Intel's Warning on Memory Voltage

One of the most interesting changes for us with the release of the i7/X58 platform is the advances that have been made with DDR3. DDR3 had an auspicious introduction over a year and half ago when the P35 chipset debuted. Intel then introduced the X38 chipset with a focus on DDR3 support although DDR2 continued to perform better on the platform. It was not until the Intel X48 and NVIDIA 790i chipset releases earlier this year that users recognized DDR3 could become a performance factor on the desktop.

However, in order to glean the absolute best performance from these chipsets, the user needed DDR3 that was capable of running higher than DDR3-1800 speeds. The ICs from Micron at the time required a healthy 1.9V or higher to reach those speeds and the coveted 2000MHz mark. Samsung introduced a new family of ICs last spring that were capable of running up to 2200MHz or higher on +2.0V. While typical desktop applications or games did not take advantage of these speeds and resulting memory bandwidth, they did make for top results in the synthetic benchmarks.

Pricing was another problem that prevented the growth of DDR3 into the main stream market. Not only was DDR3 expensive, the market was flooded with DDR2 memory that performed equally well on the desktop at over half the price. As with most new technologies, it is a chicken and egg scenario when it comes to mass market product acceptance.

Intel had originally planned on X38/X48 being DDR3 only, but the market was not ready for it. We still feel that way to some degree but Intel believes this is the time for DDR3 to become their memory technology of choice for the next few years. As such, the introduction of i7/X58 brings with it a requirement for DDR3 memory. This requirement comes with a couple of caveats, the primary one being that Intel is highly recommending, more like suggesting a visit from the Grim Reaper is coming soon, that memory voltage does not exceed 1.65V on a long term basis or your new i7 might not work one day.

The majority of current DDR3-1066/1333 modules adhere to the base 1.5V JEDEC spec along with not needing more than 1.65V when overclocking, although overclocks amount to a couple hundred MHz increase at best with these products. The higher end DDR3 that has been on the market since last winter typically requires 1.8V or so to run above DDR3-1600. In fact, most of the current DDR3-1800+ memory usually requires 1.9V or higher. In some cases, depending on the SPD, it has difficulty even booting at 1.5V.

By coincidence or not, newer DDR3 ICs coming to market now from Qimonda, Samsung, and Elpida are able to operate from DDR3-1066 up to DDR3-1800 on 1.5V to 1.65V depending on timings and module size. In fact, we have experience with the new Samsung and Qimonda ICs (both 3GB and 6GB kits) operating at DDR3-1866 (9-9-8-20) up to DDR3-2000 (10-9-9-24) on 1.65V~1.75V with the ASUS Rampage II Extreme board. The good news is that these modules are starting to show up at the e-tailors with price points below previous DDR3 products.

This last week has been a busy one in the labs as we have started to receive a variety of memory modules from Kingston, OCZ, Patriot, GSkill, and Corsair for our upcoming DDR3 Shootout and Memory Guide for i7. The products range from the $109 3GB DDR3-1333 (9-9-9-24) kit from GSkill to the Corsair/OCZ 6GB DDR3-1600 (9-9-9-24) kits, and finally our DDR3-2000 (9-9-9-24) 1.65V kit from Kingston.

Our initial opinion at this time is that dual or tri-channel DDR3-1333 running at 8-8-8-20 timings will satisfy about 80% of the users in the market. In fact, DDR3-1066 at 7-7-7-18 might be the better solution for most applications right now considering the latency improvements over CAS8 or CAS9 DDR3-1333. Of course, running DDR3-1333 at CAS7 would be ideal from a price and performance viewpoint.

For the more performance oriented crowd, we have found the sweet spot for performance and keeping money in your wallet, to be tri-channel DDR3-1600 running at 8-8-8-20, something most of the new DDR3-1600 6GB kits will do easily on 1.6V or less. Of course, the benchmarking enthusiast will still want DDR3-1866 or higher on this platform. Something that is attainable now with voltages in the 1.65V~1.75V range depending on final speeds, board design, and loads as all three i7 processors are memory multiplier unlocked.

Getting back to that 1.65V warning, Intel is quite serious about this voltage level and is ensuring the board manufacturers remind the users in a variety of ways ranging from statements in the user manuals to various BIOS warnings when changing VDimm above 1.65V. We have been running exhaustive tests at various voltages and firmly believe that if VCore, QPI/IMC Voltage, and VDimm are properly aligned, that running VDimm up to 1.80V should be acceptable with proper cooling and non 24/7 operation. Of course that is not a promise, but we will have additional results shortly.

In the meantime, Intel also recommends not taking QPI/IMC (uncore/VTT) voltages above 1.3V. In fact, we think this setting is just as dangerous as or more so than high VDimm to the processor’s long term health. However, this setting is also one that greatly improves memory clocking and bclk levels along with a proper dose of IOH voltage. Just how far you can take QPI/IMC (VTT) voltage is something we are working on (1.475V is working well for us), just be aware that it is a delicate balance between this setting and VDimm to get the most out your memory. In most of our tests at this point on the 920, we usually bump QPI/IMC (VTT) voltage up to get additional memory/core clocks while maintaining the memory voltage around 1.65V.

What about the Impact of DDR3 Speeds? Thread It Like Its Hot
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  • anand4happy - Sunday, February 8, 2009 - link

    saw many thing but this is the thing something dfferent

    sd4us.blogspot.com/2009/01/intel-viivintel-975x-express-955x.html
    Reply
  • nidhoggr - Monday, November 10, 2008 - link

    I cant find that information on the test setup page. Reply
  • nidhoggr - Monday, November 10, 2008 - link

    test not text :) Reply
  • puffpio - Wednesday, November 5, 2008 - link

    would you guys consider rebenchmarking?
    from the x264 changelog since the nehalem specific optimizations:
    "Overall speed improvement with Nehalem vs Penryn at the same clock speed is around 40%."
    Reply
  • anartik - Wednesday, November 5, 2008 - link

    Good review and better than Tom's overall. However Tom's stumbled on something that changed my mind about gaming with Nehalem. While Anand's testing shows minimal performance gains (and came to the not good for games conclusion) Tom's approached it with 1-4 GPU's SLI or Crossfire. All I can say is the performance gains with Nvidia cards in SLI was stunning. Maybe the platform favors SLI or Nvidia had a driver advantage in licensing SLI to Intel. Either way Nehalem and SLI smoked ATI and the current 3.2 extreme quad across the board. Reply
  • dani31 - Wednesday, November 5, 2008 - link

    I know it would't change any conclusion, but since we discuss bleeding edge Intel hardware it would have been nice to see the same in the AMD testbed.

    Using a SB600 mobo (instead of the acclaimed SB750) and an old set of drivers makes it look like the AMD numbers were simply pasted from an old article.
    Reply
  • Casper42 - Tuesday, November 4, 2008 - link

    Something I think you guys missed in your article/conslusion is the fact that we're now able to pair a great CPU with a pretty damn good North/South Bridge AND SLI.

    I found that the 680/780/790 featureset is plainly lacking and that the Intel ICH9R/10R seems to always perform better and has more features. If any doubt, look at Matrix RAID vs nVidia's RAID. Night and day difference, especially with RAID5.

    The problem with the X38/X48 was you got a great board but were effectively locked into ATI for high end Gaming.

    Now we have the best of both worlds. You get ICH10R, a very well performing CPU (even the 920 beats most of the Intel Quad Core lineup) AND you can run 1/2/3 nVidia GPUs on the machine. In my opinion, this is a winning combination.


    The only downside I see is board designs seem to suck more and more.

    With socket 1366 being so massive and 6 DIMM slots on the Enthusiast/Gamer boards, we're seeing not only 6 expansion slots (down from the standard of 7) but in most boards I have seen pics of, the top slot is an x1 so they can wedge it next to the x58 IOH which means your left with only 5 slots for other cards. Using 3 dual slot cards is out of the question without a massive 10 slot case (of which there are only like 3-5 on the market) and even if you can wedge 2 or 3 dual slot cards into the machine, you have almost zero expansion card slots should you ever need them.

    Then we get to all the cooling crap surrounding the CPU. ALL these designs rely on a top down traditional cooler and if you decide to use a highly effective tower cooling solution, all the little heatsink fins on the Northbridge and pwer regulators around the CPU get very little or no airflow. Now your in there adding puny little 40/60mm fans that produce more noise than airflow, not to mention that the DIMMs are hardly ever cooled in today's board designs.
    Call me a cooling purist if you will, but I much prefer traditional front to back airflow and all this side intake top exhaust stuff just makes me cringe. I personally run a Tyan Thunder K8WE with 2 Hyper6+ coolers and the procs and RAM are all cooled front to back. Intake and exhaust are 120mm and I have a bit of an air channel in which that airflow never goes near the expansion card slots below, which by the way have a 92mm fan up front pushing air in across the drives and another 92mm fan clipped onto the expansion slots in the back pulling it back out.

    I dont know how to resolve these issues, but I think someone surely needs to because IMHO its getting out of control.
    Reply
  • lemonadesoda - Tuesday, November 4, 2008 - link

    "Looking at POV-Ray we see a 30% increase in performance for a 12% increase in total system power consumption, that more than exceeds Intel's 2:1 rule for performance improvement vs. increase in power consumption."

    You cant use "total system power", but must make the best estimate of CPU power draw. Why? Because imagine if you had a system with 6 sticks of RAM, 4 HDDs, etc. you would have ever increasing power figures that would make the ratio of increased power consumption (a/b) smaller and smaller!

    If you take your figures and subtract (a guestimate of) 100W for non CPU power draw, then you DONT get the Intel 2:1 ratio at all!

    The figures need revisiting.
    Reply
  • AnnonymousCoward - Thursday, November 6, 2008 - link

    Performance vs power appears to linearly increase with HT. Using the 100W figure for non-CPU draw means a 25% power increase, which is close to the 30% performance.

    Unless we're talking about servers, I think looking at power draw per application is silly. Just do idle power, load power, and maybe some kind of flops/watt benchmark just for fun.
    Reply
  • silversound - Tuesday, November 4, 2008 - link

    great article, tomsharware reviews always pro intel and nvidia, not sure if they got pay $ to suppot them. anandtech is always neutral, thx! Reply

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