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For reasons outlined in this chapter, modern microprocessor systems are moving in the following directions: |
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1. Split I- and D-caches. This ensures (especially for L/S processors) adequate cache-processor bandwidth. Some processors have implemented an I-cache only. This is probably not a good idea, since data access time to memory tends to dominate execution time. Except in extraordinary cases, some cache area should be allocated for both I and D functions. |
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2. The use of sectored caches. To optimize the area available for storing data, the sectored cache minimizes the directory size and affords an overall best marginal use of area. |
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3. Two-level cache, where the on-chip cache is supported by a larger, off-chip or even on-chip second-level cache. The two-level cache improves performance by effectively lowering the first-level cache access time and miss penalty. |
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