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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  • tomx78 - Tuesday, July 26, 2011 - link

    Article is called "choosing the best DDR3" so I agree they should test T1. Without it whole article is useless. It still does not answer question which DDR3 is best. If DDR3-2133 can't do T1 but DDR3-1600 can which one is faster? Reply
  • Impulses - Monday, July 25, 2011 - link

    If you're pinching pennies and trying to build a system on a budget, even the $10 premium for anything but a basic 1333 kit doesn't seem worthwhile... I actually chose my last 2x4GB kit based on price and looks more than anything, heh, the old G.skill Sniper heatspreaders (the blue-ish version) matched my MSI mobo well and looked like they'd be the least likely to interfere with any heatsink. Some of the heatspreaders on pricier kits are crazy big, not to mention kinda gaudy. Reply
  • Finally - Tuesday, July 26, 2011 - link

    Let me repeat: You buy your RAM based on... aesthetics?
    No further questions, thanks.
    Reply
  • Finraziel - Wednesday, July 27, 2011 - link

    Well as this test showed, there is little performance gain to be had, so what else is there to base your choice on? Especially for people with windows it can be important. And if you buy really fast memory that wont fit under your heatsink, well, let's just say you want to insinuate someone else is dumb? :)
    I used to have the Corsair modules with lights on top showing activity, and while I mainly bought them for looks, they were actually useful at times to be able to quickly check if my system had totally crashed or was still doing stuff (you can sort of see the difference in the patterns in the lights).
    Reply
  • knedle - Monday, July 25, 2011 - link

    I would love to see graphs showing how much power do different ram modules consume, few weaks ago I build low power computer with Sandy Bridge and I'm still looking into how to get as much from it as possible, with as low power consumption as possible. Reply
  • Rajinder Gill - Monday, July 25, 2011 - link

    Power savings for DRAM are generally small. As you lower the current draw (either by reducing voltage or slacker timings) you are battling in part against the efficiency curve of the VRM.

    On some boards the difference in power consumption between DDR3-1333 and DDR3-1866 (given voltage and timing changes) can be as little as 1 Watt.

    -Raja
    Reply
  • Vhozard - Monday, July 25, 2011 - link

    "Multiple passes are generally used to ensure the highest quality video output, and the first pass tends to be more I/O bound while the second pass is typically constrained by CPU performance."

    This is really not true, multiple passes are used by x264 to come as close as possible to a given file size. A one-pass crf-based encode produces an equally high quality video output, given the same conditions.

    Maybe you should use one-pass encodes, as they are more commonly used when file size specification is not very important.
    Reply
  • JarredWalton - Monday, July 25, 2011 - link

    Multiple passes produce higher quality by using a higher bitrate where it's needed and a lower bitrate where it's not. In a single-pass, constant bitrate encode, scenes where there's a lot of movement will show more compression artifacts. There's no need to do multiple passes for size considerations: you do a constant bitrate of 2.0Mbps (including audio) for 120 minutes and you will end up with a file size of very close to 1800MB (or if you prefer, 1717.61MiB). Variable bitrate with a single pass doesn't have an accurate file size. Reply
  • Vhozard - Monday, July 25, 2011 - link

    Very few people still use constant bitrate encodes.
    x264 works with a crf (constant rate factor), which gives constant *quality*; not constant bitrate!

    There is very much a need to do multiple passes for size considerations as a constant bitrate will not give them optimal quality at all.

    The quality between a crf (one-pass) of 15 that reaches a filesize of lets say 1 GBwill have almost exactly the same quality as a two-pass which is set at 1 GB.

    I suggest you read the x264 wiki...
    Reply
  • JarredWalton - Monday, July 25, 2011 - link

    Sorry -- missed that you said CRF and not CBF. Reply

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