Punched card

Punched cards were a very popular medium for input/output and data storage in the early period of computer usage. Physically, they were stiff, thin cards; data was stored by the presence of absence of holes punched in pre-determined locations.

They were actually a hangover from a pre-electronic stage of data processing; Herman Hollerith pioneered the use of cards for data storage for the 1890 U.S. census, and IBM became a world-wide colossus before World War II on its dominance of card processing.

A number of different formats were used over time. but the most popular by far was IBM's format, introduced in 1928: they were 7-3⁄8 by 3-1⁄4 inches in size, with rectangular holes in 80 columns of 12 rows.

In the pre-electronic era brushes were used to sense the presence or absence of a hole; later on, optical sensors were common.