A Level Computer Science OCR Practice Exam

What is the primary function of a RISC architecture regarding instruction execution?

1. To run multiple machine cycles per instruction

2. To run a single machine cycle per instruction

3. To optimize instruction size based on data

4. To execute various instruction sizes

The correct answer is: To run a single machine cycle per instruction

The primary function of a RISC (Reduced Instruction Set Computer) architecture is to streamline instruction execution by utilizing a design philosophy that emphasizes simplicity and efficiency. In RISC architectures, the goal is to execute a single machine cycle per instruction, which allows for faster processing speeds and improved overall performance. This single cycle execution is achieved by having a fixed instruction size and a limited set of instructions that can be executed in one clock cycle. By keeping the instruction set simple and consistent, RISC can benefit from a more efficient use of the CPU's pipeline. Pipelining allows multiple instructions to be processed at different stages simultaneously, thus maximizing the throughput of instruction execution. RISC's approach contrasts with architectures that use complex instructions that may take multiple cycles to execute. This design choice prioritizes speed and predictability, leading to better performance in many applications, especially those that favor high instruction throughput. An important aspect of RISC is that it does not generally focus on variable instruction sizes or optimizing instruction size based on the data, nor does it aim to execute various instruction sizes, as seen in CISC (Complex Instruction Set Computer) architectures. By concentrating on uniformity and speed, RISC architectures achieve their primary goal of efficient instruction execution.