( 1904 ) John Ambrose Fleming invented the vacuum diode, in 1904. This invention, which he called oscillation valve, laid the groundwork for the construction of the first electronics switching component. It contained two electrodes: the cathode and anode. The cathode was a heater filament that caused the emission of electrons. The anode was a plate that attracted electrons. If a positive voltage was applied
to the plate, a current passed through the device (closed switch), whereas if the voltage was negative, the current was blocked (open switch).

Lee DeForest perfected Fleming’s work in 1906 by adding a third electrode (grid) to the original tube and created the triode, which he called audion. It took several years to improve the vacuum and make
these devices reliable. They were not used in computer construction until 1943.