The early components that would contribute to the development of the computer were invented back in 1939, when Hewlett Packard invented their first product.
"Their first product was the HP 200A Audio Oscillator, which rapidly becomes a popular piece of test equipment for engineers."
The full history of the development of the different components that went into the emergence of the first computers is long and complex.
The two websites listed below go into great detail about component parts, their significance and the inventors who deserve credit for advancing the effort. Please look at these sites to get a full and thorough understanding of the history.