Punch card

The punch card (or "Hollerith" card) is a medium for holding information for use by automated 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 during the 1960s and 1970s, punch cards were a primary medium for data storage and processing, but are now long obsolete outside of a few legacy systems.

The punched card actually predates computers considerably, originating in 1801 as a control device for Jacquard looms. Such cards were also used as an input method for the primitive calculating machines of the late 19th century.

The version by Herman Hollerith, patented on June 8, 1887 and used with mechanical tabulating machines in the 1890 U.S. Census, was a piece of cardboard about 90 mm by 215 mm, with round holes. The early applications of punched cards all used specifically-designed card layouts. It wasn't until around 1928 that punched cards and machines were made "general purpose". In that year, punched was were made a standard size, corresponding to the US currency of the day.

To compensate for the cyclical nature of the Census Bureau's demand for his machines, Hollerith founded the Tabulating Machine Company (1896) a predecessor to IBM. IBM manufactured a wide variety of business machines and eventually married the punched card to its early computers, encoding binary information as patterns of small rectangular holes. That IBM format eventually won out over the Univac 90-character format, which used 45 columns (2 characters in each) of 12 round holes.

Punched (Hollerith) cards are made of smooth stock, .007 of an inch thick. There are about 143 cards to the inch.

The method is quite simple: On a piece of light-weight cardboard, successive positions either have a hole punched through them or are left intact. The rectangular bits of paper punched out are called chads. Thus, each punch location on the card represents a single binary digit (or "bit"). Each column on the card contained several punch positions (multiple bits), thereby allowing one column of the card to represent a digit or other character. Cards could be made in which every possible punch position had a hole: These were called "lace cards." The IBM card format, which became standard, held 80 columns of 12 punch locations each, representing 80 characters (since 12 bits is more than enough for representing a character, not all combinations were used.) originally coded: 1 punch (digit[0-9]) was a digit, 2 punches (zone[12,11,0] + digit[1-9]) was a letter, 3 punches (zone[12,11,0] + digit[1-7] + 8) was a special character, later the introduction of EBCDIC allowed columns with as many as 6 punches (zones[12,11,0,8,9] + digit[1-7]). Other coding schemes, sizes of card, and hole shapes were tried at various times.

Often the text was also printed at the top of the card, allowing humans to read the text as well, if the cards were produced by a card-punch machine (called a "key-punch"), which was like a large, very noisy typewriter. There were also cards with all the punch positions perforated so programming or data could be punched out manually, one hole at a time, with a device like a blunt pin with its wire bent into a finger-ring on the other end.

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 feed hundreds of cards through in a very short time.

One of the key advantages of this system is that a computer was not required to encode information onto the cards -- the typewriter-like card-punch machine was all that was needed -- and "key-punch operators" (who did nothing but punch cards full-time on such machines) were in great demand. (Quality control was often having two different operators key the same data, with the 2nd using a card-verifier instead of a card-punch. If a card failed verification, the card-verifier would stop, letting the operator replace the card with a corrected one.) When the time came to transfer the information thus encoded into the computer, the process could occur at very high speed (either by the computer itself or by a separate device that "read" the cards and "wrote" the data onto magnetic tapes (or, later, on removable hard disks) that could then be mounted on the computer), thus making best use of expensive computer time.

Punched-card systems fell out of favor in the 1970s, as disk and tape storage became cost effective, and interactive terminals meant that users could edit their work with the computer directly rather than requiring the intermediate step of the punched cards.

However, their influence lives on through many standard conventions and file formats. The terminals that replaced the punched cards displayed 80 columns of text, for compatibility with existing software. Many programs still operate on the convention of 80 text columns, although strict adherence to that is fading as newer systems employ graphical user interfaces with variable-width type fonts.

See also: History of computing hardware, computer storage, memory, Hollerith

Some of the above material is based on FOLDOC.


duplicate article from "Hollerith" Hollerith cards were the punch cards used to store/read information that was acted on by Hollerith machines. They were pioneered by Herman Hollerith for use in the 1890 census of the United States, and the rights to the patents on this technology was bought by Thomas J. Watson SR., founder of IBM in 1914. He then went on to license use of this technology to governments and corporations all over the western world prior to World War II. The cards were punched manually, in a row/column format, where each column presented a question, and corresponding row entries for that column held the various answers that were possible, for example:

  • What is your name?(Column 1)
    • Dave(Column 1,Row 1)
    • Michael(Column 1,Row 2 )
    • Mark(Column 1,Row 3)
    • Paul(Column 1,Row 4)

There was approx. 8 columns, and 20 rows, though it varied on the machine being used. The questions were normally asked in questionnaire style, and this allowed for great variation in answers. The cards were used to track resources such as railways, goods, people and even slave labor in the third reich.

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Duplicate article from "Hollerith card"

The Hollerith card is a punch card used in data processing prior to the advent of effective, practical magnetic storage systems. The cards could contain up to 80 characters, made up of numbers, capital letters, and a few symbols. Up to three punches per column were made, and the encoded data was often printed in typewritten letters along the top.

Variations included preprinted areas for marking new information with pen and ink, which was then encoded by a keypunch operator and checked by a verifier.

Electromechanical equipment for punching, sorting and printing the cards was manufactured. Later, this was done with computers.

A group of such cards is called a deck.

For a time, magnetically encoded cards were used that had the same shape and size. The magnetic encoding achieved much higher density and could hold more information.

The Hollerith card was adapted by Herman Hollerith, from a card used by Joseph Jacquard for controlling his mechanical weaving loom. It first use was in analysing the results of the US Census. Hollerith made the card the same size as the dollar bill of the time, so that storage cabinets designed for money could be used for his cards.


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