ENIAC THE FIRST PROGRAM

ENIAC (/ˈɛniæk/; Electronic Numerical Integrator and Computer)was the first programmable, electronic, general-purpose digital computer. It was Turing-complete, and able to solve "a large class of numerical problems" through reprogramming.

Although ENIAC was designed and primarily used to calculate artillery firing tables for the United States Army's Ballistic Research Laboratory (which later became a part of the Army Research Laboratory), its first program was a study of the feasibility of the thermonuclear weapon.

ENIAC was completed in 1945 and first put to work for practical purposes on December 10, 1945.

ENIAC was formally dedicated at the University of Pennsylvania on February 15, 1946 and was heralded as a "Giant Brain" by the press. It had a speed on the order of one thousand times faster than that of electro-mechanical machines; this computational power, coupled with general-purpose programmability, excited scientists and industrialists alike. The combination of speed and programmability allowed for thousands more calculations for problems, as ENIAC calculated a trajectory in 30 seconds that took a human 20 hours (allowing one ENIAC hour to displace 2,400 human hours). The completed machine was announced to the public the evening of February 14, 1946 and formally dedicated the next day at the University of Pennsylvania, having cost almost $500,000 (approximately equivalent to $7,195,000 in 2019). It was formally accepted by the U.S. Army Ordnance Corps in July 1946. ENIAC was shut down on November 9, 1946 for a refurbishment and a memory upgrade, and was transferred to Aberdeen Proving Ground, Maryland in 1947. There, on July 29, 1947, it was turned on and was in continuous operation until 11:45 p.m. on October 2, 1955. ENIAC's design and construction was financed by the United States Army, Ordnance Corps, Research and Development Command, led by Major General Gladeon M. Barnes. The total cost was about $487,000, equivalent to $7,195,000 in 2019. The construction contract was signed on June 5, 1943; work on the computer began in secret at the University of Pennsylvania's Moore School of Electrical Engineering the following month, under the code name "Project PX", with John Grist Brainerd as principal investigator. Herman H. Goldstine persuaded the Army to fund the project, which put him in charge to oversee it for them.

ENIAC was designed by John Mauchly and J. Presper Eckert of the University of Pennsylvania, U.S. The team of design engineers assisting the development included Robert F. Shaw (function tables), Jeffrey Chuan Chu (divider/square-rooter), Thomas Kite Sharpless (master programmer), Frank Mural (master programmer), Arthur Burks (multiplier), Harry Huskey (reader/printer) and Jack Davis (accumulators). Significant development work was undertaken by the ENIAC women programmers: Jean Jennings, Marlyn Wescoff, Ruth Lichterman, Betty Snyder, Frances Bilas, and Kay McNulty. In 1946, the researchers resigned from the University of Pennsylvania and formed the Eckert-Mauchly Computer Corporation.

ENIAC was a modular computer, composed of individual panels to perform different functions. Twenty of these modules were accumulators that could not only add and subtract, but hold a ten-digit decimal number in memory. Numbers were passed between these units across several general-purpose buses (or trays, as they were called). In order to achieve its high speed, the panels had to send and receive numbers, compute, save the answer and trigger the next operation, all without any moving parts. Key to its versatility was the ability to branch; it could trigger different operations, depending on the sign of a computed result. ENIAC could be programmed to perform complex sequences of operations, including loops, branches, and subroutines. However, instead of the stored-program computers that exist today, ENIAC was just a large collection of arithmetic machines, which originally had programs set up into the machine by a combination of plugboard wiring and three portable function tables (containing 1200 ten-way switches each).The task of taking a problem and mapping it onto the machine was complex, and usually took weeks. Due to the complexity of mapping programs onto the machine, programs were only changed after huge numbers of tests of the current program. After the program was figured out on paper, the process of getting the program into ENIAC by manipulating its switches and cables could take days. This was followed by a period of verification and debugging, aided by the ability to execute the program step by step. A programming tutorial for the modulo function using an ENIAC simulator gives an impression of what a program on the ENIAC looked like.

ENIAC's six primary programmers, Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman, not only determined how to input ENIAC programs, but also developed an understanding of ENIAC's inner workings.The programmers were often able to narrow bugs down to an individual failed tube which could be pointed to for replacement by a technician