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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  • Kevin G - Monday, July 25, 2011 - link

    One thing worth noting is that the memory controller has to run at least twice the clock speed of the memory (ie, the memory controller runs at 3.2 Ghz for 1600 Mhz DDR3 rated memory). This is one of the reasons why Intel doesn't officially support memory speed higher than 1600 Mhz. Running the CPU cores and memory controller at the same clock speed should produce a benefit even if memory speed isn't improved (ie running the CPU and memory controller at 4.8 Ghz with 1600 Mhz memory). It would be interesting to see how just scaling the memory controller's speed affected performance.

    I wish that their were a few game tests utilizing the integrated GPU. For a desktop, using a discrete graphics card for gaming is a new brainer over Intel's integrated graphics. However many laptops will only use Intel's solution and thus improving memory performance could be a means of improving gaming performance here. Further more, laptops are often lower resolution than 1920 x 1080 and thus the performance delta between memory speeds would be wider.
    Reply
  • RussianSensation - Monday, July 25, 2011 - link

    But even if laptops run at lower resolutions, they have much weaker CPUs and GPUs and generally have slow 5400 rpm hard drives. So if anything, memory speed will be even less important in a laptop since a laptop will be faced with all kinds if I/O, GPU and CPU bottlenecks.

    Improving performance of Intel's gaming solution with faster memory is a waste of time. HD3000 is just a dog. If you want a budget gaming laptop, you get Llano. No amount of memory bandwidth is going to translate into a more playable gaming experience on the HD3000.
    Reply
  • Kevin G - Monday, July 25, 2011 - link

    Except that Llano is in the same situation as it too needs fast memory for better graphics performance. If DIMM manufacturers start rolling out high performance memory for Llano, Sandy bridge laptops can also benefit. So why not actually test to see what those benefits could be? Reply
  • orenlevy - Tuesday, July 26, 2011 - link

    there is defenetly gpu improvment on hd3000 i dont know why you are not benching on Z68 platform. personally i have z68 htpc and sure i noticed different lateness on normal use. we always like sppedy windows poping and that simply whats happans.
    personally i say to myself "oh its about time to squeez little bit more from the sandybridge" even the G840 behave so different on 1600M cl8 Z68...
    Reply
  • jabber - Monday, July 25, 2011 - link

    As its such a waste of life. RAM hasnt been fun or that important since the good old DDR days.

    They may as well just hardwire 4GB of bog standard ram onto the motherboard for most folks.
    Reply
  • silverblue - Monday, July 25, 2011 - link

    Maybe they have, but RAM speed is important for iGPUs and especially so for APUs.

    For those wondering where the Llano equivalent is...

    http://www.anandtech.com/show/4476/amd-a83850-revi...
    Reply
  • silverblue - Monday, July 25, 2011 - link

    Duh. The link is on the final page of this article. Reply
  • Kevin G - Monday, July 25, 2011 - link

    The main reason why RAM still comes on DIMMs is due to reliability and the need for expansion. Cost is also a factor, especially for motherboards with lot of RAM soldered on to it.

    However, soldering down RAM in some situations does make sense. Expandability in laptops for example. Another area where soldiered RAM on a desktop motherboard would make sense is with the overclocking crowd. The RAM could be placed closer to the CPU socket which could easily increase clock speeds. The elimination of the edge connector on the DIMM would also significantly enhance signal strength too. Physical placement on the motherboard would allow for better cooling (larger heat sinks or water cooling with direct contract with the RAM chips). There would also be room for robust power delivery to the RAM chips on the motherboard.
    Reply
  • dac7nco - Monday, July 25, 2011 - link

    I' glad there are still RAM reviews; 1.5v DDR3 1600 / CAS 7/7/7 gets me an additional 1 to 2 FPS in long Handbrake transcodes, which is a big part of my bread and butter.

    Keep in mind, 1.5v, no higher, is the DDR3 spec, which is why you'll never see ECC DDR3 registered memory rated above that. Keep this in mind, Anand: Control your people! X58-rated memory has no place today.

    Daimon
    Reply
  • jabber - Monday, July 25, 2011 - link

    I still think the main selling pint for RAM is - How well does it match my motherboard?

    Maybe a round up of modules with fancy spreaders and how they look in Asus/Gigabyte/Asrock/MSI boards.
    Reply

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