- 1943- J. Presper Eckert and John Mauchly begin construction of the Electronic Numerical Integrator And Computer (ENIAC), the first general-purpose electronic digital calculator. The ENIAC is considered the first electronic computer and was used to calculate ballistic firing tables during World War II.
- The Colossus, which was a programmable, digital machine also considered by some to be the first electronic computer, became operational in England.
- 1944- The relay-based Harvard-IBM MARK I, a program-controlled, large-scale calculating machine built by a team led by Howard Aiken, goes to work during World War II providing essential calculations for the U.S. Navy. Grace Hopper becomes its first programmer.
- 1947- The tranresister or transistor is invented by John Bardeen, Walter Brattain, and William Shockley at the AT&T Bell Telephone Laboratories. Transistor is less breakable, quicker, uses less power, and produces less heat than the vacuum tube.
- 1948- A big problem with the computers designed so far is the lack of storage. Andrew Donald Booth creates magnetic drum memory. It is two inches long and two inches wide and capable of holding 10 bits per inch.