Question 4 of 6: Computer-system components and CPU registers

Question 4: Computer-system components and CPU registers (12 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(a) Essential components. A stored-program computer reduces to four essentials, marked below; the remaining items are optional peripherals attached through the I/O ports.

The CPU fetches and executes instructions, memory holds those instructions and their data, the three busses carry addresses, data and control/timing between them, and the I/O ports are the essential doorway to the outside world. A mouse, keyboard, printer, monitor or hard drive is a convenience that plugs into an I/O port; a machine without any of them is still a computer, but a machine missing the CPU, memory, busses or I/O is not.

(b) Microprocessor vs microcontroller. A general-purpose microprocessor (µP) is essentially a CPU on a chip: it brings the ALU, register file and control unit, but memory, I/O, timers and other peripherals must be added externally across the system busses. It is optimised for raw computing throughput and flexibility, at higher clock speed, power and board cost, and is the heart of a general-purpose computer. A microcontroller (µC) integrates the CPU together with program memory (Flash/ROM), data memory (RAM), parallel and serial I/O ports, timers/counters and often ADCs on a single chip. It is a self-contained "computer on a chip" tuned for dedicated embedded control — low cost, low power and small footprint — rather than for maximum performance. In short: a µP maximises computing power and needs external support chips; a µC trades peak performance for on-chip integration, economy and real-time I/O.

(c) CPU registers. Each described role maps to a standard register: