1890 US census.
Hollerith founded the Tabulating Machine Company (1896) which was one of four companies that merged to form Computing Tabulating Recording Company (CTR), later renamed the International Business Machines Corporation (IBM). IBM manufactured and marketed a variety of unit record machines for creating, sorting, and tabulating punched cards, even after expanding into electronic computers in the late 1950s. IBM developed punched card technology into a powerful tool for business data-processing and produced an extensive line of general purpose unit record machines. By 1950, the IBM card and IBM unit record machines had become ubiquitous in industry and government. "Do not fold, spindle or mutilate," a generalized version of the warning that appeared on some punched cards (generally on those distributed as paper documents to be later returned for further machine processing, checks for example), became a motto for the post-World War II era. 
From the 1900s, into the 1950s, punched cards were the primary medium for data entry, data storage, and processing in institutional computing. According to the IBM Archives: "By 1937... IBM had 32 presses at work in Endicott, N.Y., printing, cutting and stacking five to 10 million punched cards every day." Punched cards were even used as legal documents, such as U.S. Government checks and savings bonds. The UNITYPER introduced magnetic tape for data entry in the 1950s. During the 1960s, the punched card was gradually replaced as the primary means for data storage by magnetic tape, as better, more capable computers became available. Mohawk Data Sciences introduced a magnetic tape encoder in 1965, a system marketed as a keypunch replacement which was somewhat successful, but punched cards were still commonly used for data entry and programming until the mid-1980s when the combination of lower cost magnetic disk storage, and affordable interactive terminals on less expensive minicomputers made punched cards obsolete for this role as well. However, their influence lives on through many standard conventions and file formats. The terminals that replaced the punched cards, the IBM 3270 for example, displayed 80 columns of text in text mode, for compatibility with existing software. Some programs still operate on the convention of 80 text columns, although fewer and fewer do as newer systems employ graphical user interfaces with variable-width type fonts.
Today punched cards are mostly obsolete and replaced with other storage methods, except for a few legacy systems and specialized applications.
The terms punched card, punch card, and punchcard were all commonly used, as were IBM card and Hollerith card (after Herman Hollerith). IBM used "IBM card" or, later, "punched card" at first mention in its documentation and thereafter simply "card" or "cards". The term punched card was generally avoided for blank cards, with other terms such as tabulating card, or tab card used. Specific formats were often indicated by the number of character positions available, e.g. 80-column card. A sequence of cards that was input to or output from some step in an application's processing was called a card deck or simply deck. The rectangular, round, or oval bits of paper punched out were called chad (chads) or chips (in IBM usage). Multi-character data, such as a name, line of an address, or multi-digit number, was stored in adjacent card columns known as a field.
The first application of Hollerith's punched cards, the 1890 US census, used blank cards. Following that cards commonly had printing such that the row and column position of a hole could be identified. For some applications printing might have included fields, named and marked by vertical lines, logos, and more. "General purpose" layouts (see, for example, the IBM 5081 below) were also available. Some cards had one upper corner cut so that cards not oriented correctly, or cards with different corner cuts, could be easily identified.
Hollerith's punched card formats
Herman Hollerith was awarded a series of patents in 1889 for mechanical tabulating machines. These patents described both paper tape and rectangular cards as possible recording media. The card shown in U.S. Patent 395,781 of June 8 was preprinted with a template and had hole positions arranged close to the edges so they could be reached by a railroad conductor's ticket punch, with the center reserved for written descriptions. Hollerith was originally inspired by railroad tickets that let the conductor encode a rough description of the passenger:
- "I was traveling in the West and I had a ticket with what I think was called a punch photograph...the conductor...punched out a description of the individual, as light hair, dark eyes, large nose, etc. So you see, I only made a punch photograph of each person."
Use of the ticket punch proved tiring and error prone, so Hollerith invented a pantograph "keyboard punch" that allowed the entire card area to be used. It also eliminated the need for a printed template on each card, instead a master template was used at the punch; a printed reading board could be placed under a card that was to be read manually. Hollerith envisioned a number of card sizes. In an article he wrote describing his proposed system for tabulating the 1890 U.S. Census, Hollerith suggested a card 3 inches by 5½ inches of Manila stock "would be sufficient to answer all ordinary purposes."
The cards used in the 1890 census had round holes, 12 rows and 24 columns. A reading board for these cards can be seen at the Columbia University Computing History site. At some point, 3 1⁄4 by 7 3⁄8 inches (82.550 by 187.325 mm) became the standard card size, a bit larger than the United States one-dollar bill (silver certificates) at the time, because some existing storage and feeding devices could be adapted. The dollar bill was reduced to its current size in 1929. The Columbia site also says Hollerith took advantage of available boxes designed to transport paper currency.
Hollerith's original system used an ad-hoc coding system for each application, with groups of holes assigned specific meanings, e.g. sex or marital status. His tabulating machine had up to 40 counters, each with a dial divided into 100 divisions, with two indicator hands; one which stepped one unit with each counting pulse, the other which advanced one unit every time the other dial made a complete revolution. This arrangement allowed a count up to 10,000. During a given tabulating run, each counter was typically assigned a specific hole. Hollerith also used relay logic to allow counts of combination of holes, e.g. to count married females.
Later designs standardized the coding. These cards had ten rows, each row assigned a digit value, 0 through 9, and 45 columns. This provided for a field (adjacent columns) to represent multi-digit numbers that tabulators could sum, instead of their simply counting cards. Hollerith's 45 column punched cards are illustrated in Comrie's The application of the Hollerith Tabulating Machine to Brown's Tables of the Moon.
IBM 80-column punched card formats and character codes
This IBM card format, designed in 1928, had rectangular holes, 80 columns with 12 punch locations each, one character to each column. Card size was exactly 7 3⁄8 by 3 1⁄4 inches (187.325 mm × 82.55 mm). The cards were made of smooth stock, 0.007 inches (180 µm) thick. There are about 143 cards to the inch (56/cm). In 1964, IBM changed from square to round corners. They came typically in boxes of 2000 cards or as continuous form cards. Continuous form cards could be both pre-numbered and pre-punched for document control (checks, for example).
The lower ten positions represented (from top to bottom) the digits 0 through 9. The top two positions of a column were called zone punches, 12 (top) and 11. Originally only numeric information was punched, with 1 punch per column indicating the digit. Signs could be added to a field by overpunching the least significant digit with a zone punch: 12 for plus and 11 for minus. Zone punches had other uses in processing as well, such as indicating a master record.
______________________________________________ /&-0123456789ABCDEFGHIJKLMNOPQR/STUVWXYZ Y / x xxxxxxxxx X| x xxxxxxxxx 0| x xxxxxxxxx 1| x x x x 2| x x x x 3| x x x x 4| x x x x 5| x x x x 6| x x x x 7| x x x x 8| x x x x 9| x x x x |________________________________________________
Reference: Note: The X and Y zones were also called the 11 and 12 zones, respectively.
In 1931 IBM began introducing multiple punches for upper-case letters and special characters. A letter had two punches (zone [12,11,0] + digit [1–9]); most special characters had two or three punches (zone [12,11,0,or none] + digit [2–7] + 8); a few special characters were exceptions (in EBCDIC "&" was 12 only, "-" was 11 only, and "/" was 0 + 1). With these changes, the information represented in a column by a combination of zones [12, 11] and digits [1–9] was dependent on the use of that column. For example the combination "12-1" was the letter "A" in an alphabetic column, a plus signed digit "1" in a signed numeric column, or an unsigned digit "1" in a column where the "12" had some other use. The introduction of EBCDIC in 1964 allowed columns with as many as six punches (zones [12,11,0,8,9] + digit [1–7]). IBM and other manufacturers used many different 80-column card character encodings. A 1969 American National Standard defined the punches for 128 characters and was named the Hollerith Punched Card Code (often referred to simply as Hollerith Card Code), honoring Hollerith.
For some computer applications, binary formats were used, where each hole represented a single binary digit (or "bit"), every column (or row) was treated as a simple bitfield, and every combination of holes was permitted. For example, the IBM 711 card reader used with the 704/709/7090/7094 series scientific computers treated every row as two 36-bit words, ignoring 8 columns. (The specific 72 columns used were selectable using a plugboard control panel, which was almost always wired to select columns 1–72.) Sometimes the ignored columns (usually 73–80) were used to contain a sequence number for each card, so the card deck could be sorted to the correct order in case it was dropped. Other computers, such as the IBM 1130 or System/360, used every column. An alternative format, used by the IBM 704's IBM 714 native card reader, was referred to as Column Binary or Chinese Binary, and used 3 columns for each 36-bit word. The IBM 1402 could also be used in Column Binary mode, which stored two characters in every column, or one 36-bit word in three columns when used as input device for other computers. However, most of the older card punches were not intended to punch more than 3 holes in a column, so they could not be used to produce binary cards.
As a prank, in binary mode, cards could be punched where every possible punch position had a hole. Such "lace cards" lacked structural strength, and would frequently buckle and jam inside the machine.
The 80-column card format dominated the industry, becoming known as just IBM cards, even though other companies made cards and equipment to process them.
One of the most common printed punched cards was the IBM 5081 card format, a general purpose layout with no field divisions. This format had digits printed on it corresponding to the punch positions of the digits in each of the 80 columns. Other card vendors manufactured cards with this same layout and number.
Mark sense cards
- Mark sense (Electrographic) cards, developed by Reynold B. Johnson at IBM, had printed ovals that could be marked with a special electrographic pencil. Cards would typically be punched with some initial information, such as the name and location of an inventory item. Information to be added, such as quantity of the item on hand, would be marked in the ovals. Card punches with an option to detect mark sense cards could then punch the corresponding information into the card.
- Aperture cards have a cut-out hole on the right side of the punched card. A 35 mm microfilm chip containing a microform image is mounted in the hole. Aperture cards are used for engineering drawings from all engineering disciplines. Information about the drawing, for example the drawing number, is typically punched and printed on the remainder of the card. Aperture cards have some advantages over fully digital systems for archival purposes.
IBM Stub cards or Short cards
The 80-column card could be scored, on either end, creating a stub that could be torn off, leaving a stub card or short card. A common length for stub cards was 51-columns. Stub cards were used in applications requiring tags, labels, or carbon copies.
According to the IBM Archive: IBM's Supplies Division introduced the Port-A-Punch in 1958 as a fast, accurate means of manually punching holes in specially scored IBM punched cards. Designed to fit in the pocket, Port-A-Punch made it possible to create punched card documents anywhere. The product was intended for "on-the-spot" recording operations—such as physical inventories, job tickets and statistical surveys—because it eliminated the need for preliminary writing or typing of source documents..
IBM 96-column punched card format
In the early 1970s IBM introduced a new, smaller, round-hole, 96-column card format along with the IBM System/3 computer. These cards had tiny (1 mm), circular holes, smaller than those in paper tape. Data was stored in six-bit binary-coded decimal code, with three rows of 32 characters each, or 8-bit EBCDIC. In this format, each column of the top tiers are combined with two punch rows from the bottom tier to form an 8-bit byte, and the middle tier is combined with two more punch rows, so that each card contains 64 bytes of 8-bit-per-byte binary coded data.
Powers/Remington Rand UNIVAC card formats
The Powers/Remington Rand card format was initially the same as Hollerith's; 45 columns and round holes. In 1930, Remington Rand leap-frogged IBM's 80 column format from 1928 by coding two characters in each of the 45 columns – producing what is now commonly called the 90-column card. There are two sets of six rows across each card. The rows in each set are labeled 0, 1/2, 3/4, 5/6, 7/8 and 9. The even numbers in a pair are formed by combining that punch with a 9 punch. Alphabetic and special characters use 3 or more punches
IBM punched card manufacturing
IBM's Fred M. Carroll developed a series of rotary type presses that were used to produce the well-known standard tabulating cards, including a 1921 model that operated at 400 cards per minute (cpm). Later, he developed a completely different press capable of operating at speeds in excess of 800 cpm, and it was introduced in 1936. Carroll's high-speed press, containing a printing cylinder, revolutionized the manufacture of punched tabulating cards. It is estimated that between 1930 and 1950, the Carroll press accounted for as much as 25 percent of the company's profits
Discarded printing plates from these card presses, each printing plate the size of an IBM card and formed into a cylinder, often found use as desk pen/pencil holders, and even today are collectible IBM artifacts (every card layout had its own printing plate).
IBM initially required that its customers use only IBM manufactured cards with IBM machines, which were leased, not sold. IBM viewed its business as providing a service and that the cards were part of the machine. In 1932 the government took IBM to court on this issue. IBM fought all the way to the Supreme Court and lost in 1936; the court ruling that IBM could only set card specifications. In another case, heard in 1955, IBM signed a consent decree requiring, amongst other things, that IBM would by 1962 have no more than one-half of the punched card manufacturing capacity in the United States. Tom Watson Jr.'s decision to sign this decree, where IBM saw the punched card provisions as the most significant point, completed the transfer of power to him from Thomas Watson, Sr.
While punched cards have not been widely used for a generation, the impact was so great for most of the 20th century that they still appear from time to time in popular culture. For example:
- Artist and architect Maya Lin in 2004 designed a public art installation at Ohio University, titled "Input", that looks like a punched card from the air.
- Do Not Fold, Bend, Spindle or Mutilate: Computer Punch Card Art – a mail art exhibit by the Washington Pavilion in Sioux Falls, South Dakota.
- The Red McCombs School of Business at the University of Texas at Austin has artistic representations of punched cards decorating its exterior walls.
- At the University of Wisconsin - Madison, the exterior windows of the Engineering Research Building were modeled after a punched card layout, during its construction in 1966.
- At the University of North Dakota, the exterior of Gamble Hall, College of Business and Public Administration has a punch card spelling out "University of North Dakota." 
- In the Simpsons episode "Much Apu About Nothing", Apu showed Bart his Ph.D. thesis, the world's first computer tic-tac-toe game, stored in a box full of punched cards.
- In the Futurama episode "Mother's Day", as several robots are seen shouting 'Hey hey! Hey ho! 100110!' in protest, one of them burns a punch-card in a manner reminiscent of draft-card burning. In another episode, Put Your Head on My Shoulders, Bender offers a dating service. He hands characters punch-cards so they can put in what they want, before throwing them in his chest cabinet and 'calculating' the 'match' for the person. Bender is shown 'folding', 'bending', and 'mutilating' the card, accentuating the fact that he is making up the 'calculations'.
- In the 1964–65 Free Speech Movement, punched cards became a
metaphor... symbol of the "system"—first the registration system and then bureaucratic systems more generally ... a symbol of alienation ... Punched cards were the symbol of information machines, and so they became the symbolic point of attack. Punched cards, used for class registration, were first and foremost a symbol of uniformity. .... A student might feel "he is one of out of 27,500 IBM cards" ... The president of the Undergraduate Association criticized the University as "a machine ... IBM pattern of education."... Robert Blaumer explicated the symbolism: he referred to the "sense of impersonality... symbolized by the IBM technology."... ––Steven Lubar
- A legacy of the 80 column punched card format is that a display of 80 characters per row was a common choice in the design of character-based terminals. As of September 2014 some character interface defaults, such as the command prompt window's width in Microsoft Windows, remain set at 80 columns and some file formats, such as FITS, still use 80-character card images.
In Arthur C. Clarke's early short story Rescue Party, the alien explorers find a "... wonderful battery of almost human Hollerith analyzers and the five thousand million punched cards holding all that could be recorded on each man, woman and child on the planet". Writing in 1946, Clarke, like almost all sci-fi authors, had not then foreseen the development and eventual ubiquity of the computer.
- ANSI INCITS 21-1967 (R2002), Rectangular Holes in Twelve-Row Punched Cards (formerly ANSI X3.21-1967 (R1997)) Specifies the size and location of rectangular holes in twelve-row 3 1⁄4-inch-wide (83 mm) punched cards.
- ANSI X3.11 – 1990 American National Standard Specifications for General Purpose Paper Cards for Information Processing
- ANSI X3.26 – 1980/R1991) Hollerith Punched Card Code
- ISO 1681:1973 Information processing – Unpunched paper cards – Specification
- ISO 6586:1980 Data processing – Implementation of the ISO 7- bit and 8- bit coded character sets on punched cards. Defines ISO 7-bit and 8-bit character sets on punched cards as well as the representation of 7-bit and 8-bit combinations on 12-row punched cards. Derived from, and compatible with, the Hollerith Code, ensuring compatibility with existing punched card files.
Card handling equipment
Creation and processing of punched cards was handled by a variety of devices, including:
- Card image
- Computer programming in the punched card era
- History of computing hardware
- Kimball tag—punched card price tags
- Paper data storage
- Punched tape
- The initial version of this article, October 18, 2001, was based on material taken from the Free On-line Dictionary of Computing and incorporated under the "relicensing" terms of the GFDL, version 1.1.
- Cortada, James W. (1993) Before The Computer: IBM, NCR, Burroughs, & Remington Rand & The Industry They Created, 1865 - 1965, Princeton
- "Nightly News Aired on December 27, 2012 - Punch card voting lingers". Video.msnbc.msn.com. Retrieved 2013-10-05.
- Semen Korsakov's inventions, Cybernetics Dept. of MEPhI (Russian)
- Trogemann, Georg (eds.) et al. (2001). Computing in Russia. Verlag. pp. 47–49. The article is by Gellius N. Povarov, titled Semen Nikolayevich Korsakov- Machines for the Comparison of Philosophical Ideas
- Babbage, Charles (26 Dec 1837). On the Mathematical Powers of the Calculating Engine.
- "Columbia University Computing History – Herman Hollerith". Columbia.edu. Retrieved 2013-10-05.
- "History of the punch card". Whatis.techtarget.com. Retrieved 2013-10-05.
- "IBM Archive: Endicott card manufacturing". 03.ibm.com. Retrieved 2013-10-05.
- Lubar, Steven (1993). InfoCulture: The Smithsonian Book of Information Age Inventions. Houghton Mifflin. p. 302. ISBN 0-395-57042-5.
- Aspray (ed.), W. (1990). Computing before Computers. Iowa State University Press. p. 151. ISBN 0-8138-0047-1.
- "An important function in IBM Accounting is the automatic preparation of IBM cards." IBM 519 Principles of Operation, Form 22-3292-5, 1946
- "The IBM 1402 Card Read-Punch provides the system with simultaneous punched-card input and output. This unit has two card feeds." Reference Manual 1401 Data Processing System, Form A24-1403-4, 1961
- "IBM Archives: Fred M. Carroll". 03.ibm.com. Retrieved 2013-10-05.
- Truedsell, Leon E. (1965). The Development of Punch Card Tabulation in the Bureau of the Census 1890-1940. US GPO.
- IBM (1956). The Design of IBM Cards (PDF). 22-5526-4.
- "Railroad Gazette, April 19, 1895". Memory.loc.gov. Retrieved 2013-10-05.
- U.S. Patent 395,781, U.S. Patent 395,782, U.S. Patent 395,783
- [-245-] An Electric Tabulating System, The Quarterly, Columbia University School of Mines, Vol.X No.16 (April 1889)
- "Columbia University Computing History: Hollerith 1890 Census Tabulator". Columbia.edu. Retrieved 2013-10-05.
- Stanford Historic Displays at http://infolab.stanford.edu/pub/voy/museum/pictures/display/2-2-ElecKeyPunch.htm
- Bashe, Charles J.; Johnson, Lyle R.; Palmer, John H.; Pugh, Emerson W. (1986). IBM's Early Computers. Cambridge, Massachusetts: The MIT Press. p. 5. ISBN 0-262-02225-7. Also see pages 5-14 for additional information on punched cards.
- Plates from: Comrie, L.J. (1932). "The application of the Hollerith Tabulating Machine to Brown's Tables of the Moon". Monthly Notices of the Royal Astronomical Society 92 (7): 694–707. Bibcode:1932MNRAS..92..694C. doi:10.1093/mnras/92.7.694.
- Comrie, L.J. (1932). "The application of the Hollerith tabulating machine to Brown's tables of the moon". Monthly Notices of the Royal Astronomical Society 92 (7): 694–707. Bibcode:1932MNRAS..92..694C. Retrieved 2009-04-17.
- IBM Archive: 1928.
- IBM Archive: Old/New-Cards.
- p. 405, "How Computational Chemistry Became Important in the Pharmaceutical Industry", Donald B. Boyd, chapter 7 in Reviews in Computational Chemistry, Volume 23, edited by Kenny B. Lipkowitz, Thomas R. Cundari and Donald B. Boyd, Wiley, 2007, ISBN 978-0-470-08201-0.
- IBM (1953). Principles of IBM Accounting. 224-5527-2.
- "Punched Card Codes". Cs.uiowa.edu. Retrieved 2013-10-05.
- Pugh, Emerson W. (1995). Building IBM: Shaping and Industry and Its Technology. MIT Press. pp. 50–51. ISBN 978-0-262-16147-3.
- Special characters are non-alphabetic, non-numeric, such as "&#,$.-/@%*?"
- Winter, Dik T. "80-column Punched Card Codes". Archived from the original on April 8, 2007. Retrieved November 6, 2012.
- Jones, Douglas W. "Punched Card Codes". Retrieved February 20, 2007.
- Mackenzie, C.E. (1980). Coded Character Sets, History and Development, Addison-Wesley, page 7
- Thelen, Ed. "Chinese Binary". Retrieved 12 December 2013.
- LoTurco, Ed (January 2004). "The Engineering Aperture Card: Still Active, Still Vital" (PDF). EDM Consultants. Archived from the original (PDF) on November 28, 2007. Retrieved October 10, 2007.
- "IBM Archive: Port-A-Punch". 03.ibm.com. Retrieved 2013-10-05.
- Winter, Dik T. "96-column Punched Card Code". Archived from the original on April 15, 2007. Retrieved November 6, 2012.
- Aspray (ed.). op. cit. p. 142.
- "The Punched Card". Quadibloc.com. Retrieved 2013-10-05.
- Winter, Dik T. "90-column Punched Card Code". Archived from the original on February 28, 2005. Retrieved November 6, 2012.
- "IBM Archives/Business Machines: Fred M. Carroll". 03.ibm.com. Retrieved 2013-10-05.
- "IBM Archives: (IBM) Carroll Press". 03.ibm.com. Retrieved 2013-10-05.
- Belden, Thomas; Belden, Marva (1962). The Lengthening Shadow: The Life of Thomas J. Watson. Little, Brown & Company.
- "IBM Archives:1939 Layout department". 03.ibm.com. Retrieved 2013-10-05.
- "International Business Machines Corp. v. United States, 298 U.S. 131 (1936)". Justia.
- Belden (1962) pp.300-301
- "Mayalin.com". Mayalin.com. 2009-01-08. Retrieved 2013-10-05.
- Washingtonpavilion.org[dead link]
- "University of Wisconsin-Madison Buildings:". Fpm.wisc.edu. Retrieved 2013-10-05.
- "business.und.ed". Business.und.edu. 2013-09-24. Retrieved 2013-10-05.
- "Photo of Gamble Hall by gatty790". Panoramio.com. Retrieved 2013-10-05.
- Lubar, Steven. "Do Not Fold, Spindle Or Mutilate: A Cultural History Of The Punch Card" (PDF). Journal of American Culture 1992 (Winter). Retrieved June 12, 2011.
- Fierheller, George A. (2006). Do not fold, spindle or mutilate: the "hole" story of punched cards (PDF). Stewart Pub. ISBN 1-894183-86-X. Retrieved March 30, 2011. An accessible book of recollections (sometimes with errors), with photographs and descriptions of many unit record machines.
- Murray, Francis J. (1961). Mathematical Machines Volume 1: Digital Computers. Columbia University Press. Includes a description of Samas punched cards and illustration of an Underwood Samas punched card.
|Wikimedia Commons has media related to Punch card.|
- IBM. "The IBM Punched Card". Retrieved April 25, 2014.
- Lubar, Steve (May 1991). "Do not fold, spindle or mutilate: A cultural history of the punch card". Archived from the original on 2006-08-30.
- Jones, Douglas W. "Punched Cards". Retrieved October 20, 2006. (Collection shows examples of left, right, and no corner cuts.)
- VintageTech – a U.S. company that converts punched cards to conventional media
- Dyson, George (March 1999). "The Undead". Wired magazine 7 (3). Retrieved October 2006. article about modern-day use of punched cards
- Williams, Robert V. (2002). "Punched Cards: A Brief Tutorial". IEEE Annals – Web extra. Retrieved 2015-03-26.
- UNIVAC Punch Card Gallery (Shows examples of both left and right corner cuts.)
- Cardamation at the Wayback Machine (archived October 17, 2011) – a U.S. company that supplied punched card equipment and supplies until 2011.
- An Emulator for Punched cards
- Brian De Palma (Director) (1961). 660124: The Story of an IBM Card (Film).
- Povarov G.N. Semen Nikolayevich Korsakov. Machines for the Comparison of Philosophical Ideas. In: Trogemann, Georg; Ernst, Wolfgang and Nitussov, Alexander, Computing in Russia: The History of Computer Devices and Information Technology Revealed (pp 47–49), Verlag, 2001. Translated by Alexander Y. Nitussov. ISBN 3-528-05757-2, ISBN 978-3-528-05757-2
- Korsakov S.N. A Depiction of a New Research Method, Using Machines which Compare Ideas, Ed. by Alexander Mikhailov, MEPhI, 2009 (Russian)