Cold-Start vs. Warm-Start Miss Ratios In a two-level computer storage hierarchy, miss ratio measurements are often made from a "cold start," that is made with the first-level store initially empty. For large capacities the effect on the measured miss ratio of the misses incurred while filling the first-level store can be significant, even for long reference strings. Use of "warm-start" rather than "cold-start" miss ratios cast doubt on the widespread belief that the observed "S-shape" of lifetime (reciprocal of miss ratio) versus capacity curve indicates a property of behavior of programs that maintain a constant number of pages in main storage. On the other hand, if cold-start miss ratios are measured as a function of capacity and measurement length, then they are useful in studying systems in which operation of a program is periodically interrupted by task switches. It is shown how to obtain, under simple assumptions, the cache miss ratio for multiprogramming from cold-start miss ratio values and how to obtain approximate cold-start miss ratios from warm-start miss ratios. CACM October, 1978 Easton, M. Fagin, R. Miss ratio, cold start, warm start, storage hierarchy, lifetime function, multiprogramming, S-shape 3.70 4.32 9.35 CA781009 DH January 29, 1979 5:16 PM 2374 4 3052 2481 4 3052 2669 4 3052 2863 4 3052 3016 4 3052 3052 4 3052 1901 5 3052 3052 5 3052 3052 5 3052 3052 5 3052