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Last response: in Overclocking
February 12, 2009 10:56:18 AM

How does the different voltages influence the stability regarding the CPU, the memory etc? For instance, if I know the memory is limiting the overclocking, which voltages are then worth raising? Or if I have a good marigin on the mem sticks, but the CPU is limiting, which to raise? I also would like some input on reasonable levels. I should say that Im talking about Intel C2D (and C2Q) processors here.

Vcc: Ok, this makes the CPU stable. And if reading the processors spec. there is recommendations about maximum voltage. As a general rule, 1,5V with 65nm and about 1,175 with 42nm, right?
Vdimm: This is clear too. Stabilises the memories which are specified for a certain voltage. But most mems work with 2,1V, right?
Northbridge Voltage: Stabilises the communication with the CPU and memory, right? But, what is a reasonable voltage? In my P5B-E BIOS the default level is 1,25V and the next is 1,40V, which looks like a big step to me.
FSB Termination Voltage: Helps stabilise the CPU? How about the memory? I have red that more than 1,3V is risky. Correct?
Southbridge Voltage: Do I ever want to raise this one? It just affects SATA, PCIE and PCI, right?
ICH Chipset Voltage: Do I ever want to raise this one?


More about : voltages

February 12, 2009 6:58:35 PM

a b à CPUs
a b K Overclocking
February 12, 2009 7:10:10 PM

Well to start 45nm processors (most) have max of 1.3625v vcore as per the spec sheets. Then again if you check out the data sheets it's usually around 1.45v max vcore.

Vdimm, manufacturers specs are about all you need.

Northbridge, will depend on you OC (as well as most of the other voltages you set), if you are interested in extreme OCing I'll give you a link to testing done at the upper end of the voltage scales without harm to the chips.

Are you trying to OC something ?
Related resources
February 12, 2009 8:09:40 PM

Im overclocking my E6400 and right now I am stable at 3,15GHz and Vcc=1,3000V (CPUcase 49 degrees at load). The processor can do better but I have trouble stabilising my memories over 394MHz, neigher raising Vcc or Vdimm seems to work. I have a feeling that stepping over 400MHz, lets say to 402MHz, and raising the NB voltage helps a bit but 1,4V doesnt seem to be enough and Im not sure it would be healthy to raise it further. Furthermore, I dont know if it would be of any help to raise FSB Termination Voltage at this stage, have tried 1,3V but it didnt do any differance.

I guess what I really want to know is how much I can push the northbridge. At 1,25V with this OC it goes 45 degrees after a while. Is 1,4V ok and could I raise it further? How warm is ok?

I also want to know if raising FSB Termination Voltage is of any use in this case when the memory is the limiting factor.

Thanks in advance
February 12, 2009 8:10:45 PM

Somehow my signature got lost so here it comes:

Asus P5B-E
Intel Core 2 Duo E6400 B2 @ 3,15GHz
4x1GB Corsair XMS2-6400 Xtreme
PowerColor Radeon X1950Pro 256 MB
Hiper 530W
a b à CPUs
a b K Overclocking
February 12, 2009 8:40:17 PM

OK, lets start by getting rid of two sticks of ram (for the moment), keep the two in slots 1,3.

1.4v NB if fine. If the NB is getting hot, remove the heatsink, clean and reapply with AS5 or similar. Still hot put a fan on it, but you shouldn't need to.

You really shouldn't have to raise your vtt at this point.

Raise your vcore to 1.45v (keep an eye on temps). Specs 61.4 thermal, 1.5vcore.

Let me know.

February 13, 2009 10:49:37 AM

Thanks for your suggestions. I removed 2 mem sticks and raised the Vcc and it appeared to be stable at FSB=402 so I raised it further to 413 (3,3GHz). With following settings it POSTs and Windows starts as well. But it fails at once on the Prime95 Blend test. It is always Core1 that fails. The temperature at load seems to be around 55-56 degrees and my Zalman CNPS9700AT finally has to work ;) 

Vcc = 1,4000V-1,4750V Makes no differance.
FSB Term. V = 1,300V
Vnb = 1,40V
Vdimm = 1,9V (stock)-2,1V Doesnt seem to make no differance.
5-5-5-18 (stock)

So, the bottom line might be that 413GHz is a little too much. I think it´s the Northbridge voltage that is´nt enough but I dont think I dare to raise it further. What should be a healthy maximum?

Another strange thing I noticed was that if setting the memories to 6-6-6-18 the computer doesnt POST(!) It looks like too slow memory sticks might limit the OC as well. Can someone confirm that?

a b à CPUs
a b K Overclocking
February 13, 2009 2:12:40 PM

826 mhz may be too much for your ram. To find out lower your multiplier (to take the cpu out of the equation) and raise the fsb to see how far you can take it.

Have you set your memory sub timings?

Try 6-6-6-24 to loosen your memory timings if you need to.

Do you have memory Skew settings in your Bios?
Have you taken all voltage settings off auto?
GTL ref settings?
February 13, 2009 5:46:30 PM

Well, my memory timings are set to 5-5-5-18. As I wrote before 6-6-6-18 makes the computer not POSTing at this feq. 18 is max of what I can set.
Skew settings - I dont know what that is, and no, dont think I have that.
Alll votage settings are off auto.
And I have no GTL ref settings.

I´ll experiment with what freq. the memories can take

Another thing, my Vdrop is quite bad. At 1,4750V CPU-Z reads just over 1,4V. Maybe I could go even higher...
a b à CPUs
a b K Overclocking
February 13, 2009 6:34:25 PM

It looks like the latest Bios is v1803 (8-5-2008), if your not using this latest version you may want to flash it. It may give you more options.

February 14, 2009 6:50:05 AM

Well, I flashed to 1601 not long ago. That is the latest one that is not a beta. And according to the documentation the versions after 1601 only are for supporting CPUs with bus speed 1333MHz. While the P5B-E isnt officially supporting faster than 1066MHz I guess they have to call it a beta. But sure, it might be worth a try. Even if I wont get any more options it might make the board more stable at higher speed.