ITPEC FE Subject A October 2024 Question 8
ITPEC FE Subject A October 2024 — Question 8 of 60
MIPS Calculation — compute CPU performance from an instruction mix.
Given instruction mix:
- •Register-to-register:
0.3 µs,30% - •Register-to-memory:
0.6 µs,50% - •Conditional branch:
0.1 µs,20%
Step 1 — weighted average execution time:
0.3 × 0.3 + 0.6 × 0.5 + 0.1 × 0.2 = 0.09 + 0.30 + 0.02 = 0.41 µs
Step 2 — convert to MIPS:
MIPS = 1 / average_time_in_µs = 1 / 0.41 ≈ 2.44
Why it works: 1 second = 10⁶ µs, MIPS = 10⁶ instructions/sec ÷ 10⁶ = 1 / T(µs)
Why not others:
- (a) 0.03 — unit conversion error
- (b) 0.41 — this is the average time, not MIPS (common trap)
- (d) 35.00 — incorrect calculation
Key rule: MIPS = 1 / weighted_average_time_in_µs. The µs and "millions" cancel out.
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