42 the memory mountain the geography of the xeon

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Unformatted text preview: rite-allocate approach is that it is symmetric to the way reads are handled, in that write-back write-allocate tries to exploit locality. Thus, we can develop our programs at a high level to exhibit good spatial and temporal locality rather than trying to optimize for a particular memory system. 6.4.6 Instruction Caches and Unified Caches So far, we have assumed that caches hold only program data. But in fact, caches can hold instructions as well as data. A cache that holds instructions only is known as an i-cache. A cache that holds program data only is known as a d-cache. A cache that holds both instructions and data is known as a unified cache. A typical desktop systems includes an L1 i-cache and an L1 d-cache on the CPU chip itself, and a separate off-chip L2 unified cache. Figure 6.38 summarizes the basic setup. CPU Regs L1 d-cache L1 i-cache L2 Unified Cache Main Memory Disk Figure 6.38: A typical multi-level cache organization. 320 CHAPTER 6. THE MEMORY HIERARCHY Some higher-end systems, such as those based on the Alpha 21...
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This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.

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