Punch card
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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. There is a widespread
myth that it was designed to fit in the currency trays used for that era's
larger dollar bills, but recent investigations have refuted that. 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 format, which had used 90 columns of
round holes.
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.
Some of the above material is based on FOLDOC.
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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)
o Dave(Column 1,Row 1)
o Michael(Column 1,Row 2 )
o Mark(Column 1,Row 3)
o 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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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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