Final answer:
Third generation computers shrunk in size due to the use of an integrated circuit or microchip. The microprocessor, a key part of this circuit, centralized computing power and sparked the personal computer revolution.
Step-by-step explanation:
Third generation computers became smaller and more reliable by incorporating multiple transistors and electronic circuits on a single tiny silicon chip called an integrated circuit or commonly referred to as a microchip. These integrated circuits enabled the same computer technology that once occupied entire rooms to be condensed into the compact size of early personal computers. The microprocessor, a key innovation within these circuits, centralized a computer's processing power into one chip. This revolutionized computing, leading to the advent of popular models like the Altair 8800, which utilized an Intel microprocessor, and the Apple II, which helped establish Apple's presence in the computer market.