It has a FSB of Up to 6400 MT/s.
What you probably mean is that it has a QPI Link up to 6400 MT/s. QPI Link speed depends (default) on the BCLK setting.
The i7-920 has a QPI speed of 2.4 GHz. The i7-975 for instance has a QPI of 3.2 GHz.
When you overclock an i7-920 from the default BCLK of 133 to 172 (i.e. from 2.66 GHz to 3.6 GHz with Turbo on), the QPI frequency rises to 3.1 GHz. That also effectively increases DRAM frequency to 1372 MHz. While it is definitely possible to overclock DRAM more, it has two distinct disadvantages. You need to increase DRAM voltages as well going up to the maximum of 1.65V that Intel allows and pushing things to the limit is IMO not advisable in an editing machine. Second the temperature of the DIMM's, especially when all slots are populated, will rise and it is not easy to use a fan for cooling with the location of the memory slots.
To use DRAM frequency of 1800, you need a BCLK of 225 and the multiplier set to 16. Whether that will be stable, I don't know. Realise that all the un-core elements, memory controller, L3 cache and QPI are based on this BCLK setting and if these will be stable at 3.6 GHz memory controller and L3 cache and 4.06 GHz QPI is the question. Specially the QPI is much higher than designed. With the core multiplier at 16, you maintain a nice 3.6 GHz for the CPU.
Although somewhat dated, this article will give you some background on memory performance: http://techreport.com/articles.x/15967/1
PC3-14000 • Unbuffered • NON-ECC • DDR3-1800 would be the faster choice?
Theoretically, yes. Whether it is worth the price difference is doubtful. 1% difference in performance versus xx% in price?
Conclusion from the TechReport:
Most enthusiasts do have budgets, though, and we're generally disinclined to swallow the exorbitant premiums associated with flagship gear, even if it is faster. I suspect most folks rolling their own Core i7 systems will stick with the Core i7-920. Unless you're going to push the base clock, which requires some cooperation from your motherboard, the 920 is essentially limited to DDR3-1066. At that speed, DIMMs with 7-7-7-20 timings are actually quite affordable and widely available, so there's really no need to settle for budget modules with looser timings. Our testing shows that you can even get away with a dual-channel config if you happen to already have a couple of DDR3 DIMMs lying around. I wouldn't skimp on that third memory module if I were building a Core i7 system from scratch, though.
Of course, many enthusiasts who spring for a Core i7-920 will be looking to overclock by increasing processor's base clock speed. Turning up the base clock allows for faster memory speeds, and given that the 920's memory bus multipliers are limited to 6X or 8X, you'll actually need DIMMs capable of running at faster than 1066MHz if you intend to push the base clock above 178MHz. Whether it's worth springing for DDR3-1600 modules over more affordable DDR3-1333 DIMMs will depend entirely on the applications you use and just how high you intend to push the base clock. You'll need to reach at least 200MHz to run 1600MHz DIMMs at full speed, and not every Core i7 motherboard is up to that task.
In the end, Core i7 processors will certainly achieve higher levels of performance when paired with faster memory, but you don't lose all that much—particularly with games and common desktop applications—by running slower, more affordable DIMMs. That's good to know for folks looking at the relatively high prices of fancy triple-channel DDR3-1600 kits. However, if you're going to overclock, it's worth having the extra headroom that faster modules can provide.
Did you have to tweak the mb or processor or did the system automatically adjust to the DDR3-1600 sticks you put in?
I'm not looking to overclock anything.
So you think that the performance boost between the - say - DDR3-1800, DDR3-1600, DDR3-1333 and DDR3-1066 is not significant enough if i'm not going to overclock and i should stick with the DDR3-1066?
If Jim is not overclocking his system, should he have saved a little bit of money and bought the DDR3-1066's instead of the DDR3-1600's?
Nothing is OC'd. The memory runs at the mobo set rate of 1066.
So if you where to have purchased DRR3-1800, the mb would have configured it to run at 1066?
Also, why did youy choose DDR3-1600 and not DDR3-1066 if the mb dumps it down to 1066 anyway? Just in case you want to OC in the future?
On a side note...
You and Harm are complete opposites! He gives you way more info than you want to know, no offence Harm - i like all the info, and you give barely enough - i guess your just a man of few words?
I bought the 1600 because it's the max supprted by the motherboard. I didn't know at the time that getting it to run at 1600 would be considered overclocking. But running synchronos memory can have an advantage, so I left it at 1066.
Well..... Don't write about an advantage and not tell me what it is - so get it up dude!
What Jim implies is that you best use either a hex kit or two tri-kits for your memory.
If you don't overclock, 1066 memory is what you want, if you may consider some overclocking in the future, use 1333 memory. Using 1600 requires heavy overclocking to be used at full potential. All memory will throttle down to the frequency of your system, even very expensive DDR3-2000.
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By synchronos here I mean running the memory clock and the CPU clock in tandem. Benchmarks have shown that running DDR2 memory at 800 to match the FSB can actually give better performance than running a faster memory clock using that same 800 FSB speed.
Now granted, those benchmarks are somewhat old and were taken when the memory controller was part of the North Bridge. The i7s now have it on the CPU die itself, thus greatly improving performance. But I'm assuming the idea holds true.
thanks to the both of you.
Just one more question....
I have looked at the P6T SE page on the ASUS site and other than the list of supported memory, i can't see where it says the mb set rate is 1066 thus use DDR3-1066 if not OCing? Or is it aways based on the last and slowest supported stick on the list?
At default the i7 runs at 2.66 GHz, with a multiplier of 20, so 2666 MHz / 20 = 133 BCLK. With a DRAM multiplier of 8, this results in 8 x 133 = 1066 DRAM frequency.
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>can't see where it says the mb set rate is 1066
That information is on the Intel page for the i7 on-chip memory controller, so carries through to ALL motherboards for the i7 having a "standard" memory clock of 1066