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i7-870 PC for number crunching

post #1 of 7
Thread Starter 
Hello to all!

I am a fairly seasoned PC builder who usually looks for stability and reliability more than extreme speeds. I ordered the components for my new PC (workstation), which I will use to do a lot of computer simulations, number crunching in anger, for a few hours at one time. I have got the following components:

Processor: i7-870
MB: Asus P7P55D-E PRO
Memory: 4 X 4GB Patriot Vider II Sector 5 DDR3-1600 (7-9-7-21/1.65V)
Disks: 2 X WD Caviar Black 500GB SATA III (6Gbps) for RAID 0
Video: nVIDIA Quadro 2000
Cooler: Thermalright Ultra 120 Extreme + 120mm Nexus Silent PWM fan
Power: Corsair AX850

I want to build a powerful computer on which I hope to do some engineering applications work (hence the Quadro/CUDA), with loads of computation-intensive mathematical simulations. My goal is to utilise the memory at its best (to achieve the timings it has stated), and to overclock the CPU to a safe level. I believe the cooler I chose will help me with keeping the temperature levels safe. I need to have enough computational power and to be able to leave the simulations running for hours on end, so stability must override any bold overclocking targets.

I will start to build it in the next day or two, and by the time I have it up and running by the end of next week to be able to try its stability in overnight runs. I am thinking of using Prime95 as an overnight test, and probably hitting it with some 3D benchmarks at the same time (suggestions welcome). Please feel free to suggest other ways to test its stability.

Based on my understanding, DDR3-1600 has an actual base clock of 200MHz, multiplied then to 8. The processor uses a BCLK of 133MHz x 22 (ratio) = 2.933GHz. Is my logic right in that if the motherboard supports a CPU : DRAM ratio of 133:200 = 2:3 (which some screenshots off the Internet suggest), I should be able to have the memory running at its specs, with only the timings left to be adjusted?

If I then want to overclock the processor, as well as the memory, I would need to raise the BCLK. Is it right to expect a medium stable overclocking BCLK of 160 X 22 (CPU ratio) = 3.52GHz? In this case, in order to use the memory at its rated speed I would need a CPU : DRAM ratio of 160:200 = 4:5 (which, again, some reviews on the net suggest it can be done on my MB). Are my expectations plausible?

I also understand that I would need to disable Turbo Boost, C1E,and SpeedStep, which I don't mind, as the computer will be doing something useful most of the time. I also understand that Hyper-Threading may reduce my chances of overclocking, although the software I use is said to benefit (as per its users) from Hyper-Threading by about 20-30%.

All suggestions welcome, as are any suggestions to test its stability, or what settings to be considering for my build. Again, stability is more important that raw instant performance, but I read that the i7-870 has quite a bit under his bonnet to squeeze a bit more performance (20% is my target, as per the above). Also, how will the fact that I am using all DIMM slots going to be affecting my ability to run the memory at its stated specs?

Thank you very much for reading and I am looking forward to hearing from all of you!

Cheers!
post #2 of 7
That was to long for me to want to read but the only part i caught was the turbo section. And on the 870 turbo disabled/on did not affect my overclocking ability either way.
But with turbo disabled [which I prefer] gives you real 4 core clocked at you desired mhz as opposed to turbo enabled which would activate and deactivate cores depending on the speed you're clock in. The higher the speed the less core become available.

And using all the dimm slots will make you up the voltage some, so if your looking for something like 4.0 ghz which its quite achievable on this chip it will take you a bit more effort to find a stable configuration or setup than say if you only populated 2 dimm's. But that its purely on my experience alone.
Edited by Haze80 - 2/20/11 at 3:52pm
Wayne-The-Brain
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Wayne-The-Brain
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post #3 of 7
Thread Starter 
Thank you for your quick replay, Haze80. I see your point on the Turbo, and it makes sense. Thanks for that.

On the memory side, do you suggest I may have to raise the memory voltage to make sure it copes with there being 4 DIMMs? The DIMMs are rated at 1.65V, and I read that the memory voltage should not be more than 0.45 above the processor voltage, which by default seems to be 1.145. therefore, if I am to run the memory at its stated speeds and voltages, I would need to raise the processor's voltage to 1.20V. Is this correct?

Also, in your experience, what is the safe temperature not to be exceeded by the processor (using Real Temp) when running Prime95 with HT turned on?

Cheers!
post #4 of 7
Well I wouldn't touch the memory voltage leave it as is.
Now here's some things I learned on my 870 while trying to overclock it.

Disabling hyper threading can reduce your temperatures under full load a good 10c and maybe a few 1c or 4c while idle. So if you see your temps rise to much while overclocking disable h/t.
From what I have found on these forums our processors perform optimal at 3.8ghz anything after that its minimal gain when compared to the 3.8 ghz mark.
Temperature wise I would really hate to see my processors hit anything higher than 74c 75 c under full load while some people say its ok up to 80c. But I believe you can easily achieve lower than 70c at 3.8ghz. 4.0 will bring the temps closer to the 70c under full load with decent cooling in my experience.
Also remember the lower your voltage the lower temps you will see just make sure to test your processor and memory for stability.
This is what I like to use to test the memory it really pushes your system to check for instability.
Remember to keep and eye on the temperature And try to keep the temps in lower 70c if possible under full load.
LinX v0.6.4
http://www.xtremesystems.org/forums/...d.php?t=201670

I also like to use prime 95
http://mersenne.org/freesoft/#upgradeusers
good luck with your overclock
remember all chips are not created equal so tweak yours to your liking until you feel comfortable with what you have.
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Wayne-The-Brain
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post #5 of 7
Thread Starter 
I set up the computer last night and it was an absolute pleasure. It took me seconds to set the memory to DDR3 1600 by loading the XMP settings, and leaving the BCLK to the default 133 MHz. I left all the other options on, including Hyperthreading and SpeedStep and the lot, and I ran prime95 on the 8 cores with a Direct3D application running as well through the night (about 8 hours) with no errors, but with the case panels off. I noticed the temperatures of the cores reaching a maximum of 56-59 Celsius through the test, but CPUz and Real Temp i7 GT reported the frequency of the processor to be 133MHz X 24 = approx 3209 (varying slightly), which suggests to me that Turbo is applied to all cores, by an additional 2 BCLK. Is my understanding correct?

Also SiSandra reported the memory bandwidth as just over 18GB/s, which I am very happy with, I don't think I'll be fiddling with my memory anymore.

The computer is now running a second batch of similar tests for stability, and the next step will be raising the BCLK to 160 and leaving everything unchanged (memory multiplier from 12 to 10 to get 1600), and if the system behaves itself without errors during my tests and the temperatures are in check, I believe I will be done with it. I will keep you posted how it goes.

Cheers!
post #6 of 7
Yes your are correct with turbo enabled the max is about 3.2 or 3.4ghz cant remember for sure but anything higher than that at turbo mode means its only running at 1 core at a maximum speed of abou 3.6 ghz. These little processors are very quick in ther factory state. Im glad yours is working out for you too.
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post #7 of 7
Quote:
Originally Posted by worker View Post
Based on my understanding, DDR3-1600 has an actual base clock of 200MHz, multiplied then to 8. The processor uses a BCLK of 133MHz x 22 (ratio) = 2.933GHz. Is my logic right in that if the motherboard supports a CPU : DRAM ratio of 133:200 = 2:3 (which some screenshots off the Internet suggest), I should be able to have the memory running at its specs, with only the timings left to be adjusted?
I'm confused by your RAM ratios here. Two things effect the RAM frequency. The baseclock and the Memory Multiplier. In some BIOS the memory multi is invisible and just gives you the options based on your given baseclock. 2:6,2:8,2:10,2,12, 2:16. To my simple mind that seems a little confusing and I tend to just think of them as X6,X8,X10 etc. as the 2 of 2:8 is just taking into account the Double Data Rate.

That your RAM is spec at 1600 simply means that it has been tested and is guaranteed to work at up to 1600MHz.


Quote:
If I then want to overclock the processor, as well as the memory, I would need to raise the BCLK. Is it right to expect a medium stable overclocking BCLK of 160 X 22 (CPU ratio) = 3.52GHz? In this case, in order to use the memory at its rated speed I would need a CPU : DRAM ratio of 160:200 = 4:5 (which, again, some reviews on the net suggest it can be done on my MB). Are my expectations plausible?
Almost. 160 baseclock with a CPU ratio of 22 should be easily doable. A 2:10 memory multi would give you the 1600MHz. I'll point out here that most but not all current generation Intel CPU's tend to do better with a odd CPU Ratio. Simply meaning that on average it will usually take more voltage to run a 22 Ratio then 21 at the same Core speed.

Quote:
I also understand that I would need to disable Turbo Boost, C1E,and SpeedStep, which I don't mind, as the computer will be doing something useful most of the time. I also understand that Hyper-Threading may reduce my chances of overclocking, although the software I use is said to benefit (as per its users) from Hyper-Threading by about 20-30%.
For what you are doing there is no reason not to use Hyper threading. HT creates more heat and can use more voltage to get stable at the same core speed vs without ht. This can hamper the ceiling of a overclock. Making per say 4.3GHz without HT possible on air but only 4.1GHz possible with it due to heat limitations. At a more mundane 3.5-3.8GHz overclock the extra heat generated from it won't matter.

As far as Turbo goes. For the most part you are not going to want to use the full Turbo feature while overclocked. Look here for more info on Turbo. http://www.intel.com/support/process...pkw=(cs-032279) A +2 multi is available on all 4 cores as the first Turbo multiplier. On both my i7 930 and my i5 760 that first turbo multi is available for use and you can configure a 24/7 overclock with it. Just an FYI there as I don't have a 870 so haven't tested it out on that chip. I wouldn't worry about it though just a heads up in case you feel like messing with it down the road.

Also going against popular belief here speedstep can be used for power and heat savings when not at full load while overclocked. I don't suggest setting it up that way as a first overclock because it can be a little trickier but it can be done and in most cases works very well as long as you do your stability testing with it on.
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Monster IIr
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