John Adam Presper "Pres" Eckert, Jr. (April 9, 1919 – June 3, 1995) was an American electrical engineer and computer pioneer. With John Mauchly he invented the first general-purpose electronic digital computer (ENIAC), presented the first course in computing topics (the Moore School Lectures), founded the first commercial computer company (the Eckert–Mauchly Computer Corporation), and designed the first commercial computer in the U.S., the UNIVAC, which incorporated Eckert's invention of the mercury delay line memory.
Dr. John Mauchly, then chairman of the physics department of nearby Ursinus College, was a student in the summer electronics course, and the following fall secured a teaching position at the Moore School. Mauchly's proposal for building an electronic digital computer using vacuum tubes, many times faster and more accurate than the differential analyzer for computing ballistics tables for artillery, caught the interest of the Moore School's Army liaison, Lieutenant Herman Goldstine, and on April 9, 1943 was formally presented in a meeting at Aberdeen Proving Ground to director Colonel Leslie Simon, Oswald Veblen, and others. A contract was awarded for Moore School's construction of the proposed computing machine, which would be named ENIAC, and Eckert was made the project's chief engineer. ENIAC was completed in late 1945 and was unveiled to the public in February, 1946.
ENIAC (Electronic Numerical Integrator And Computer) was the first electronic general-purpose computer. It was Turing-complete, digital, and capable of being reprogrammed to solve "a large class of numerical problems". Though ENIAC was designed and primarily used to calculate artillery firing tables for the United States Army's Ballistic Research Laboratory, its first programs included a study of the feasibility of the hydrogen bomb.
When ENIAC was announced in 1946, it was heralded in the press as a "Giant Brain." It had a speed of one thousand times that of electro-mechanical machines. This computational power, coupled with general-purpose programmability, excited scientists and industrialists.
ENIAC contained 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors and around 5 million hand-soldered joints. It weighed more than 30 short tons (27 t), was roughly 8 by 3 by 100 feet (2.4 m × 0.9 m × 30 m), took up 1800 square feet (167 m2), and consumed 150 kW of power. This led to the rumor that whenever the computer was switched on, lights in Philadelphia dimmed. Input was possible from an IBM card reader, and an IBM card punch was used for output. These cards could be used to produce printed output offline using an IBM accounting machine, such as the IBM 405.
ENIAC used ten-position ring counters to store digits; each digit used 36 vacuum tubes, 10 of which were the dual triodes making up the flip-flops of the ring counter. Arithmetic was performed by "counting" pulses with the ring counters and generating carry pulses if the counter "wrapped around", the idea being to emulate in electronics the operation of the digit wheels of a mechanical adding machine.
ENIAC had twenty ten-digit signed accumulators which used ten's complement representation and could perform 5,000 simple addition or subtraction operations between any of them and a source (e.g., another accumulator, or a constant transmitter) every second. It was possible to connect several accumulators to run simultaneously, so the peak speed of operation was potentially much higher due to parallel operation.