CPI (cycles per instruction)
Beginner
On average, how many clock ticks the processor needs to finish one command.
Novice
Cycles per instruction: the average number of clock ticks a processor takes per instruction. . Anything that makes the processor wait, such as a wrong guess about a branch or a cache miss, raises CPI. Its inverse, instructions per cycle, is called IPC.
Expert
Usually broken into a base CPI plus a stall term for each cause (branch mispredictions, misses at each memory level, busy units). Deeper pipelines raise frequency and CPI together, so compare designs on , never on either alone.