Another system was designed to predict spring floods in the Mississippi River basin.

Electronic Computers

During World War II a team of scientists and mathematicians, working at Bletchley Park, north of London, created one of the first all-electronic digital computers: Colossus. By December 1943, Colossus, which incorporated 1,500 vacuum tubes, was operational. It was used by the team headed by Alan Turing, in the largely successful attempt to crack German radio messages enciphered in the Enigma code.
Independently of this, in the United States, a prototype electronic machine had been built as early as 1939, by John Atanasoff and Clifford Berry at Iowa State College. This prototype and later research were completed quietly and later overshadowed by the development of the Electronic Numerical Integrator And Computer (ENIAC) in 1945. ENIAC was granted a patent, which was overturned decades later, in 1973, when the machine was revealed to have incorporated principles first used in the Atanasoff-Berry Computer (ABC).

ENIAC contained 18,000 vacuum tubes and had a speed of several hundred multiplications per minute, but originally its program was wired into the processor and had to be manually altered. Later machines were built with program storage, based on the ideas of the Hungarian-American mathematician John von Neumann. The instructions, like the data, were stored within a "memory", freeing the computer from the speed limitations of the paper-tape reader during execution and permitting problems to be solved without rewiring the computer. See Von Neumann Architecture.

The use of the transistor in computers in the late 1950s marked the advent of smaller, faster, and more versatile logical elements than were possible with vacuum-tube machines. Because transistors use much less power and have a much longer life, this development alone was responsible for the improved machines called second-generation computers. Components became smaller, as did inter-component spacings, and the system became much less expensive to build.

Integrated Circuits

Late in the 1960s the integrated circuit, or IC, was introduced, making it possible for many transistors to be fabricated on one silicon substrate, with interconnecting wires plated in place. The IC resulted in a further reduction in price, size, and failure rate. The microprocessor became a reality in the mid-1970s with the introduction of the large-scale integrated (LSI) circuit and, later, the very large-scale integrated (VLSI) circuit (microchip), with many thousands of interconnected transistors etched into a single silicon substrate.
To return, then, to the switching capabilities of a modern computer: computers in the 1970s were generally able to handle eight switches at a time.