Who introduced punched cards?

The correct answer is Herman Hollerith.

Herman Hollerith introduced the punched cards. It was first used for vital statistics tabulation by the New York City Board of Health and several other states. Hollerith invented and used the punched cards to help analyze the 1890 US census data. He used electricity to read, count and sort punched cards whose holes represented data gathered by census takers.

Basically, a punched card is a piece of paper that mainly contains digital information represented by the presence or the absence of holes in predefined positions.
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