ENIAC and Manchester Baby: 30 tons, 5,000 solder joints, and a program in memory

ENIAC, short for Electronic Numerical Integrator and Computer, was the first programmable, electronic, general-purpose digital computer. Completed in 1945, it was designed by John Mauchly and J. Presper Eckert for the United States Army Ballistic Research Laboratory, which later became part of the Army Research Laboratory. The machine's first program was not artillery tables. It was a feasibility study of a thermonuclear weapon.

The concept took shape in June 1941, when the army computed firing tables for artillery using Friden calculators and differential analyzers under Mauchly's supervision. In August 1942, he proposed a fully electronic computing machine. The army awarded the University of Pennsylvania a six-month research contract worth $61,700. The construction contract was signed on 5 June 1943. Work began in secret at the Moore School of Electrical Engineering under the code name "Project PX," with John Grist Brainerd as chief engineer. Herman Goldstine persuaded the army to fund the project.

ENIAC was completed in 1945 and first put to practical use on 10 December 1945. The machine was formally dedicated at the University of Pennsylvania on 15 February 1946. It cost $487,000, equivalent to about $7 million in 2024. The press called it a "giant brain." It ran roughly a thousand times faster than electromechanical machines. The army formally accepted it in July 1946. In 1947, it was moved to Aberdeen Proving Ground in Maryland, where it operated continuously until 1955.

How much of it there was

At the end of its service in 1955, ENIAC contained 18,000 vacuum tubes, 7,200 crystal diodes, 6,000 relays, 70,000 resistors, 10,000 capacitors, and about 5 million hand-soldered connections. It weighed over 30 short tons (27 metric tons), stood about 3 metres high, 1 metre deep, and 30 metres long. It occupied 28 square metres and drew 150 kilowatts. Input data went in via an IBM card reader, and results came out on a card punch from the same company. Much of the programming fell to the women mathematicians: Jean Jennings, Marlyn Wescoff, Ruth Lichterman, Betty Snyder, Frances Bilas, and Kay McNulty. In 1997, the six ENIAC programmers were inducted into the Women in Technology International Hall of Fame. In 1946, the researchers left the university and founded the Eckert–Mauchly Computer Corporation.

Manchester, 21 June 1948

The Manchester Baby, also called the Small-Scale Experimental Machine, was the first electronic computer with a program stored in memory. Frederic C. Williams, Tom Kilburn, and Geoff Tootill built it at Victoria University of Manchester. They ran the first program on 21 June 1948. The machine was not designed as a practical computing tool. It was a test bed for the Williams tube, the first truly randomly addressable memory. It had a 32-bit word and a memory capacity of 32 words, or 1,024 bits. Because it was meant to be the simplest possible computer with a stored program, the hardware implemented only subtraction and negation. The remaining operations were carried out in software. The first of the three programs written for it determined the largest proper divisor of 2 to the power of 18 (262,144), testing every number downwards in turn. The program consisted of 17 instructions and ran for about 52 minutes before reaching the correct result of 131,072. It executed roughly 3.5 million operations, giving an effective speed of about 1,100 instructions per second. Once the Baby proved the design was feasible, the university started work on a full-scale machine, the Manchester Mark 1. This quickly became the prototype for the Ferranti Mark 1, the first commercially available general-purpose computer. Earlier, on 12 May 1941, Konrad Zuse publicly demonstrated the Z3. It was the first working programmable, fully automatic computer with binary arithmetic, but without the conditional branching characteristic of a Turing machine.