RISC vs CISC Architectures Quiz Quiz

Explore the core distinctions between RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) architectures with these insightful questions. Assess your understanding of instruction sets, execution efficiency, design philosophy, and practical examples in computer architecture.

1. Instruction Set Size Comparison

   Which statement best describes the instruction set size of RISC compared to CISC architectures?

   1. RISC architectures feature a smaller, more uniform instruction set than CISC.
   2. RISC and CISC always use the exact same number of instructions.
   3. RISC architectures have significantly larger instruction sets than CISC.
   4. RISC instruction sets contain many complex instructions with multiple steps.

   Explanation: RISC stands for Reduced Instruction Set Computer, which means it employs a smaller, simpler, and more uniform set of instructions for efficiency and speed. CISC architectures, on the other hand, use larger and more complex instruction sets to perform multifaceted operations. Saying RISC has a significantly larger set is incorrect, and while some instructions can be complex, they are more typical in CISC. The idea that both always use the same number of instructions is also false.

2. Execution Cycles

   In terms of execution cycles, how do most instructions in RISC architectures behave compared to CISC?

   1. Most RISC instructions execute in a single clock cycle, while CISC instructions may require multiple cycles.
   2. CISC architectures seldom use multi-cycle instructions.
   3. Most RISC instructions require several cycles, unlike CISC which always use one cycle.
   4. RISC instructions are mostly microcoded, leading to slow execution.

   Explanation: RISC instructions are designed to execute most operations within one clock cycle, promoting predictability and efficiency. CISC instructions, due to their complexity, might take multiple cycles to complete. The claim that RISC instructions require several cycles is incorrect, as is the idea that they are microcoded, which is typically associated with CISC. Saying CISC seldom uses multi-cycle instructions ignores their inherent complexity.

3. Design Philosophy

   What is a primary design goal of RISC architectures compared to CISC?

   1. To minimize all forms of processor cache usage
   2. To simplify hardware and optimize for fast instruction pipelining
   3. To maximize the number of instructions performed by single commands
   4. To use as many microoperations as possible for memory efficiency

   Explanation: RISC aims to have simple instructions that execute quickly, enabling efficient pipelining and streamlined hardware design. CISC focuses on maximizing instruction functionality per instruction, not RISC. Minimizing processor cache usage is not a RISC design goal, and using many microoperations for memory efficiency aligns more with CISC design.

4. Instruction Complexity Example

   Given the task of multiplying two numbers stored in memory, how would RISC and CISC generally differ?

   1. CISC cannot directly access memory locations for arithmetic.
   2. RISC would use a single complex instruction, similar to CISC.
   3. RISC would use multiple simple instructions, while CISC might use one complex instruction.
   4. Both RISC and CISC would require the same number of memory fetch cycles.

   Explanation: RISC typically requires breaking down the operation into several steps, such as loading values into registers before performing arithmetic. CISC may offer a single multipurpose instruction to multiply directly from memory locations. They don’t use the same number of cycles; RISC focuses on simplicity. It’s incorrect that CISC cannot access memory directly, as such operations are central to it.

5. Addressing Modes

   How does the number of addressing modes typically differ between CISC and RISC architectures?

   1. RISC supports more varied addressing modes than CISC.
   2. CISC architectures usually support more addressing modes than RISC.
   3. Neither architecture uses memory addressing in operations.
   4. RISC and CISC both always use only immediate addressing.

   Explanation: CISC designs often include a rich variety of addressing modes, allowing for flexible access to memory and operands. RISC typically employs fewer, more straightforward addressing modes to keep instructions simple. While immediate addressing is present in both, they don't exclusively use it. Both RISC and CISC architectures employ memory addressing; it is not ignored by either type.