reading cards
Babbage, probably inspired by the control mechanism in Jacquard's fabric looms, proposed using punched cards in the Analytical Engine for three purposes: Operation cards that hold the "instructions" for the computer Variable cards that specify which locations in the Store (memory) should be read or written Number cards that hold constants needed for the calculation His card reading mechanisms most often used a six-sided cylindrical object he called a "prism" that the cards were wrapped around, draping down below for as many cards as needed. The front-facing side of the prism was advanced against a serial of pins or rods, which would either be pushed by the card or not, depending on whether there was a hole in that position. The movement of those rods would control other mechanisms in the machine. (Remember: you can click to get larger versions of all the images.) The rods shown here (drawing A/094 from August 14, 1841) are in pairs, linked so that when one goes...