ITPEC FE Morning October 2021 Question 19
ITPEC FE Morning October 2021 — Question 19 of 80
Execution Time with New Compiler — calculate new execution time after changes to instruction count and CPI.
Formula: Execution time = Instruction count × CPI × Clock cycle time
Given:
- Old execution time: 15 seconds
- New compiler: 40% fewer instructions → factor 0.6
- New compiler: CPI increased by 10% → factor 1.1
- Same processor → clock cycle time unchanged
Calculation:
- New time = 15 × 0.6 × 1.1 = 9.9 seconds
Why not others:
- (a) 4.125 — incorrectly reduces both instruction count and CPI
- (b) 6.6 — uses 0.4 instead of 0.6 (takes 40% of instructions, not 60%)
- (c) 9.09 — divides by 1.1 instead of multiplying (treats CPI increase as speedup)
Key rule: "Fewer by X%" means multiply by (1 - X/100). "Increased by Y%" means multiply by (1 + Y/100). Both affect execution time multiplicatively.
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