<b>Punch Cards In, Punch Cards Out</b>
The ENIAC, among other early electronic computers, used Hollerith punched cards as both input and output. To write a program, an operator typed on a typewriter-like machine that encoded the instructions into a pattern of holes punched into a paper card. A person then dropped a stack of cards into the computer, which read and ran the program. For output, the computer punched encoded results onto blank punch cards, which operators then had to decode with a device like the IBM 405 tabulator (shown at right), which tallied and printed card values onto sheets of paper.
Photos: Computer History Museum, IBM, Benj Edwards