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DDR speed limitations/CPU?

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a c 131 à CPUs
July 23, 2010 7:48:03 PM

Ok, this has been bugging me for a while. What exactly does the MHz of ram that a CPU supports mean? I mean, obviously you can overclock the ram.
Is it simpler than I think? Is it that the CPU will run any faster ram at it's own spec speed unless overclocked? ie, the Athlon IIx4 would run DDR3 1333 at 1066MHz?

Another question, is if my assumption is correct, then why are high end CPUs currently limited to 1333MHz ram? Is there some kind of technological limitation that needed to be worked out that I am missing here?

Thanks in advance :whistle: 
a c 83 à CPUs
July 23, 2010 9:36:23 PM

I can't say for sure, but I believe it's memory controller limitations. I've seen a few cases where Phenom II X4 was unstable running DDR3 1600 and was forced to run at 1333 speeds, but most of the time 1600 works fine. My guess is the low speed ratings is so AMD doesn't have to junk good processors just because the memory controller is a little weaker.
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a b à CPUs
July 23, 2010 9:45:51 PM

the max memory speed is from the memory controller which right now for both Intel and AMD is inside the cpu, and i would imagine that loneninja is probably right about why

though from what it seems most of these memory controllers are fine and can run at much higher speeds than they are rated, thoguh it is possible to get one that can only run at the advertised speed
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a b à CPUs
July 23, 2010 9:50:05 PM

Do you mean like the core i7 officially which only supports DDR3 up to 1066MHZ?

If so, it's just the maximum supported speed by Intel. It's the speed they give up at which they give a 100% garantee that their cpu will work flawlessly. Of couse it can run at much higher speeds to above 2000MHz, but then stability chances may be 99.9% instead of 100%. Who cares anyway?

Don't worry about it. I think it has more to do with Intel protecting itself from being blamed building instable platforms that might crash in one occasion out of 10000 if they would set the max supported speed at 1600mhz.

However, I have to say that some motherboards get into trouble and do not post when the ram is set above 1066mhz, but mostly it gets solved by a bios update.

Once again, don't worry about it. If you want to buy a system with faster ram than supported, read as many reviews about the board until you're sure it can handle it or post a question on a forum like this. That's what I did when I bought my core i7 rig with 1600mhz ram.
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a c 131 à CPUs
July 24, 2010 12:15:32 AM

^lol. I never mentioned intel. Nor did I say I was planning to buy an i7. Can someone on this forum not be curious about something while at the same time not intending to purchase a new computer :p 

Part of my question has been answered so far and some good answers. Just one part that's been left alone is "Is it that the CPU will run any faster ram at it's own spec speed unless overclocked? ie, the Athlon IIx4 would run DDR3 1333 at 1066MHz? ". Since I don't own a system with DDR3 memory and my ram is default 800MHz, I can't investigate this myself.
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a c 83 à CPUs
July 24, 2010 3:12:48 AM

Sorry, can't answer that last part either, I'm still on AM2+ systems. DDR2 1066 is the fastest thing I have.
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a b à CPUs
July 25, 2010 1:41:35 PM

enzo matrix said:
^lol. I never mentioned intel. Nor did I say I was planning to buy an i7. Can someone on this forum not be curious about something while at the same time not intending to purchase a new computer :p 

Part of my question has been answered so far and some good answers. Just one part that's been left alone is "Is it that the CPU will run any faster ram at it's own spec speed unless overclocked? ie, the Athlon IIx4 would run DDR3 1333 at 1066MHz? ". Since I don't own a system with DDR3 memory and my ram is default 800MHz, I can't investigate this myself.

I wasn't trying to convince you buying an i7 system at all. I just mentioned it as an example because I have more experience with i7 than any AMD system.

To answer the second part of your question. Ram speed has nothing to do with CPU speed at all. Both can be under/overclocked independently. For example with Intel systems, both have their own multipliers, linking them to one general clock, namely the FSB for older systems or the Baseclock for i-x systems.

To conclude, you can run any ram on any cpu, however you'll have to make sure your mobo supports both speed and type of ram. To do that, read reviews. You won't have to OC the CPU to be able to clock the ram at higher speed, unless there's some kind of technical limit, like not having a high enough ram MP, to get the desired ram speed at the current general clock, however that's not likely. Even then you can still up the general clock and lower the cpu mp to keep it at the same speed. It's all a little bit like puzzling.

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a c 131 à CPUs
July 25, 2010 3:43:52 PM

Nils said:
To answer the second part of your question. Ram speed has nothing to do with CPU speed at all. Both can be under/overclocked independently. For example with Intel systems, both have their own multipliers, linking them to one general clock, namely the FSB for older systems or the Baseclock for i-x systems.

I am well aware of this, and this is not my second question. When I said "own spec speed" I meant, for example, would an Athlon II run 1600MHz ram at 1066MHz (it's spec) unless the base clock is overclocked?
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a b à CPUs
July 25, 2010 9:06:02 PM

enzo matrix said:
I am well aware of this, and this is not my second question. When I said "own spec speed" I meant, for example, would an Athlon II run 1600MHz ram at 1066MHz (it's spec) unless the base clock is overclocked?

Sorry, misunderstood you.

Oh no, that will not be possible I think, unless you have worldclass overclocking ram ;) 
If the ram states 1066Mhz, then that will be it's maximum speed, apart from it's OC'ing capabilities. That's what the chips are made for. However, it's not because Intel or AMD says their chipsets support a maximum ram speed of x mhz, that ram companies won't make faster ram.

If you want to run your ram at 1600 Mhz, you'll have to buy a kit that states 1600Mhz.

The opposite however seems to exist. In my case I wanted 1600mhz so I bought a kit of 1600mhz ram. Once installed I ran cpu-z and there I saw the highest JEDEC profile was 1333 and the 1600mhz profile was xmp. And officially only JEDEC profiles matter, so officially my ram is 1333mhz. However, ram companies know that some chip-productionlines (not all) can run at higher speeds, so they use XMP profiles to program higher speeds and then they are stated as overclock speeds, even though they know the chips are more that stable then.
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a c 131 à CPUs
July 26, 2010 6:30:34 AM

Nils said:
Sorry, misunderstood you.

Oh no, that will not be possible I think, unless you have worldclass overclocking ram ;) 
If the ram states 1066Mhz, then that will be it's maximum speed, apart from it's OC'ing capabilities. That's what the chips are made for. However, it's not because Intel or AMD says their chipsets support a maximum ram speed of x mhz, that ram companies won't make faster ram.

If you want to run your ram at 1600 Mhz, you'll have to buy a kit that states 1600Mhz.

lol.. You misunderstand again. I said "it's spec" I was talking about the speed the CPU is specced to run the ram at. For example, the Athlon IIx4 only supports up to 1066MHz. If I were to put 1600MHz in that system, would it run at 1066MHz by default because of this or would it be run at 1600MHz?
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a b à CPUs
July 26, 2010 2:56:14 PM

enzo matrix said:
lol.. You misunderstand again. I said "it's spec" I was talking about the speed the CPU is specced to run the ram at. For example, the Athlon IIx4 only supports up to 1066MHz. If I were to put 1600MHz in that system, would it run at 1066MHz by default because of this or would it be run at 1600MHz?


if the spec of the cpu is 1066 it will run at 1066, though most motherboards i have seen have the multipliers to get 1600 without changing the base clock (and apparently the cpu has the multi as well), they just don't guarantee the cpu's IMC to run at those speeds
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a b à CPUs
July 26, 2010 3:36:38 PM

enzo matrix said:
lol.. You misunderstand again. I said "it's spec" I was talking about the speed the CPU is specced to run the ram at. For example, the Athlon IIx4 only supports up to 1066MHz. If I were to put 1600MHz in that system, would it run at 1066MHz by default because of this or would it be run at 1600MHz?

Actually, if you would combine my previous posts, you would know the answer to that question. However, I'll help you out a bit.

First, about the Athlon supporting up to 1066, I refer to my post about where I used the i7 as an example. It's just what Intel/AMD says but these cpu support way faster ram easily. It's more a question about whether the mobo supports it.

And yes, it will run at 1066mhz stock, but just like mindless728 said, you can easily raise the clock using the mp's and some ram even has special profiles (ie. xmp) which enable you to set them at their rated speed, voltage and timings at the press of a button.
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a c 131 à CPUs
July 26, 2010 8:50:50 PM

Best answer selected by Enzo Matrix.
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