A hole is a yes or a no
The idea behind punched media is simple. At a given spot on a card or strip, there is either a hole or there is not. That is one piece of information, and a pattern of such spots can stand for a letter, a digit or an instruction. The same principle underlies binary numbers, even though punched media often predated electronic computers and were not designed with them in mind.
From looms to tabulators
The best-known early use of punched cards was in weaving. In the early 1800s, Joseph Marie Jacquard’s loom used chains of punched cards to select which threads were lifted for each pass of the shuttle. The cards were, in effect, a stored pattern that a machine could follow without a skilled worker choosing every thread. Charles Babbage later planned to use similar cards for his Analytical Engine, an idea that makes the loom a frequent stop in stories about the roots of programming.
Cards entered data processing in the late 1800s. Herman Hollerith developed electromechanical tabulating machines for the United States census of 1890, in which each person’s record was a card with holes in set positions. Pins passed through the holes to complete electrical circuits, and counters advanced accordingly. The company Hollerith founded was one of several that later merged into what became IBM, and card equipment remained a large business through much of the twentieth century.
The standard card
By the late 1920s, IBM had settled on a card with 80 columns, each column able to hold one character. A letter or digit was represented by one or more holes in a column, and the card was printed along the top so that a person could read what had been punched. Companies built whole workflows around these cards: keypunch operators typed records, sorters arranged them, and tabulators produced totals.
When electronic computers arrived, cards were the obvious way to feed them. A programmer wrote code on paper, a keypunch operator turned it into a deck, and the deck was handed in at a computing center window. Results came back later, often hours or a day. A typo meant finding the faulty card, punching a replacement and resubmitting the deck. Many programmers marked the top edge of a deck with a diagonal stripe so that a dropped stack could be put back in order.
What cards were good and bad at
Cards had real strengths:
- Each card was a separate record, so a deck could be sorted, shuffled or edited by hand.
- A card could be read by a person as well as a machine.
- They were cheap and easy to produce with simple equipment.
They also had clear limits. A card held only 80 characters, so a large dataset meant a very large stack of cardboard. Decks were heavy and took up cabinet space. They were vulnerable to moisture, folding and mishandling, and a deck in the wrong order was effectively a different program. Storing and shipping cards was a real logistics task in organizations with large files.
Paper tape
Paper tape followed a different path. Long strips with rows of holes were used with telegraph and teleprinter systems well before computers, since a message could be punched at one place and sent later or at a steady speed. Early telegraph codes used five holes across the tape, while later codes used more positions per row, which allowed larger character sets such as the ones discussed under character encoding.
Computers adopted tape as well. It was compact compared with a deck of cards, and a program or a data set formed one continuous roll. It was convenient for small machines, particularly minicomputers and some laboratory systems of the 1960s and 1970s, where a tape reader and punch were common attachments. Operators could load a short bootstrap program from tape and then use it to read in larger ones.
The weaknesses were different from those of cards. Editing a tape meant cutting and splicing, or punching a new one. Tape could tear, and it was easy to lose your place. Programmers still made use of it because it was inexpensive and the equipment was widely available.
Other uses
Punched media were not only for programs. Cards were used for election ballots in some places, for utility bills that customers returned with payment, and for library checkouts. Many organizations kept archives of their records as cards for years. Early data processing departments often had rooms filled with card files, and the phrase “do not fold, spindle or mutilate” became a recognizable warning on cards that were meant to be machine-read.
Why they faded
Magnetic tape and disks gradually took over storage because they were denser and faster, and because the data could be rewritten. Cards lingered longest as an input method, since terminals and interactive computing took time to spread. During the 1970s and 1980s, keyboards connected directly to computers replaced the keypunch in most places, and cards disappeared from everyday work. Paper tape had a similar decline as cheaper magnetic media arrived for small systems.
Legacy
Traces of the punched card remain. Some programming conventions, such as the 80-character line width that influenced early terminals and text files, are often linked to the standard card, though the exact chain of influence varies from case to case. Punched media also remain a practical concern for archivists: boxes of cards and reels of tape in libraries and museums can still be read, but only with some care, and the effort of preserving old computers includes the readers that understand them.
Punched media show that data storage does not need to be electronic or even magnetic to be useful. They were slow and bulky, but for a long time they were the practical way to move information into and out of machines.