Early computers, such as the ENIAC, used vacuum tubes - similar to light bulbs - to do calculations and took several people to operate.

Vacuum tubes were replaced by transistors - a type of electronic switch - invented by William Shockley, John Bardeen and Walter Brattain at Bell Labs.

The first working transistor was shown off just before Christmas in 1947, but was only revealed to the public six months later.

The first commercial product to contain a transistor was the Sonotone 1010 hearing aid, released five years after the transistor was invented.

The invention of the transistor ushered in the development of the integrated circuit,- the forerunner of today's silicon chips. The first demonstration was made by Jack Kilby in 1958.

In 1965 the Intel co-founder Gordon Moore, writing in Electronics magazine, correctly predicted that the number of transistors on a chip would double every year.

The steady increase in power of silicon chip ushered in a new era of personal computing, with machines such as the Apple 1 being built by enthusiastic hobbyists.

Today's chips contain millions of transistors and are used in everything from mobile phones and computers to cars and planes.