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i7, BCLK and the unCore

S

Supersonic64

Senior member
So I've been reading a few i7 overclocking guides pending the arrival of my i7 920 next week and they have me a bit confused.

After reading a few guides, it is my understanding that the BCLK is tied to a bunch of other settings and that changing it automatically affects those other settings.

My concern is, I want to hit 4.00GHz on my i7 but I don't want to accidentally automatically overclock the unCore components past safe tolerances.

Also of concern is the QPI, I don't want to jeopardize stability by having that set to high.

How would this be achieved? Pardon my ignorance, I'm just having a hard time understanding this whole BCLK i7 overclocking procedure and want to be ready when I get my hardware!
 
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Overclocking the uncore is just like overclocking the execution core. It has a multiplier tied to bclk and you want it to run as fast as it can without crashing. There are significant gains to be had with a faster uncore (especially when the core is running 1.5+ GHz faster than normal) and it follows directly from increasing the bclk.

Take your vcore off "auto" and set it to something solid like 1.275 and start notching up the bclk incrementally until you have stability issues and then back down a tad. See how far you go with 1.275 volts. Your BIOS should give you 10 memory slots for you to save/improve upon your stable settings. Just experiment. If you are serious about 4 GHz we should talk about cooling.
 
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So I am assuming that overclocking the unCore is harmless unless I over volt it then? Is adding voltage to the unCore necessary to bring about stability? If so what is the safe limit.

Also, I purchased G.Skill PI DDR3 1600 (3x2GB). I will need to clock it down in the BIOS to 1066 or 1333 prior to overclocking correct?
 
The two 920s and one 930 I had needed between 1.3V and 1.4V for the VTT in order for a 3.2GHz to 3.6GHz uncore clock speed to be stable. The uncore has to be double the memory speed for regular i7s. At 1600 DDR you would need a minimum of 3200MHz. At 1800, 3600MHz, etc. The i7 980x can actually go as low as 1.5x the memory speed for better memory overclocking. The memory in my i7 980x system runs at 2040 DDR with the uncore at 3400MHz with 1.30V. Couldn't run the memory that high with any other i7 CPU.
 
Adamk47 has it spot on. Uncore uses a separate multiplier, usually 2x or sometimes slightly greater than the memory ratio. (For gulftown it is 1.5x)

To oc both memory and the uncore, you need not vcore, but rather VTT. (sometimes called uncore voltage or QPI/VTT.) Remember to keep this under 1.35v if possible.

So to conclude, set the VTT to a normal setting, say, 1.275v, and up the bclk, adjust memory and Uncore multies as desired (say u have 200 bclk, and DDR3 1600, use the 8x multi for memory, and >= 16x for uncore) and of course adjust vcore for stability as well. (start around 1.3V?)

The rest is just ocing and stability testing, with settings adjusted as needed.
 
My main concern is not to go over safe voltage limits for the vCore and VTT. I'm using air cooling and don't want to kill the chip.

You guys think a Xigmatek HDT-S1283 with bolt-through kit will sufficiently cool an overclocked i7 920 and keep it under 70c?
 
usapatriot said:
My main concern is not to go over safe voltage limits for the vCore and VTT. I'm using air cooling and don't want to kill the chip.

You guys think a Xigmatek HDT-S1283 with bolt-through kit will sufficiently cool an overclocked i7 920 and keep it under 70c?
Click to expand...

I hope so, but I tend to hit load temps mid 50s at stock without HT and low/mid 60s with HT on with that cooler, and that's with a slight cpu undervolt. My guess is that the cooler won't handle cpu voltage increases all that well, so if you are still shopping might want to keep an eye out for something a little more capable.
 
I'd suggest CORSAIR's H50. I have one and love it so far but haven't really gotten into the nitty gritty of testing it out yet. Just got my new system up and running. In due time though.
 
Check this out, what do you guys think? I know temps are a little high, I need to order a better cooler. I'm actually still dropping the vCore and VTT...

 
Looks like your temps are peaking at 80C. The change that will drop those load temps the most is to disable hyper-threading. I wouldn't be surprised if that drops the load temps to lower 70s. If you aren't encoding, you don't really get any benefit from HT anyway.
 
Yes, so I've heard, I just want to get an idea of what my absolute maximum temps are. Besides, these temps are unrealistic in real-world usage, only Prime95 and LinX get them this high. I'm downloading 3DMark Vantage now to run some tests.

Here are my current settings:

191 x 21
unCore x 16 / Mem x8
QPI x18/x36
vCore 1.25000 BIOS / 1.264~1.232 Windows
VTT 1.315 BIOS
IOH: 1.100
DRAM: 1.500
LLC: Level 02 to minimize vDroop
 
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