st. Throughout the first
             half of the 20th century, vacuum tubes were used to conduct, modulate and
             amplify electrical signals. They made possible a variety of new products
             including the radio and the computer. However vacuum tubes had some
             inherent problems. They were bulky, delicate and expensive, consumed a
             great deal of power, took time to warm up, got very hot, and eventually
             burned out. The first digital computer contained 18,000 vacuum tubes,
             weighed 50 tins, and required 140 kilowatts of power.
             By the 1930's, researchers at the Bell Telephone Laboratories were
             looking for a replacement for the vacuum tube. They began studying the
             electrical properties of semiconductors which are non-metallic substances,
             such as silicon, that are neither conductors of electricity
             ...