ITPEC FE Morning October 2019 Question 11
Topic: Computer ComponentAlso asked in April 2022
Which of the following is the average cycles per instruction (CPI) of a computer that can execute 1 billion instructions per second with a clock rate of 2.4 GHz?
Explanation
2.4 — CPI is clock cycles per second divided by instructions per second.
- •Clock: 2.4 GHz = 2.4 × 109 cycles per second
- •Execution: 1 billion = 1 × 109 instructions per second
- •CPI: 2.4 × 109 ÷ (1 × 109) = 2.4 cycles per instruction
Answer (c)
Why not others:
- •(a) 0.04 and (b) 0.12 — a CPI below 1 means more than one instruction per cycle, which at 2.4 GHz would exceed the stated 1 billion instructions per second
- •(d) 25 — at 25 cycles per instruction a 2.4 GHz processor runs only 96 million instructions per second, not 1 billion
Key rule: CPI = clock frequency ÷ instructions per second, and MIPS = clock frequency in MHz ÷ CPI; keep both in the same power of ten.
Computer Component · AI-written, may contain errors
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