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8 GB Article and Phenom II memory compatibility


MikeCG

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I've seen similar questions asked, but I don't think I've seen this particular angle being addressed. One instance, all I saw as a reply was essentially, "Great find." But no confirming of the setup or anything (maybe it was, but I must have overlooked?). I mean, it is one of your articles, after all, so I guess it's reliable, but I've also seen it repeated ad nauseum here about how AMD chips can't handle more than 1333MHz, and only with two modules, and here's one of your people using a pair of 1600MHz 4GB kits together (a total of four modules/slots used) to show just how much of a gain comes from having twice as much ram. Now, admittedly, the module kits are of a new product of yours that's only being distributed in limited quantities so far, and maybe this kit makes the difference..? But then why the 1600MHz kits that are already marketed as AMD/Black Edition-ready, available most everywhere? If AMD's chips, presumably even the new C3 stepping, can't handle more than 1333MHz, as I see repeated so often here, then why bother marketing memory for a speed that is, therefore, beyond the chips' ability, according to official responses given here on the forums?

 

In any case, I have been looking around at 1600MHz Corsair kits and 790FX chipset motherboards, specifically the Asus M4A79T Deluxe and the Crosshair III. The QVLs for these motherboards are a bit out of date, but the M4A79T Deluxe has a far more recent QVL that actually lists two 1600MHz C7 Corsair kits, and I don't even think they're Dominators. They have DHX-based suffixes. DHXIN, to be specific. But I don't think you market memory with those kinds of designations anymore. Even the newer Dominators no longer have the 'D's at the end. Though it looks like it's been moved to the start of the part number, now. CMD for Corsair Memory Dominator, I suppose...

 

Moving on... I also observed, at least with the older Crosshair III QVL (until they give an up-to-date QVL, their 6-7 month old list will have to do) that a competitor's memory was listed as having managed the listed specs of 1600 C7, though admittedly it was a 2x1GB kit, so I guess the density was a factor..?

 

Another thing... the CPU from the 8GB Article was a Phenom II X3 710... do only Heka chips have this capability of handling high speed, low latency, high capacity memory? Or is this, as I postulated earlier, a result of better-tuned memory? According to my research, the 710 is also a C2, so presumably the stepping isn't the factor. The motherboard could be a factor, though, but I really have an aversion to a brand with such a name as 'Gigabyte'... Just seems tacky, and suggests prone to obsolescence since it's stuck to a form of measurement whose limits grow exponentially, as is the case with anything related to computers (are they going to change their name to Terabyte eventually?).

 

So any clarity to be had on all this? Sorry if I got too long-winded, but I did have a lot on my mind...

 

EDIT: Oh, I also thought to comment that it's rather strange that the Crosshair is billed as a 'gaming motherboard' with its 'Republic of Gamers' branding and so forth, but the QVL only shows that, at least based on the possibly out-of-date information, it rarely handles better RAM settings than the more 'mainstream' marketed variant with the same chipsets, the aforementioned M4A79T Deluxe. Maybe if Asus bothered to put out another, more complete QVL for the Crosshair III that shows it holds its own against it's nearly-identical non-ROG variant in terms of RAM settings, it wouldn't seem so poor a motherboard. But maybe, in the end, it really isn't worth the branding and marketing, and that's the point. Though Asus is also putting out a new version of the M4A79T Deluxe that uses the third-generation SATA and USB technologies, so maybe that will be the preferred board from them, or it may be a sign that they will do the same with the Crosshair line..? Or will they wait until AMD 8-series chipsets...

 

Sorry if I'm a bit too inquisitive and/or random. I'm very interested in the industry and understanding the new technologies so I'm well-informed for assembling systems, and DDR3 on AMD seems to be rather murky, and what works and what doesn't is rather fluid so far. With DDR2, 1066MHz was a sure bet when I was assembling systems, and I always got Corsair. I'd like to continue getting Corsair, as I've done well by them. Who knows, though. Perhaps by the time I do assemble DDR3 AMD systems, there will be more certainty in the capabilities. Or perhaps there is and I'm just not seeing it yet and someone will help me see that here..? I tried looking up the Corsair 1600MHz C7 modules on the compatibility configurator, and found absolutely nothing, which wasn't very encouraging for the ideas I've been entertaining.

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The main thing that running 8GB at 1600MHz is going to be the memory controller on the actual CPU. Not all CPUs can do it however most will need to be slowed to a slower speed. Tweaking various sub timings on various boards also seem to help stability as well.
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The main thing that running 8GB at 1600MHz is going to be the memory controller on the actual CPU. Not all CPUs can do it however most will need to be slowed to a slower speed. Tweaking various sub timings on various boards also seem to help stability as well.

 

Yes, your mileage may vary if running memory at DDR3-1600 speed. The official JEDEC standards for DDR3 memory recommend only two ranks per channel at that speed. At DDR3-1333 speed or lower, JEDEC recommends up to four ranks of memory per channel. And at present all 2GB and larger memory modules are double-ranked or "quad-ranked" (two or four ranks per module). Officially, quad-ranked memory modules cannot be legitimately sold with speed ratings higher than DDR3-1333.

 

What's more, DDR3-1600 speed is considered officially out of spec for an AMD processor. The AMD memory controller in DDR3 mode officially supports only two ranks of memory per channel at DDR3-1333 speed. If you're going to run four ranks of DDR3 memory per channel (two double-ranked modules in each pair of slots) on an AMD platform, DDR3-1066 is advised for better stability. And all that is due to the idiosyncratic divider setup in the AMD memory controller setup - the actual memory clock speed is a set fraction of the CPU's core clock speed; for example, with the memory speed set at DDR3-1333, a 3.0 GHz AMD processor actually runs that memory at only DDR3-1200 speed. Or a 2.8 GHz AMD processor can only run DDR3-1066 memory at DDR3-933 speed (with the next higher available setting being DDR3-1120, which is higher than the official DDR3-1066 spec but is exactly what the next-higher JEDEC-standard memory speed, DDR3-1333, would have defaulted to with that particular 2.8 GHz CPU anyway)! The AMD divider setup worked well at a time when memory clock speeds were far lower than the CPU core speeds (and thus at very or extremely high divider ratios). But with actual memory I/O clock speeds getting dangerously close to the CPU core clock speeds, the divider ratios become so ridiculously low that at certain CPU clock speeds there would have been no advantage at all whatsoever running DDR3-1600 memory instead of DDR3-1333 memory (this point comes at a CPU core clock speed of 2.6 GHz, where both DDR3-1333 and DDR3-1600 memory would have run at the exact same speed of DDR3-1300, and the next higher internal memory controller setting after DDR3-1300 would have been an out-of-spec DDR3-1733). There is no current upper-consumer-level processor with an on-die memory controller - Intel or AMD - which officially supports DDR3-1600 at all in spite of that speed being part of the official JEDEC spec. (The Core i7 Extreme might officially support DDR3-1600, but it is priced way too high for most consumers.)

 

And unlike the Intel i-series processors (which all require DDR3 memory), the AMD Phenom II processors can use DDR3 memory if installed on an AM3 motherboard or DDR2 memory if installed on an AM2 or AM2+ motherboard (the on-die memory controller supports either type of memory). A BIOS update may be required in order to use Phenom II processors on existing DDR2 motherboards. But because Socket AM3 actually has fewer pins than its AM2 predecessor (938 pins versus 940), existing AM2(+) processors will not even physically fit the Socket AM3 receptacle but the newer AM3 processors will fit existing AM2 sockets.

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