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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  • sprockkets - Monday, November 3, 2008 - link

    No, USB legacy support is for support during boot up and for the time you need input before an OS takes control of the system. However, as already mentioned, sometimes USB keyboards just don't work in a BIOS at startup for one reason or another, and in my opinion, this means they should NEVER get rid of the old PS/2 port.

    I ran into this problem with a Shuttle XPC with the G33 chipset, which had no ps/2 ports on it. There was a 50/50 chance it would not work.
    Reply
  • Clauzii - Thursday, November 6, 2008 - link

    I still use PS/2. None of the USB keyboards I've borrowed or tried out would work in 'boot'. Also I think a PS/2 keyboard/mouse don't lag so much, maybe because it has it's own non-shared interrupt line.

    But I can see a problem with PS/2 in the future, with keyboards like the Art Lebedev ones. When that technology gets more pocket friendly I'd gladly like to see upgraded but still dedicated keyboard/mouse connectors.
    Reply
  • The0ne - Monday, November 3, 2008 - link

    Yes. I have the PS2 keyboard on-hand in case my USB keyboard can't get in :) Reply
  • Strid - Monday, November 3, 2008 - link

    Ahh, makes sense. Thanks for clarifying! Reply
  • Genx87 - Monday, November 3, 2008 - link

    After living through the hell that were ATI drivers back in 2003-2004 on a 9600 Pro AIW. I didnt learn and I plopped money down on a 4850 and have had terrible driver quality since. More BSOD from the ati driver than I have had in windows in the past 5 years combined from anything. Back to Nvidia for me when I get a chance.

    That said this review is pretty much what I expected after reading the preview article in August. They are really trying to recapture market in the 4 socket space. A place where AMD has been able to do well. This chip is designed for server work. Ill pick one up after my E8400 runs out of steam.
    Reply
  • Griswold - Tuesday, November 4, 2008 - link

    You're just not clever enough to setup your system properly. I have two indentical systems sitting here side by side with the only difference being the video card (HD3870 in one and a 8800GT in the other) and the box with the nvidia cards gives me order of magnitude more headaches due to crashing driver. While that also happens on the 3870 machine now and then, its nowehere nearly as often. But the best part: none of the produces a BSOD. That is why I know you're most likely the culprit (the alternative is faulty hardware or a pathetic overclock). Reply
  • Lord 666 - Monday, November 3, 2008 - link

    The stock speed of a Q9550 is 2.83ghz, not 2.66qhz.

    Why the handicap?
    Reply
  • Anand Lal Shimpi - Monday, November 3, 2008 - link

    My mistake, it was a Q9450 that was used. The Q9550 label was from an earlier version of the spreadsheet that got canned due to time constraints. I wanted a clock-for-clock comparison with the i7-920 which runs at 2.66GHz.

    Take care,
    Anand
    Reply
  • faxon - Monday, November 3, 2008 - link

    toms hardware published an article detailing that there would be a cap on how high you are allowed to clock your part before it would downclock it back to stock. since this is an integrated par of the core, you can only turn it off/up/down if they unlock it. the limit was supposedly a 130watt thermal dissipation mark. what effect did this have in your tests on overclocking the 920? Reply
  • Gary Key - Monday, November 3, 2008 - link

    We have not had any problems clocking our 920 to the 3.6GHz~3.8GHz level with proper cooling. The 920, 940, and 965 will all clock down as core temps increase above the 80C level. We noticed half step decreases above 80C or so and watched our core multipliers throttle down to as low as 5.5 when core temps exceeded 90C and then increase back to normal as temperatures were lowered.

    This occurred with stock voltages or with the VCore set to 1.5V, it was dependent on thermals, not voltages or clock speeds in our tests. That said, I am still running a battery of tests on the 920 right now, but I have not seen an artificial cap yet. That does not mean it might not exist, just that we have not triggered it yet.

    I will try the 920 on the Intel board that Toms used this morning to see if it operates any differently than the ASUS and MSI boards.
    Reply

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