An example of ENIAC was the computer created for the military in the 40s which, when completed, took up an entire room.
ENIAC - Computer Definition
(Electronic Numerical Integrator And Computer) The first operational electronic digital computer developed for the U.S. Army by J. Presper Eckert and John Mauchly at the University of Pennsylvania in Philadelphia. Started in 1943, it took 200,000 man-hours and nearly a half million dollars to complete two years later. Programmed by plugging in cords and setting thousands of switches, the decimal-based machine used 18,000 vacuum tubes, weighed 30 tons and took up 1,800 square feet. It cost a fortune in electricity to run; however, at 5,000 additions per second, it was faster than anything else. Initially targeted for trajectory calculations, by the time it was ready to go, World War II had ended. Soon after, it was moved to the army's Aberdeen Proving Grounds in Maryland where it was put to good work computing thermonuclear reactions in hydrogen bombs and numerous other problems until it was dismantled in 1955. An Amazing Machine in 1946 Referring to ENIAC's public introduction in early 1946, The New York Times said "One of the war's top secrets, an amazing machine which applies electronic speeds for the first time to mathematical tasks hitherto too difficult and cumbersome for solution, was announced here tonight." Today, all 1,800 square feet of that machinery fits on the head of a pin. ENIAC proved that the thinking behind electronic computing was sound, and smaller and faster machines were forecast at the dedication ceremony. However, it is doubtful they would have conceived that the entire CPU would be no bigger than a pencil eraser some day. See EDVAC and early computers.