Memory Scaling with Overclocking

What happens when we increase the CPU clock speed on our Core i7-2600K from the default 3.5GHz to 4.8GHz; how will that affect memory performance? To find out, I ran the memory bandwidth tests again comparing DDR3-1333 CL9, DDR3-1600 CL9, and DDR3-2133 CL9 at both 3.5GHz and 4.8GHz CPU clock speeds. I also ran the most bandwidth intensive real-world test along with the least bandwidth intensive real-world test at the overclocked CPU speed to see if the faster CPU clock speed made any difference here as well.

AIDA64 v1.60.1300 - Memory Read (Overclocked)

AIDA64 v1.60.1300 - Memory Write (Overclocked)

AIDA64 v1.60.1300 - Memory Copy (Overclocked)

AIDA64 v1.60.1300 - Memory Latency (Overclocked)

The AIDA64 memory benchmark shows that memory bandwidth does scale with CPU clock speed. Going from DDR3-1333 to DDR3-1600 showed a 14% boost on our stock CPU while showing a 16% boost on our overclocked CPU. Stepping up from DDR3-1333 to DDR3-2133 saw a 33% increase on the stock CPU and a 43% increase on our overclocked CPU. The copy and latency tests showed similar results. What's more impressive is that the write test showed a much larger 15% increase from DDR3-1333 to DDR3-1600 on the overclocked CPU compared to 3% on the stock CPU. Going from DDR3-1333 to DDR3-2133 increased write performance by 22% when overclocked compared to 7% when stock. While it's interesting to see how an overclocked CPU affects raw memory bandwidth, I'm much more interested to see how it affects our real-world benchmarks.

x264 HD Benchmark v4.0 - Pass 1 (Overclocked)

x264 HD Benchmark v4.0 - Pass 2  (Overclocked)

Cinebench R11.5 - CPU (Overclocked)

The extra bandwidth gained with the overclocked CPU doesn't exactly translate into much. The first pass of the x264 test reveals a 7% advantage for DDR3-2133 over DDR3-1333 on our overclocked CPU while the stock CPU shows a 5% increase. The increase for DDR3-1600 over DDR3-1333 is 3% for both our overclocked and stock CPUs. Once we move on to the second pass, there's no discernible advantage for faster memory on our overclocked system. The Cinebench test results are every bit as unimpressive with overclocking as at stock: overclocked or not, faster memory makes no real difference (though the faster CPU clock speed definitely helps a lot).

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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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