A computer is a machine that stores information, does calculations, and follows instructions called programs to complete tasks. The word comes from “compute,” meaning to calculate, because early computers were built mainly to solve math problems that would take humans years to finish by hand.

Modern computers work by processing millions of tiny electrical signals every second. They can write documents, play music, display videos, connect to the internet, run games, and control everything from traffic lights to spacecraft. A smartphone is actually a powerful computer small enough to fit in your pocket. Laptops, desktops, and tablets are all computers too.

What makes computers special is their ability to follow step-by-step instructions extremely fast and without getting tired or making careless mistakes. A programmer writes these instructions in special languages that tell the computer exactly what to do, like a recipe tells a cook how to make a cake. These programs let computers do wildly different jobs: the same machine that helps you write a story could also edit photos, play chess, or video chat with your grandmother across the country.

Before electronic computers existed, the word computer referred to a person whose job was doing calculations, often using mechanical aids like adding machines. During World War II, rooms full of human computers (mostly women) did complex math for engineering and military projects. Today's electronic computers can do in seconds what those human computers needed weeks to accomplish.