It consisted of nearly 20,000 vacuum tubes, 10,000 capacitors, and 70,000 resistors. The ENIAC is a great example of a first-generation computer. Some of the first-generation computers took up an entire room. Vacuum tubes were larger components and resulted in first-generation computers being quite large in size, taking up a lot of space in a room. Vacuum tubes were widely used in computers from 1940 through 1956.