text: That depends on how you define the word "computer."\n\nA succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features of modern computers, such as the use of digital electronics (invented by Claude Shannon in 1937) and more flexible programmability. Defining one point along this road as "the first computer" is exceedingly difficult. Notable achievements include the Atanasoff-Berry Computer, a special-purpose machine that used valve-driven (vacuum tube) computation, binary numbers, and regenerative memory; the secret British Colossus computer (1944), which had limited programmability but demonstrated that a device using thousands of valves could be made reliable and reprogrammed electronically; the American ENIAC (1946) — which was one of the first general purpose machine, but still used the decimal system and incorporated an inflexible architecture that meant reprogramming it essentially required it to be rewired and Konrad Zuse's Z machines, with the electromechanical Z3 (1941) being the first working machine featuring automatic binary arithmetic and feasible programability.