The identity of the first digital computer is a matter of debate, both in terms of fact and definition. The closest thing to an official answer is the Atanasoff-Berry computer, or ABC, which was declared the first electronic digital computer in a court case in 1973. It was not a programmable computer, which means it does not fall into the category of what today most people would call it a computer.
The slide rule is a mechanical analog computer.
To qualify as the first digital computer, a machine would have to meet two definitions. A computer is a machine that can perform a series of operations, whether mathematical or logical. A digital computer is one that uses numerical values for its operations, usually through binary code that expresses all data through 0 or 1. Instead, an analog computer uses a physical property. Examples include a slide rule or a machine that uses the flow of water to simulate the flow of money in an economy.
The first analog electrical computers filled entire rooms.
From a legal standpoint, two machines claimed to be the first digital computer. One was the Electronic Numerical Integrator and Computer, or ENIAC, which was built between 1943 and 1946. It was used to calculate the flight paths of projectile missiles for the United States Army.
The second claimant was the Atanasoff-Berry computer, built between 1937 and 1942 at Iowa State College. It was not widely publicized, leading to a common belief that ENIAC had been the first and allowing the creators of ENIAC to obtain a patent. In 1973, this patent was declared invalid by a US District Court. This decision officially named the ABC as the first digital electronic computer.
However, it could be argued that the ABC was not a true computer. This is because it was not programmable, meaning it could only perform one set of functions, like a pocket calculator. The first known programmable computer was the Z3, produced by the German engineer Konrad Zuse in 1941. It was certainly not a digital computer; Electromechanics used in the form of magnetic switches.
The first digital computer that had fundamentally the same concept as modern machines was the Manchester Small-Scale Experimental Machine, completed in Manchester, England, in 1948. It allowed users to input a new program, albeit very slowly. The Manchester machine was purely a proof of concept experiment. A year later, the Automatic Electronic Storage Delay Calculator in Cambridge, England, became the first programmable computer used for commercial purposes.
