Investigating Sandy Bridge Memory Scaling

Intel's Second Generation Core processors, based on the Sandy Bridge architecture, include a number of improvements over the previous generation's Nehalem architecture. We’ll be testing one specific area today: the improved memory controller. Current Sandy Bridge based processors officially support up to DDR3-1333 memory. Unfortunately, due to changes in the architecture, using faster rated memory (or overclocking memory) on Sandy Bridge via raising the base clock is extremely limited. Luckily, there are additional memory multipliers that support DDR3-1600, DDR3-1866, and DDR3-2133 memory. Some motherboards include support for even higher memory multipliers, but we’ll confine our investigations to DDR3-2133 and below.

Since Sandy Bridge is rated for up to DDR3-1333 memory, we will start there and work our way up to DDR3-2133 memory. We'll also be testing a variety of common CAS latency options for these memory speeds. Our purpose is to show how higher bandwidth memory affects performance on Sandy Bridge, and how latency changes—or doesn’t change—the picture. More specifically, we’ll be looking at the impact of memory speed on application and gaming performance, with some synthetic memory tests thrown into the mix. We’ll also test some overclocked configurations. So how much difference will lowering the CAS latency make, and does memory performance scale with processor clock speed?

Back when I originally envisioned this comparison, the price gap between DDR3-1333 and DDR3-2133 memory was much wider. A quick scan of Newegg reveals that a mere $34 separates those two 4GB kits. Below is a breakdown of the lowest prices (as of 7/16/2011) for various memory configurations.

4GB 2x2GB Kits
DDR3-1333 CL9 $31
DDR3-1333 CL8 $40
DDR3-1600 CL9 $40
DDR3-1600 CL8 $41
DDR3-1333 CL7 $45
DDR3-1600 CL7 $50
DDR3-1866 CL9 $60
DDR3-2133 CL9 $65


8GB 2x4GB Kits
DDR3-1333 CL9 $58
DDR3-1600 CL9 $66
DDR3-1333 CL7 $75
DDR3-1600 CL8 $80
DDR3-1866 CL9 $85
DDR3-1600 CL7 $115
DDR3-2133 CL9 $150

You can see from the above chart that balancing memory clocks with latency results in some interesting choices, particularly on the 8GB kits where price differences are a bit larger. Is it best to go with a slower clock speed and better timings, or vice versa, or is the optimal path somewhere in between? That’s the aim of this article.

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  • vailr - Monday, July 25, 2011 - link

    No discussion of differing voltages?
    A quick check for DDR3 at Newegg shows:
    G.SKILL ECO Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600
    @ 1.35 volts & Cas Latency: 7
    vs.
    G.SKILL Ripjaws X Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600
    @ 1.50 volts & Cas Latency: 6
    A more thorough consideration of these two DDR3 modules might be interesting.
    For virtually the same money, aren't most people going to seek out DDR3 with the lowest possible CAS latency number, and also combined with the lowest possible voltage design?
    I know that: I wouldn't consider buying any DDR3 memory modules with a (nominal) CAS latency higher than 7.
    Reply
  • JarredWalton - Monday, July 25, 2011 - link

    Just as we didn't test with ten different modules (for ease of testing), we didn't use different voltage memory. Whether your RAM is 1.5V or 1.35V, at the same timings and speed the performance should be identical (less than a 0.5% difference). And we did look at the effect of lower latency RAM; sure, at the same price buy lower latency and higher bandwidth RAM, but prices aren't the same, particularly on 2x4GB kits. Reply
  • Tchamber - Monday, July 25, 2011 - link

    I'd like to see how these tests stack up against the tripple channel nehalem i7's. Reply
  • duploxxx - Monday, July 25, 2011 - link

    compare with what an EOL platform? it was alreay known that there is no added value with memory speed testing on these systems, just like the previous gen., 1366 is dead testing has been done in the past
    This test just showed that it is a lot of wasted money and time investigated in this.

    They better take the time and investigate further into Liano memory speed, something that really does scale with memory.
    Reply
  • Finally - Monday, July 25, 2011 - link

    It's already done, see Computerbase... Reply
  • JarredWalton - Monday, July 25, 2011 - link

    We've done it as well for graphics applications:
    http://www.anandtech.com/show/4476/amd-a83850-revi...

    We haven't done the application testing with different DDR3 on Llano, however.
    Reply
  • banwell - Monday, July 25, 2011 - link

    You can also get a nice 'free' bump in performance at 1600 by switching to 1T. Something the better quality memory will be able to do easily. Reply
  • AssBall - Monday, July 25, 2011 - link

    I'm not sure why they didn't test 1T . It is a memory scaling article after all. Anyway TechReport did and their conclusions are about the same, I.E. unless you are overclocking and running synthetic benchmarks, it doesn't really matter. Reply
  • compudaze - Monday, July 25, 2011 - link

    Lowering the command rate from 2T to 1T at DDR3-1600 doesn't necessarily mean you can do the same at DDR3-2133. Not all memory modules, CPU's and motherboards are creased equal. Testing all configurations at 2T kept the results comparable. Reply

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