DDR2 800 vs 1066 for overclocking

Chris January 31, 2009 at 14:32:22
Specs: Windows Vista
I read several threads across the internet and still haven't found a direct answer.

In my case, my motherboard specifications show it is compatible with the 800mhz memory and 1066mhz is not listed. I have a AM2 6400 processor that I plan on overclocking and I'm looking at buying more memory.

Would it be correct to say that the 1066mhz memory would overclock further when I overclock my CPU? I'm sorta new to overclocking now. I overclocked my older computers, but they were much simpler it seems.

I remember that a limiting factor in overclocking the CPU was the memory crashing at higher speeds. It was either drop the memory speed to 4/5 speed (or something along those lines) or increase voltage.

I was thinking that if I get the 1066mhz memory, since the motherboard will force it down to 800mhz, wouldn't I be able to push the CPU farther since the memory shouldn't crash until it gets back over 1066 overclocked.

Or is it that the 9x multiplier just isn't compatible with my motherboard and the memory will be forced to 8x, which basically doesn't help me since the base speed is what's being overclocked?

See More: DDR2 800 vs 1066 for overclocking

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January 31, 2009 at 15:36:05
"I read several threads across the internet and still haven't found a direct answer"

Forum threads aren't the best place to look for info. Have look searched legitimate hardware sites - Anandtech, Legit Reviews, Tom's Hardware, X-bit labs, etc.?

1. the memory controller in AMD X2's with a numerical model number below the 7000 series does NOT support DDR2-1066. If you install it, it will automatically underclock to DDR2-800. Only the Phenom based CPUs (X2 7000 series, X3's, X4's) support DDR2-1066.

2. when overclocking an AMD system, the trick is to overclock just the CPU. The HyperTransport bus, PCI/PCIe bus, & memory bus should be kept as close to default as possible.

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February 2, 2009 at 13:22:40
I was searching through Toms Hardware and found some threads, but they didn't exactly answer my questions, and once I registered I get an error when I try to access the forum. So I found a link to this site which I could post my question in. [edit]looks like its working now[/edit]

And I apologize, here are my Specs...

AMD Athlon64 X2 6400+ Windsor 3.2GHz Socket AM2 Processor Model ADX6400CZWOF

Foxconn C51XEM2AA-8EKRS2H AM2 NVIDIA nForce 590 SLI MCP Motherboard

I have looked on XbitLabs and Anandtech for information on how far I would be able to overclock the processor, but it has been a while since I looked at that. I was probably confused at that time too, which is why I haven't done it yet (along with the fact that it is pretty fast at stock speeds anyway).

I was under the impression that a 1:1 ratio between CPU and RAM was best. I also am under the impression that, at a 1:1 ratio, memory usually crashes before the processor does. Since my motherboard is going to drop the memory speed down anyway, I was hoping it would give the memory more room for overclocking so that I can push the CPU further.

Here's a thread I was just reading through, http://forums.overclockers.com.au/s... kind of somewhat confirms what I was thinking.

By getting the 1066mhz memory, the memory won't be the factor holding the speed back. On top of that, it seems I'd be able to tighten memory timings by getting the faster memory and running it slower.

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February 2, 2009 at 14:54:48
"I was searching through Toms Hardware and found some threads, but they didn't exactly answer my questions, and once I registered I get an error when I try to access the blog"

Why are you searching threads & blogs? The sites I listed regularly test CPUs, overclock the heck out of them & explain the do's/don'ts & why/why-nots...read the articles!



Here's a guide for you...it's a bit dated but should still give you some insight into AMD overclocking theory:


Other than that, you've got two issues that you need to understand:

1. the 1:1 ratio does NOT apply to AMD systems because there is no FSB. By definition, the FSB is the bus by which the CPU communicates with northbridge chipset, but more specifically, the memory controller which is built into the northbridge. The memory controller then communicates with the RAM. For optimal performance, it's best to have both the CPU & RAM communicating back & forth with the memory controller at the same speed...that way, there's no logjams or bottlenecks. This is the way Intel systems are built. So for example, if you have an Intel CPU that runs at 1333MHz FSB & you also have DDR2-800, you'd need to lower the RAM speed to DDR2-667 to attain a 1:1 ratio. You may be asking why? The answer is that is the 1:1 ratio relates to frequency, not DDR or QDR ratings. 1333MHz FSB runs at 333MHz frequency, DDR2-667 runs at 333MHz frequency...put it together & you have 333:333 which is the same as 1:1.

AMD abandoned this technology many years ago. On all AMD CPUs since the release of the socket 754, the memory controller is built into the CPU & they communicate back & forth at full processor speed. In the case of your 6400+, that bus speed is 3200MHz. The CPU/memory controller then communicates with the RAM on the memory bus, which runs at 400MHz for DDR2-800, or 533MHz for DDR2-1066 (Phenom based CPUs only).

2. the X2 6400+ is very close to being maxed out at 3.2GHz, that's why there's no 6600+ or 6800+ CPUs. AMD realized that 3.2GHz was the safe max for the X2 core & stopped at the 6400+. You *may* be able to get your CPU up to 3.5 - 3.6GHz, but that's about it. And that relatively small 300-400MHz increase won't translate into a significant performance boost, plus it *may* cause problems in terms of stability & temperature.

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February 4, 2009 at 17:24:23
Well, thought I already posted a reply, looks like a had a problem...

I'd really like to see the rest of the article in that last link, but the originating web site is no longer available. Any chance it is somewhere else?

So my last PC had an AthlonXP that I overclocked after a couple years and I understand how much different overclocking is now. Also, I knew it would only overclock a few hundred mhz when I bought it. I just want to get a little more out of it and 150-300mhz increase is great - still a 5-10% gain. But looking through some of the articles seems to confirm my thoughts.

Since a typical overclock using 800mhz memory starts with downclocking the memory to 667mhz and then pushing the FSB up, by using 1066mhz memory, which is automatically downclocked to 800mhz by the motherboard, I should be able to push the FSB further without downclocking the memory again to 667mhz. Is that correct?

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February 4, 2009 at 17:36:58
Get the term 'FSB' out of your vocabulary. There is no FSB. AMD hasn't used it in years. All AMD systems use the HyperTransport bus.



I believe this is the article you were asking about:


If you want to see any of the other pages related to that article, simply replace short-media.com with icrontic.com in the web address.

I think I can save you the trouble with your overclocking. Just lock the PCIe at 100MHz, disable Cool 'n' Quiet, disable all Spread Spectrum settings, raise the CPU frequency to 215MHz.

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February 5, 2009 at 07:35:22
I know FSB is wrong, I just wasn't sure on using HTT in its place or some other acronym.

Awesome, thanks for the info on that link. I look forward to reading it tomorrow sometime.

Another thanks for the overclocking info, I remember reading about turning off cool-and-quiet for instability issues when it tries to lower the multiplier while it is overclocked, and I remember something about spread spectrum, but I don't recall anything on locking the PCIe mhz. I also plan on overclocking my video card, a EVGA 7600GT, which I have not yet researched.

And my question still stands. Should I be able to get a higher increase in HTT, or what ever you would call the base, core frequency, using 1066mhz memory over 800mhz memory on an 800mhz memory motherboard.

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February 5, 2009 at 08:50:45
From the above article:

"Overclocking the HTT bus: Is it beneficial?

In short, overclocking the HTT bus is not beneficial. Unlike the FSB in older platforms, the HTT is in no way a bottleneck that limits system performance. There has been some benchmarking done in the past and any performance gains were often within the margin of error. The system is simply not utilizing the HTT bus to its full potential. Increasing it does next to nothing for performance and can begin to cause system instability if it is increased too much."

Regardless, if you increase the CPU frequency from 200MHz to 215MHz, both the HT & memory buses will automatically increase along with it.

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February 5, 2009 at 09:33:39
So I have read part two of that article now I've re-read part one and realize HTT was the wrong acronym, as I thought, and found it uses the terms base or reference frequency, which is also the base for HTT and pretty much everything else too.

Since overclocking this base frequency inherently overclocks the CPU, HTT, and memory all together, even though I won't see a performance boost from the overclocked HTT, it still gets overclocked regardless.

That is unless I decrease the HTT multiplier, which I probably will not have to do since I will not be able to overclock that far anyway. If I'm able to get the base frequency up to 215-220mhz, that puts the HTT bus at or under 2200mhz, which is borderline in the safe range for 939 processors. My HTT bus at stock is running at 1000mhz, according to Everest, and I assume 2000mhz DDR, which matches the 939 processors. I figure the same range applies to my AM2 125W X2 6400 processor, but I could be wrong.

Anyways, I get that part of overclocking and the actual process of overclocking, the tips are great though.

My original question still remains...

Without changing any multipliers (or even with), will I be able to get a higher "base/reference" frequency using 1066mhz memory which is automatically downclocked with a 800mhz motherboard, instead of using 800mhz memory which, as far as I understand at this point, I should downclock to 667mhz to get better overclock speed?

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February 5, 2009 at 11:00:25
"My original question still remains..."

OK, you've got a grasp on the HTT. As for the memory, just set it to DDR2-800 & overclock the CPU frequency to 215MHz or whatever you can get out of it. Since the RAM is capable of DDR2-1066 (533MHz) anyway, there's no reason to lower it to DDR2-667. Even if you had DDR2-800 there probably would be no need to lower it...the reason being that you're simply not increasing the CPU frequency that much.

I don't know if the program I list below will help explain or not...it was designed for S754/S939 systems that use DDR RAM (not DDR2). Play around with the different reference clock, memory divider & multiplier settings...hopefully it will give you an idea of the relationships.


Take a look at this chart as well. This was posted in another thread just recently:


Here's where it came from:


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