Issue No. 07 - July (1998 vol. 31)
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/2.689677
Memory speeds have not kept up with processor speeds. More precisely, DRAM latency has not kept pace: Processor speeds have been increasing by at least 70 percent per year, while DRAM latency has improved only 7 percent annually. As a result, a contemporary superscalar 300-MHz DEC Alpha system with a 40-ns DRAM can perform at least 24 instructions in the time it takes to access its memory just once. In a few years, if current trends continue, the number of instructions per access could increase to a thousand. Fortunately, memory bandwidth is another matter. Wider buses, multiple banks, more pins, the integrated circuit properties of DRAMs (such as static-column mode and on-chip cache), and the newer Rambus and synchronous DRAM have all contributed to band-widths that have scaled better than latency. A central problem for memory system designers is how to exploit this bandwidth to achieve lower latencies. In this article, we describe a technique that can convert more than 90 percent of a memory system's bandwidth into low-latency accesses, at least for a particular class of computations. The scheme nicely complements traditional caching in two ways: It handles frequently occurring memory reference patterns for which caches do not perform well and-by removing this problematic data from the cache-it reduces pollution, making the cache more effective for the remaining references.
R. H. Klenke et al., "Smarter Memory: Improving Bandwidth for Streamed References," in Computer, vol. 31, no. , pp. 54-63, 1998.