17.7 An earlier version of the IBM mainframe, the S/390 G4, used three levels of cache.As
with the z990, only the first level was on the processor chip [called the processor unit
(PU)]. The L2 cache was also similar to the z990. An L3 cache was on a separate chip
that acted as a memory controller, and was interposed between the L2 caches and the
memory cards. Table 17.4 shows the performance of a three-level cache arrangement
for the IBM S/390. The purpose of this problem is to determine whether the inclusion
of the third level of cache seems worthwhile. Determine the access penalty (average
number of PU cycles) for a system with only an L1 cache, and normalize that value to
1.0.Then determine the normalized access penalty when both an L1 and L2 cache are
used, and the access penalty when all three caches are used. Note the amount of
improvement in each case and state your opinion on the value of the L3 cache.