Hit Rate

hit rate / hit ratio = the fraction of memory accesses found in the upper level

miss rate = (1−hit rate)

• the fraction of memory accesses not found in the upper level

Hit time = time to access the upper level of the memory hierarchy, which includes the time needed to determine whether the access is a hit or a miss

• With the library example, time to look through the books on your desk

miss penalty = time to replace a block in the upper level with the corresponding block from the lower level, plus the time to deliver this block to the processor