This preview shows page 1. Sign up to view the full content.
Unformatted text preview: in the memory hierarchy has a big impact on the way that it is organized. Recall that a DRAM is about 10 times slower than an SRAM and that disk is about 100,000 times slower than a DRAM. Thus, misses in DRAM caches are very expensive compared to misses in SRAM caches because DRAM cache misses are served from disk, while SRAM cache misses are usually served from DRAM-based main memory. Further, the cost of reading the ﬁrst byte from a disk sector is about 100,000 times slower than reading successive bytes in the sector. The bottom line is that the organization of the DRAM cache is driven entirely by the enormous cost of misses. Because of the large miss penalty and the expense of accessing the ﬁrst byte, virtual pages tend to be large, typically four to eight KB. Due to the large miss penalty, DRAM caches are fully associative, that is, any virtual page can be placed in any physical page. The replacement policy on misses also assumes greater importance, because the penalty associat...
View Full Document
- Spring '10
- The American