What are punched cards?

Punched cards are thick paper rectangles with tiny holes that computers use to remember what to do, much like a vinyl record holds music.

Long ago, before screens and keyboards, machines needed a way to store instructions. Imagine a sheet of sturdy paper covered in a grid of empty circles. To tell the computer to "add" two numbers, you punch out specific circles with a metal stylus. The machine has tiny needles that sweep across the card. If a needle finds a hole, it slips through and sends an electrical signal. It is like a game of whack-a-mole where the holes are the winners.

Think of a punched card like a chocolate bar with many small squares. Each square can either be broken off (a hole) or left intact (no hole). A single row might say "open door," while the row next to it says "close window." By punching different patterns, you program the machine to perform tasks in order. Factories used them to control sewing machines, and early calculators used them to add up big numbers for taxes. You could stack a deck of these cards like playing cards, and the computer would read each one until all the jobs were done.

These cards are heavy and take up space. Carrying a million instructions means carrying millions of paper scraps! Today, your laptop stores those same instructions in tiny electronic switches that are faster and smaller than a grain of sand. But punched cards were the grandparents of modern computing, teaching machines how to think step by step before we had digital screens to guide us.