The identity of the first digital computer is a topic that has been debated, both in terms of the facts and in 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 1973 court case. It was not a programmable computer, meaning it does not fall into the category of what most people would call a computer today.
To qualify as the first digital computer, a machine would have had to meet two definitions. A computer is a machine that can carry out a series of operations, either mathematical or logical. A digital computer is one that uses numerical values for its operations, usually through binary code that expresses all data through either a 0 or a 1. In contrast, 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.
From a legal perspective, two machines made a claim to be the first digital computer. One was 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, which led to a common belief that ENIAC had been first and allowed the creators of ENIAC to take out a patent. In 1973 this patent was deemed invalid by a US district court. This ruling officially noted the ABC as the first electronic digital computer.
It can be argued that the ABC was not a true computer, however. This is because it was not programmable, meaning it could only perform one set of functions, rather like a pocket calculator. The first known programmable computer was the Z3, produced by German engineer Konrad Zuse in 1941. This was arguably not a digital computer though; it used electromechanics in the form of magnetic switches.
The first digital computer that was fundamentally the same in 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 in a very slow manner. The Manchester machine was purely an experiment to prove the concept. A year later the Electronic Delay Storage Automatic Calculator in Cambridge, England, became the first programmable computer used for commercial purposes.