Could someone clarify a ram frequency query for me?

[boing]

I need to expand my RAM from it's current 8Gb to 16Gb and wanted to check i'm not wasting money on memory that won't benefit me, despite having read a few articles on timings and frequency i'm still not confident in my understanding of it all.

Firstly my system and useage. I use 3Ds max 2012 and am currently hitting my memory limit enough to warrant more RAM. Speed is of the essence (within my budget) as an animation could be a few thousand frames long and even 1 minute more per frame will murder me on a job. This is my current system.

Motherboard .............. Gigabyte GA-P55-UD4 http://uk.gigabyte.com/products/product-page.aspx?pid=3161&dl=1#ov
CPU .......................... Intel Core I7 860 http://ark.intel.com/products/41316
RAM ......................... 8Gb DDR3 1333MHz PC10666 (8-8-8-24) G-skill ripjaws http://www.gskill.com/products.php?index=224
Graphics ................... Radeon HD 5850
OS ........................... Win 7 64 bit
Heatsink ................... Coolermaster hyper 212 plus http://www.coolermaster-usa.com/product.php?product_id=2923

I'd like to lightly overclock my CPU, not sure by how much but I want it to be rock solid and require no more cooling than it currently has, so as I say it will be moderate (3.2 Ghz?) I'm mighty tempted to go for 3.8Ghz as speed is important to me but if the system is unstable I'm buggered so I might just take it easy there.

Here are my questions.

1) Does the over clocking of the CPU impact the speed of memory I need?
2) Is this correct? (FSB frequency/number of cores) x 3 (if using DDR3 RAM) = mem frequency
3) CPU-Z lists my current memory frequency as DRAM 661MHz, how does this relate to the 1333MHz listed frequency?

Any help is appreciated, thanks.

 

[greenhawk]

you need to remember that even if over all the ram is slower, it is still miles and miles and miles faster than letting the computer use the HDD / swapfile when low on memory.

As to the overclocking, if you must have solid and stable, then overclocking might not be worth the effort to ensure a good overclock. A small overclock might not be noticed, espically if the hdd is being used heavly. Though if you are limited in cpu performance, then even 5% overclock could be noticed for long runs.

Though the i7-860 is 2.8Ghz with a turbo of 3.4 (single core, or 2.93Ghz for 4 cores)). And IIRC that range of cpus does not overclock as well as the current sandybridge cpus, so not sure if overclocking to 4 cores at 3.8 is likly, but I have not paid any attention to overclocking of that cpu.

Secondly, you will need to overclock the FSB for that cpu, so RAM becomes important unless you run it slower than it's spec. Might not be a issue but benchmarks might say otherwise. Testing is the only way to be sure.

as to the questions.

1) only if you want to keep the ram at the same speed as the FSB increases. Otherwise most motherboards allow you to run the ram slower and so does not effect a CPU overclock.

2) number of corse has nothing to do with the FSB to CPU clock speeds. It is just the clock multipler. Secondly, DDR is always 2.

Going from memory, the default FSB on the cpu is 133Mhz. The cpu's multiplier (i7-860) is 21. Ram is 1333Mhz effective, so FSB is 666Mhz actual. That difference is just used to allow for the difference in data bus widths IIRC.

so if you increase the FSB from 133Mhz to say 140Mhz without changing anything else, you will have your ram running at effectivly 1400Mhz (might work, might just need to loosen ram rimings) and the CPU would have a base clock of 2.94Ghz (then 3.08Ghz for 4 core turbo and single at 3.56Ghz).

Of course, due to the turbo feature, getting a stable overclock needs some checking of your chips performance with turbo disabled (so you know at that speed the cpu fails at). Then you can setup the speeds taking that into account so turbo does not go over the "known stable" speed.

3) CPU-Z is reporting the actual speed as DDR, as the name sugests, Double Data Rate uses the rising and falling edge of the clock, so the effective rate is twice the actual rate. So if it says your ram is running at 661Mhz, then the current effective speed is 1322Mhz, a little slower than the full 1333Mhz. Not a big variation as just a small difference might come from how CPU-Z works it out.

 

[boing]

Great, thanks greenhawk, very comprehensive answers.