15th February 1946: ENIAC, the First Programmable General-Purpose Electronic Digital Computer

Eighteen months after entering the Second World War, the United States Army, Ordnance Corps, Research and Development Command agreed to fund the construction of a machine to compute values for artillery range tables. They approved a design by John Mauchly and J. Presper Eckert from the University of Pennsylvania who began to build the enormous computer in secret in July 1943. Sited in the basement of the University’s Moore School of Electrical Engineering, the enormous machine consisted of 40 panels arranged in a U-shape around the walls. These housed tens of thousands of vacuum tubes, resistors, capacitors, and relays that consumed 150 kW of electricity while creating so much heat that the computer needed its own air conditioning system. Nevertheless it was able to complete up to 5,000 mathematical calculations per second. This made it possible to solve multiple complex problems each hour, whereas even a skilled human could take a day or more for just one. ENIAC was programmed using a combination of a wired plugboard and switches. These programs could take days to plan on paper and, while it often took even longer to input them into the machine, the electronic speed at which the finished program ran saved significant time compared to computers that were controlled by card readers or other mechanical input devices. Although work began on the computer in 1943, it wasn’t fully operational until early 1946 and was formally dedicated on 15 February. ENIAC was soon put to use running calculations to help build a hydrogen bomb, and continued to operate until 1955.