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An icon of early computing, the punched card was very low density but robust — and could be altered and read by unaided, skilled humans at a pinch.
Ultimately deriving from automated weaving machines of the mid-18th century, IBM was the most high profile user of the technology. The form it used was developed by Herman Hollerith — hence the alternate names IBM or Hollerith cards — for the 1890 US Census; his Tabulating Machine Company subsequently became IBM.
The most common size of card could store around 160 characters, although many permutations were used.