Herman Hollerith
Copyright (c) 1997. Maxfield
& Montrose Interactive Inc
Hollerith's Punched Cards |
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| The first practical use of punched cards for data processing is credited to the American inventor Herman Hollerith, who decided to use Jacquard's punched cards to represent the data gathered for the American census of 1890, and to read and collate this data using an automatic machine. |
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| Many references state that Hollerith originally made his punched cards the same size as the dollar bills of that era, because he realized that it would be convenient and economical to buy existing office furniture, such as desks and cabinets, that already contained receptacles to accommodate stacks of bills. Other sources consider this to be a popular fiction. Whatever the case, we do know that these cards were eventually standardized at 7 and 3/8 inches by 3 and 1/4 inches, and Hollerith's many patents permitted his company (which became International Business Machines (IBM) in 1924) to hold an effective monopoly on punched cards for many years. |
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| Hollerith, who was no one's fool, had quickly realized that the real money was not to be made in the tabulating machines themselves, but rather in the tens or hundreds of thousands of cards that were used to store data. Although other companies came up with innovative ways to bypass Hollerith's patents, they failed to capitalize on their advances, thereby giving IBM a chance to regain the high ground. |
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| For example, Hollerith's early cards were punched with round
holes, because his prototype machine employed cards with holes created using a tram
conductor's ticket punch. Hollerith continued to use round holes in his production machines, which effectively limited the amount of data that could be stored on each card. By the early 1900s, Hollerith's cards supported 45 columns, where each column could be used to represent a single character or data value. |
This set the standard until 1924-1925, when the Remington Rand Corporation evolved a technique for doubling the amount of information that could be stored on each card. But they failed to exploit this advantage to its fullest extent, and, in 1929-1931, IBM responded by using rectangular holes, which allowed them to pack 80 columns of data onto each card. Although other formats appeared sporadically (including some from IBM), the 80 column card shown above overwhelmingly dominated the punched card market from around the 1950s onward. | |
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IBM 80-column punched card format |
The figure to the left shows one of the early 80 column IBM cards (not to scale). Each card contains 12 rows of 80 columns, and each column is typically used to represent a single piece of data such as a character. The top row is called the "12" or "Y" row; the second row from the top is called the "11" or "X" row; and the remaining rows are called the "0" to "9" rows (indicated by the numbers printed on the cards). | |
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| This figure (which took one heck of a long time to draw let me tell you) illustrates one of the early, simpler coding schemes, in which each character could be represented using no more than three holes. (Note that we haven't shown all of the different characters that could be represented). Over the course of time, more sophisticated coding schemes were employed to allow these cards to represent different character sets such as ASCII and EBCDIC; the rows and columns stayed the same, but different combinations of holes were used. |
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| One advantage of punched cards over paper tapes was that the textual equivalent of the patterns of holes could be printed along the top of the card (one character above each column). Another advantage was that it was easy to replace any cards containing errors. However, the major disadvantage of working off-line (with both punched cards and paper tapes) was that the turn-around time to actually locate and correct any errors was horrendous. | Although punched cards are rarely used now, we endure their legacies to this day. For example, the first computer monitors were constructed so as to display 80 characters across the screen. This number was chosen on the basis that you certainly wouldn't want to display fewer characters than were on an IBM punched card, and there didn't appear to be any obvious advantage to being able to display more characters than were on a card (see also John Vincent Atanasoff's burnt offerings). |
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| These notes are abstracted from the book Bebop BYTES Back (An Unconventional Guide to Computers) Copyright Information |
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