Punched Cards
Punched cards were rectangular pieces of thin cardboard, historically used as the primary medium for inputting and storing data and instructions in early computers and data processing machines. Data was represented by patterns of holes, where the presence or absence of a hole in a specific position on the card determined a character or command. These cards were read by machines that detected the holes and converted them into digital information for the computer.
Components and Function
Material: Stiff, thin cardboard stock.
Data Representation: The card's surface was divided into columns, and rows of positions within these columns. Holes punched in these positions represented data.
Encoding: A system of "zone" and "digit" punches allowed a single column to represent different characters, often using a combination of punches in the numeric (0-9) and zone (11, 12, 0) rows.
Chads: The small pieces of paper punched out of the card were known as "chads" or "pieces of chad".
How They Were Used
Input: A human operator or machine used a keypunch machine to punch holes into the card, creating the desired pattern for a specific data item or program instruction.
Reading: The stack of punched cards was then fed into a card reader, which used various methods, including light sensors, to detect the holes.
Conversion: The detected holes were converted into electrical impulses, which the computer then processed as digital information.
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