Core i7/X58 Overclocking Thread

[dejanh]

dejanh, I'm having some trouble with the ratios theory here.

I've had two different settings pass 12h ond 8h Prime95 stable on two different bios versions and it definitely doesn't follow the "rule" you stated.

Setup number one does not follow the rule but it's stable. Setup number 2 does follow the rule and is also stable. The one constant is that the QPI stays below the 4GHz threshold. Could that be all that's required?

I've also tried on bios F4k and I've been having some stability issues with BOINC that I haven't worked out yet. Of course, all of this on the stock cooler doesn't help.

1) Bios F2 - Bclk 160 - RAM 10x - UC 20x - QPI 18x


2) Bios F4l - Bclk 200 - RAM 8x - UC 16x - QPI 18x

Glad to have some feedback! The more discussion stirs up, the more we can dissect the intricate aspects of i7 overclocking

1. In terms of the QPI having to stay below 4GHz, yes, this is definitely correct. QPI higher than 4GHz will not run on 99.9% of the boards and chips. This is critical.
2. In terms of the Uncore:QPI ratio of 8:9...I think I edited the original post the next day to reflect some people saying "I'm running Uncore higher than my QPI". While this is very possible I found that this is (a) not stable when dealing with high clocks (3.9GHz+) at least in my test setup, and (b) not exactly an option on i7 920 and i7 940 when you get to high clocks at all as you are driving your DRAM, Uncore, and QPI all based on the same high BCLK. If you use a 200MHz BCLK your lowest option for QPI is 3600MHz which is already getting up there. I tried running DRAM at 1800MHz with this and the Uncore with 3600MHz and I was completly unstable. Lowering the memory to 1600MHz (more within the ratio I defined) made the system more stable. Same holds up if I go to 180MHz BCLK with a 23x multiplier (turbo on i7 940). I put the QPI below Uncore to the test by assigning a 18x multiplier (3240MHz) to QPI and running my DRAM at 1800MHz (3600MHz Uncore). The system was unstable. Then I restored the QPI ratio to 22x for 3960MHz and the system was once again stable.

Overall, the 8:9 Uncore:QPI is not a hard rule. I just found it to be a "safe" rule in my testing. Adding to it you have to consider that Intel does not randomly spec out their processors. If they felt that ratios between different components of the CPU could be different, they probably would have set them up different, so there must be some reasoning behind their factory set ratios. They had the option easily to make the Uncore and QPI run at the same speed from the factory, or even higher, but they chose not to. I believe I found why they did that through my testing, and I do not think that it is just becase there is *maybe* no performance increase in running Uncore more than 2x DRAM. Kind of like with AMD where on the X2 processors you had to keep your HT as close as possible to 1GHz to balance stability and performance. Much higher than 1GHz and poof, the system dies, much lower and you are sacrificing performance.