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DRAM Almost as Fast as SRAM
An anonymous reader writes "IBM said it has been able to speed up the DRAM to the point where it's nearly as fast as SRAM, and that the result is a type of memory known as embedded DRAM, or eDRAM, that helps boost the performance of chips with multiple core calculating engines and is particularly suited for enabling the movement of graphics in gaming and other multimedia applications. DRAM will also continue to be used off the chip."
There are 2 areas of latency for a cache, the first is the performance of the actual data cells, and the second is the speed of doing a lookup in the cache. The larger the cache, and the higher the degree of set associativity, the longer the lookup takes. Thus you're unlikely to see this eDRAM used for L1 caches, and probably not for L2 caches either, as more cache would slow them down, even if the cells are just as fast as SRAM. The sweet spot will probably be for L3 caches, that are already slow by cache standards, but a whole lot faster than system memory. Since L3 caches are large, the cost savings for switching to eDRAM would be largest there.
As for power concerns, DRAM is higher than SRAM, but a larger L3 cache may reduce the traffic through the memory controller, and out to the DIMMs, which will probably more than make up for any increase in power density in the cache.