CPU Performance Metrics: CPI, MIPS, and Throughput Quiz Quiz

Explore your understanding of key CPU performance metrics, including cycles per instruction (CPI), millions of instructions per second (MIPS), and system throughput. This quiz will help you review essential concepts and calculations related to CPU efficiency and performance analysis.

1. CPI Definition

   What does the acronym CPI stand for in the context of CPU performance?

   1. Cycles Per Instruction
   2. Computational Processing Information
   3. Clock Performance Index
   4. Central Processing Interface

   Explanation: Cycles Per Instruction (CPI) measures how many clock cycles the CPU spends executing each instruction on average. 'Clock Performance Index' and 'Computational Processing Information' sound similar but are not standard terms. 'Central Processing Interface' is unrelated to the performance metric discussed here.

2. MIPS Calculation

   If a CPU executes 4 million instructions in 2 seconds, what is its MIPS rate?

   1. 2 MIPS
   2. 0.5 MIPS
   3. 1 MIPS
   4. 8 MIPS

   Explanation: MIPS stands for Millions of Instructions Per Second, so divide 4 million instructions by 2 seconds to get 2 MIPS. 1 MIPS and 0.5 MIPS reflect incorrect calculations. 8 MIPS would require more instructions executed in less time, which is not the case.

3. Throughput in CPUs

   Which term describes the number of programs a processor can complete in a unit of time?

   1. Throughput
   2. Instruction Width
   3. Latency
   4. Frequency

   Explanation: Throughput refers to how many tasks or programs a CPU finishes in a given period, reflecting system productivity. Latency measures response delay, not overall completion. Frequency is the clock speed in hertz. Instruction width refers to the bit-length of instructions, not program completion rate.

4. Interpreting a Low CPI

   If a processor exhibits a lower CPI value, what does this most likely indicate?

   1. It operates at a lower clock speed.
   2. It uses more memory for execution.
   3. It has a slower overall performance.
   4. It completes instructions in fewer clock cycles.

   Explanation: A lower CPI shows that, on average, instructions take fewer cycles, indicating efficient instruction execution. Slower performance or lower clock speed are not necessarily related to low CPI. Memory usage is also irrelevant to the CPI metric.

5. Finding Total CPU Time

   Given 1 million instructions, CPI of 3, and clock rate of 1 GHz, what is the CPU's total execution time?

   1. 0.3 seconds
   2. 3 seconds
   3. 0.0003 seconds
   4. 0.003 seconds

   Explanation: CPU execution time is calculated as (Instruction count × CPI) / clock rate. Here, (1,000,000 × 3) / 1,000,000,000 = 0.003 seconds. The other answers use incorrect arithmetic or misunderstand the units involved.

6. Effect of Increasing Clock Rate

   If the clock rate of a CPU increases and all else remains constant, how does this affect the MIPS value?

   1. MIPS value decreases
   2. MIPS value increases
   3. MIPS is not affected by clock rate
   4. MIPS value stays the same

   Explanation: A higher clock rate allows a CPU to execute instructions faster, boosting the MIPS value if CPI and instruction count are the same. If clock rate decreases, MIPS would decrease. MIPS is directly affected by clock rate, not independent of it.

7. Distinguishing Latency from Throughput

   What does latency mean when evaluating processor performance?

   1. The total number of instructions executed per second
   2. The number of tasks completed in a minute
   3. The average width of executed instructions
   4. The time it takes to finish a single task

   Explanation: Latency is the time from start to completion of one task, indicating responsiveness. The number of instructions per second refers to throughput (MIPS), not latency. Instruction width relates to data size, and tasks per minute is another way to describe throughput.

8. Typical Unit for Throughput

   What is a common unit for measuring throughput in computer systems?

   1. Seconds per task
   2. Tasks per second
   3. Instructions per cycle
   4. Milliseconds per instruction

   Explanation: Throughput is most commonly measured in tasks or programs completed per second, emphasizing rate. Seconds per task is latency, not throughput. Instructions per cycle describes how many instructions are completed each clock cycle, and milliseconds per instruction is another form of latency.

9. Understanding High MIPS Value

   If a processor has a very high MIPS value, what does this typically suggest about its performance?

   1. It always uses less power
   2. It cannot run complex instructions
   3. It necessarily has a low CPI
   4. It executes many instructions quickly

   Explanation: A high MIPS value shows the processor is capable of completing many instructions per second. However, a low CPI is not guaranteed; instruction mix or complexity affects CPI. Power use and ability to run complex instructions are independent of MIPS and are not directly indicated here.

10. CPI Calculation Example

    A CPU processes 5 instructions in 15 clock cycles. What is the CPI?

    1. 7.5
    2. 75
    3. 0.33
    4. 3

    Explanation: CPI is found by dividing total clock cycles by total instructions: 15/5 = 3. 0.33 is an inverted result, 7.5 and 75 are too high and result from incorrect calculations.