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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  • Rick83 - Monday, July 25, 2011 - link

    Do they take into account, that we should be using 1.5V DIMMs for Sandy Bridge?

    The addition of that requirement usually limits choice quite a bit.
    Reply
  • compudaze - Monday, July 25, 2011 - link

    The SNB datasheet does suggest that the max memory voltage is 1.575V, however, many motherboard and memory manufactures state that they haven't had any problems with memory running at 1.65V on SNB. Reply
  • compudaze - Monday, July 25, 2011 - link

    Also, if you stick to the spec sheet, you shouldn't be running faster than DDR3-1333 memory. Reply
  • Taft12 - Monday, July 25, 2011 - link

    You should be using 1.5V DIMMs anyway - if a memory OEM needs 1.65V to achieve the same speed and timings another vendor does at 1.5V, it's inferior memory. Reply
  • jdogi - Monday, July 25, 2011 - link

    Just as your daily driver vehicle is likely inferior to a Mercedes or Ferrari. You should get a new car. You should not make any attempt to balance cost with the value. Just get the best. It's the only way to go. What's best for Taft is best for all.

    ;-)
    Reply
  • Iketh - Tuesday, July 26, 2011 - link

    you didn't understand the logic Reply
  • MrSpadge - Wednesday, July 27, 2011 - link

    I'm sure he did. What Taft failed to mention was that "at the same price, you should be using the memory spec'ed for less voltage". However, if some memory needs a little more voltage, but is way cheaper - balance cost and value.

    MrS
    Reply
  • Rick83 - Wednesday, July 27, 2011 - link

    Actually, the higher voltage is out of spec for the CPU memory controller and may wel impact longevity.
    So it's like buying the Ferrari, and running it on Biofuel with too much Ethanol that eats right through the tubing, but is marginally cheaper.
    Reply
  • jfelano - Tuesday, July 26, 2011 - link

    Not inferior, just older. All 1600mhz memory was 1.65v when it debuted. Then they came out with 1.5v, now even 1.35v. Reply
  • cervantesmx - Thursday, July 28, 2011 - link

    That is correct indeed. Just purchased 8GB at 1600mhz running on 1.25v. $59.99. Free shipping. Reply

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