EASA Module 5 · 5.6 / 5.7 Computer Structure & Microprocessors
A processor does one thing, endlessly: fetch the instruction the program counter points at, decode it, execute it. Step through the cycle and watch which bus carries what — the address bus always outward from the CPU, the data bus both ways.
The program counter holds the address of the next instruction — the instruction register holds the one being executed now. That distinction is a standard exam question. Note the bus directions: the address bus is unidirectional, driven only by the CPU; the data bus is bidirectional; the control bus carries the read/write, clock and interrupt lines that make each transfer happen at the right moment.