Computers had been in development since the 19th century, when Charles Babbage was trying to perfect his impossibly huge, all mechanical "difference engine". World War II accelerated the development of an electronic version when fast computing machines were needed to help solve the complex equations created by bomb targeting and the development of the atomic and hydrogen bombs.

England's top-secret Colossus, designed by a team headed by Alan Turing and used to decipher German codes, had used 1,500 vacuum tubes and is considered the first all-electronic calculating machine. At the same time, a team of engineers from International Business Machines (IBM) led by Howard Aiken built the Automatic Sequence Controlled Calculator (ASCC) at Harvard, later dubbed the Mark I.

Between 1937 and 1942, John Vincent Atanasoff and Clifford Berry built their Atanasoff-Berry Computer (ABC) at Iowa State University, now considered the first all-electronic digital computer.

In 1946, what was considered the first true computer, the Pentagon-funded, vacuum tube-powered, room-sized ENIAC (Electronic Numerical Integrator and Computer) was demonstrated publicly by its inventors, John Mauchly and John Presper Eckert, in Philadelphia. But Mauchly and Eckert used – and took credit for – the basic concepts of the ABC to build ENIAC, and it would be nearly 30 years before Atanasoff-Berry would receive the patents for their work.

In 1944, Hungarian-born Princeton mathematician John von Neumann conceived stored programming, otherwise known as software. In June 1948, British researchers Tom Kilburn and Freddie Williams working at Manchester University took advantage of von Neumann's concepts and invented "The Baby", the first stored-program computer.

But perhaps the most famous of these early computers was the UNIVAC (Universal Automatic Computer), the first widely used commercial computer. The UNIVAC I was built by the Eckert-Mauchly Computer Corp., which was bought by Remington Rand just before the UNIVAC went on sale. About the size of a small garage and containing around 5000 vacuum tubes, a total of 46 machines were built and cost $1 million each. UNIVAC first was used by the U.S. Census Bureau on June 14, 1951.

In November 1952, CBS famously used a UNIVAC to correctly predict the outcome of the Eisenhower-Stevenson presidential contest on election night, but didn't release the information in fear of affecting the outcome.

Throughout the late 1940s and 1950s, the military and commercial companies, most prominently an already well-known typewriter and adding machine company called IBM, continued computer development. Soon, large computers became omnipresent throughout the military and business worlds. But no one figured anyone would want a computer at home.