OCR A-Level Computer Science: Processors & Hardware

A processor executes machine code using the fetch-decode-execute (FDE) cycle. It contains the Program Counter (PC), Memory Address Register (MAR), Memory Data Register (MDR), Current Instruction Register (CIR) and Accumulator (ACC), and is connected to main memory by the address bus, data bus and control bus.

(a) Describe one complete fetch-decode-execute cycle, step by step. At each step, name the register(s) involved (PC, MAR, MDR, CIR, ACC) and the bus (address / data / control) that carries the transfer where one applies. [6 marks]

(b) A magazine review claims one processor is "faster" than another. Explain how clock speed, number of cores and amount of cache each affect a CPU's performance. [4 marks]

(c) The processor uses pipelining. State what pipelining does, and give one situation that limits the benefit it provides. [2 marks]

A manufacturer is designing the processor for a wrist-worn fitness smartwatch. The watch must run for several days on a single small battery, continuously sampling heart-rate and motion sensors, counting steps and showing notifications. It runs only the manufacturer's own purpose-built firmware. The design team must decide between a RISC processor and a CISC processor.

Evaluate the use of a RISC processor rather than a CISC processor in this fitness smartwatch. [9 marks]

Two processor designs are described by the Von Neumann architecture and the Harvard architecture.

Compare the Von Neumann and Harvard architectures. Your answer should refer to how each stores and accesses instructions and data, state one advantage of each, and identify one context in which the Harvard architecture is typically used. [6 marks]

A computer's memory is organised as a hierarchy that includes cache, RAM, ROM and virtual memory.

(a) Distinguish between RAM, ROM and cache by stating the purpose of each. [3 marks]

(b) Explain what virtual memory is and give one drawback of relying on it. [2 marks]

A film-production company needs to choose secondary storage for the laptops its camera crew take on outdoor shoots, where the devices are frequently jolted and carried around. The three options are magnetic (HDD), solid-state (SSD) and optical storage.

Compare magnetic, solid-state and optical storage for this use case, referring to speed, durability and cost-per-gigabyte / capacity, and state which you would recommend. [4 marks]

A scientist applies the same calculation to every pixel of millions of large images and finds a GPU completes the task far faster than the CPU. GPUs are an example of SIMD (Single Instruction, Multiple Data) parallel processing.

Explain the difference between SIMD and MIMD processing, and state why a GPU outperforms a CPU on this highly parallel, data-parallel task. [3 marks]