ITPEC FE Morning October 2019 Question 11
ITPEC FE Morning October 2019 — Question 11 of 80
CPI (Cycles Per Instruction) — calculate average clock cycles needed per instruction.
Formula: CPI = Clock Rate ÷ Instructions Per Second
Given:
- Clock rate: 2.4 GHz = 2.4 × 10⁹ cycles/sec
- Throughput: 1 billion = 1 × 10⁹ instructions/sec
Calculation:
- CPI = 2.4 × 10⁹ / 1 × 10⁹ = 2.4
Answer: c) 2.4
Why not others:
- (a) 0.04 — would mean less than 1 cycle per instruction (unrealistic for average CPI)
- (b) 0.12 — same issue, sub-cycle execution
- (d) 25 — would indicate extremely slow execution per instruction
Key rule: CPI = total cycles ÷ total instructions. If given clock rate and throughput, just divide clock rate by instructions per second.
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