Cache Miss Rate Impact Calculator
Work out cache miss rate impact instantly with clear inputs, formula shown and shareable results.
About Cache Miss Rate Impact Calculator
Average memory access time is hit time plus miss rate times miss penalty. With a 180 cycle penalty even a 3.5% miss rate adds 6.3 cycles — more than the hit time itself — which is why miss rate reduction matters far more than shaving a cycle off L1 latency.
Formula
AMAT
AMAT = hit time + miss rate x miss penalty; CPI added = miss rate x penalty x accesses per instruction
Worked example
With the default values below, Cache Miss Rate Impact Calculator returns Average memory access time of 10.30. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Cache miss rate
- 3.5 %
- Miss penalty
- 180 cycles
- Hit time
- 4 cycles
- Memory accesses per instruction
- 1.3 accesses
Results
- Average memory access time
- 10.30 cycles
- CPI added by misses
- 8.19 cycles
- Stall cycles per 1000 instructions
- 8,190.0 cycles
- Memory share of access time
- 61.17% %
Step by step
- 1Values used
- 2AMAT
- 3Average memory access time= 10.30 cycles
- 4CPI added by misses= 8.19 cycles
- 5Stall cycles per 1000 instructions= 8,190.0 cycles
- 6Memory share of access time= 61.17 %
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why does a small miss rate hurt so much?
Because the penalty is two orders of magnitude larger than a hit. A 1% miss rate at 200 cycles adds 2 cycles to every access on average.
What reduces the penalty rather than the rate?
Multi-level caches, non-blocking caches with hit-under-miss, prefetching, and critical-word-first return from memory.
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