Live Calculators

Plug in numbers to check your hand-worked answers. Everything updates instantly.

1 · CPU Execution Time

\text{CPU time} = \frac{\text{IC} \times \text{CPI}}{\text{clock rate}}

Instruction count (IC) CPI Clock rate Unit

Total cycles = IC × CPI = 2,000,000,000
CPU time = 1.000 s

2 · Average CPI

\text{Average CPI} = \frac{\sum_i \text{CPI}_i \times \text{Count}_i}{\sum_i \text{Count}_i}

Class	CPI	Count	Cycles
A			5
B			2
C			3

Total cycles = 10, Total instructions = 7
Average CPI = 1.4286

3 · Amdahl's Law

\text{New time} = \text{Unaffected} + \frac{\text{Affected}}{r} \qquad \text{Speedup} = \frac{\text{Old}}{\text{New}}

Old total time Affected part (time) Speed-up factor r

Unaffected (floor) = 20
New time = 20 + 80/16 = 25.000
Overall speedup = 4.000×
Max possible speedup (r → ∞) = 5.000×

Tip: set Old = 100, Affected = 80, r = 16 → speedup 4× (that's worked example WE-9a). Then try r = anything for the multiply problem and watch it approach the 5× ceiling but never cross it.