seconds instructions Example cycles instruction seconds cycle program program constant trade-off Suppose we have two implementations of the same instruction set architecture (ISA). For some program, CPU A has a clock cycle time of 10 ns and a CPI of 2.0 CPU B has a clock cycle time of 20 ns and a CPI of 1.2 What machine is faster for this program, and by how much? seconds instructions Example cycles instruction seconds cycle constant program program trade-off . Percentage of instructions of a program (CPU A) compare 20%, branch 20%, others 60% compare 1 cycle, branch 2 cycles, others 1 cycle (CPI) - CPIA CPUAN . Percentage of instructions of the same program (CPU B) combine "compare & branch" in one instruction compare & branch 2 cycles, others 1 cycle (CPI) - CPIB = - CPUB=