In 1906 the Vacuum tube was developed by Lee De Forest. This was important because it provided an electrically controlled switch; a necessissity for digital electronic computers.
In 1937 the English mathematician Alan Turing develops the idea of a universal machine that can solve any computable task. The Turing Machine, as it is now called, is a useful tool to help computer scientists understand what sorts of problems are solvable. Turing's machine was developed long before a general purpose computer became available.
