A Level Computer Science OCR Practice Exam

What is a common characteristic of CISC compared to RISC?

1. CISC has fewer memory addressing methods

2. CISC uses a more complex instruction set

3. CISC operates at a higher clock speed

4. CISC is designed for mobile use

The correct answer is: CISC uses a more complex instruction set

The hallmark characteristic of CISC (Complex Instruction Set Computing) architectures is that they utilize a more complex instruction set. This structure allows CISC processors to execute multi-step operations or high-level functions with a single instruction, potentially reducing the number of instructions needed for a particular programming task. The complexity of the instruction set means that CISC processors can handle a greater variety of operations directly in hardware, making them well-suited for certain applications where the richness of the instruction set provides advantages in efficiency of coding and memory usage. Unlike RISC (Reduced Instruction Set Computing), which is designed to execute a smaller set of simpler instructions rapidly, CISC architectures focus on maximizing the number of operations that can be accomplished in a single instruction, thus supporting a more sophisticated programming model. This approach can lead to overall efficiency gains in specific contexts, particularly in environments that benefit from complex instructions, such as those requiring frequent access to manipulation of data structures.