Articles: Memory

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Clock Rate’s Effect on Performance

Now we’ve reached the main part of this review. We are going to find out how memory subsystem parameters can affect the overall performance of a computer in everyday applications. Considering what we've said in the previous section, we won't benchmark memory subsystems with different timings. Instead, we will focus on investigating the performance-frequency correlation. So we've taken popular memory configurations with clock rates from 1333 to 2667 MHz and selected typical timings for them. So, we ended up having the following DDr3 SDRAM types participate in our test session:

  • DDR3-1333 9-9-9-27-1N;
  • DDR3-1600 9-9-9-27-1N;
  • DDR3-1867 9-9-9-27-1N;
  • DDR3-2133 11-11-11-33-1N;
  • DDR3-2400 11-11-11-33-1N;
  • DDR3-2667 11-13-13-35-1N.

Otherwise, our testbed with a quad-core Core i5-3570K (Ivy Bridge) overclocked to 4.5 GHz was unchanged.

Synthetic benchmarks come first.

A higher clock rate expectedly helps to increase the effective bandwidth and reduce the effective latency of DDR3 SDRAM. Interestingly, we can see the largest increase in memory speed when the clock rate grows up to 2133 MHz. After that, the high clock rate doesn't have such a high effect. We can also note that switching to 1600 MHz has the biggest effect, indicating that DDR3-1333 looks like an outdated solution now. Overall, the 100% increase in frequency, from 1333 to 2666 MHz, leads to an up to 50% increase in effective bandwidth and latency.

The memory subsystem benchmark from Aida64 is single-threaded, so it doesn’t reveal the full potential of today’s memory controllers. Therefore we additionally ran the Stream benchmark in quad-threaded mode (to match the number of CPU cores in our testbed).

Indeed, the correlation between the memory subsystem’s bandwidth and clock rate is outlined sharper here than in Aida64. Switching from 2133 to 2400 MHz produces a noticeable effect, but the next 266MHz step doesn't seem so useful. Overall, when we progress from DDR3-1333 to DDR3-2400 or DDR3-2666, we can enjoy a 64% increase in data processing speed.

Well, these synthetic benchmarks can only draw some ideal picture but can hardly give us a notion of how the memory subsystem is going to behave in real-life applications. Let’s check them out, too.

Futuremark's benchmarks are not as enthusiastic as the synthetic ones: the clock rate does affect system performance but not that much. Increasing the clock rate by 266 MHz raises the overall score in PCMark 7 and 3DMark 11 by less than 1 percent, the physics test of the graphics benchmark being the only one to show some susceptibility to memory subsystem settings. That test runs up to 14% faster with overclocked DDR3 SDRAM.

It is in WinRAR that we can observe the biggest performance benefits from higher memory clock rates. In the rest of the applications fast DDR3 SDRAM can only speed the computer up by just a few percent.

We must admit that gaming applications differ somewhat in this respect. Memory subsystem performance has a larger effect on them. By preferring high-bandwidth DDR3 SDRAM for your Ivy Bridge platform, you can get an additional 5-10% in terms of frame rate. You don’t always achieve this even by installing a faster CPU!

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