11. Cache Organization, Operation, and Coherency
11.1 Memory Organization
Figure 11-1 shows the R4000 system memory hierarchy. In the logical memory hierarchy, caches lie between the CPU and main memory. They are designed to make the speedup of memory accesses transparent to the user. Each functional block in Figure 11-1 has the capacity to hold more data than the block above it. For instance, physical main memory has a larger capacity than the secondary cache. At the same time, each functional block takes longer to access than any block above it. For instance, it takes longer to access data in main memory than in the CPU on-chip registers.
Figure 11-1 Logical Hierarchy of Memory
The R4000 processor has two on-chip primary caches: one holds instructions (the instruction cache), the other holds data (the data cache). Off-chip, the R4000 processor supports a secondary cache on the R4000SC and MC models.
Copyright 1996, MIPS Technologies, Inc. -- 21 MAR 96
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