What is the primary function of an operational amplifier's internal transistors?

Operational amplifiers use internal transistors to amplify tiny differences between their two input pins into a much larger voltage at the output. The first transistor pair acts as a differential amplifier, turning a millivolt‑level difference into a larger signal while keeping the inputs high‑impedance. Cascaded transistor stages then boost this signal, giving the op‑amp its high gain. Finally, the last transistor stage drives the output load with low impedance. For example, a 1 mV difference at the inputs can produce a 10 V output in a typical op‑amp.