Early computers were large, complex machines designed to perform calculations and process data. The first electronic computer, known as the ENIAC, was developed in the 1940s and could perform thousands of calculations per second. These machines used vacuum tubes and were primarily used for military and scientific purposes. As technology advanced, computers became smaller and more accessible. The introduction of the transistor in the 1950s replaced vacuum tubes, making computers more reliable and energy-efficient. By the 1960s, computers began to be used in businesses and homes, paving the way for the modern computing era.