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Effect of Memory Timings and Frequency on Performance

In the meantime we got to the most exciting part of our today’s discussion: finding out what is more important for the memory sub-system in the new LGA 2011 platform – low timings or high frequency. This question is inevitable upon the launch of every new platform, and this time is also no exception. All previous Intel platforms with DDR3 SDRAM favored the increase in memory frequency more than lowering of its timings, but things are different with Sandy Bridge-E. This CPU uses quad-channel memory, which by itself provides superior bandwidth and additional increase in the frequency of the DDR3 SDRAM modules may turn out unnecessary. Therefore, we were particularly excited about this part of our test session.

We started with synthetic benchmarks.

Higher operation frequency of DDR3 SDRAM allows increasing its practical bandwidth and lowering practical latencies. Lower timings produce a similar effect, but according to AIDA64 cache & Memory Benchmark, this effect is significantly smaller than after frequency overclocking.

However, as we have already found out earlier, AIDA benchmark doesn’t measure the characteristics of Sandy Bridge-E memory controller correctly. Therefore, we also ran the tests in Stream benchmark in two modes – with one and eight threads:

This new test only confirms everything that we have just said. Practical memory bandwidth continues to grow as its frequency increases, and the gain in this case exceeds the effect from lowering the memory timings. So, it looks like we won’t be able to uncover any new connections between the performance and the parameters of the memory sub-system in the LGA 2011 platform.

And here are the results of a few benchmarks measuring complex system performance:

The frequency of DDR3 modules is a more important parameter for the system performance than its latencies in the end of the day. Now we have every reason to state this with all certainty. And 1.5 times better timings (as we can see from the DDR3-1333 example) only improved the performance by 1.6%, while increase in memory frequency by one 266 MHz increment delivered a 1.9% average performance boost. However, both these numbers are rather modest, which indicates that memory sub-system settings have very small overall effect on the system performance. Even a seemingly significant upgrade from quad-channel DDr3-1333 to quad-channel DDR3-2133 improves the performance by only 4% on average. Of course, there are applications that could benefit much more from having faster memory, but eve a memory-sensitive WinRAR archiving tool will speed up by only 19% after an 80% increase in memory frequency.

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