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The Big PCI-E Mystery.

Last response: in Overclocking
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March 25, 2009 5:04:03 PM

Hi,

I've spent a lot of hours on the net recently looking for a proper explanation of consequences of changing the PCIE bus frequency. Some ppl say it's dangerous and it can cause permanent damage of the GPU, others say that PCIE freq is just a data rate and as such can't cause any damage whatsoever. Some advise to leave it set to AUTO, others say to not to go over 120...

Needless to say I'm confused.

I've been messing around with my E7200@GA P31-DS3L for a few days now. It's set to 3.16Ghz (333x9.5) now. If I want to set FSB to 400 I have to either leave PCIE at AUTO or set it manually to 118 ( that's the lowest setting I found by hit&miss ). My PC won't POST otherwise.

I'm a noob when it comes to overclocking, a very confused noob.

One more thing: Is there any program that can read PCIE freq? I'd like to know what's happening when it's set to AUTO. EasyTunePro doesn't show anything.

More about : big pci mystery

a b K Overclocking
March 26, 2009 12:42:11 AM


Are you OCing with EasyTunePro?

Or are you entering the settings manually in the Bios?

March 26, 2009 1:56:27 AM

RJR said:
Are you OCing with EasyTunePro?

Or are you entering the settings manually in the Bios?


I do all the settings in BIOS. I used EasyTune just for monitoring.

BTW, I noticed another thing today: the lowest possible PCIE freq raises gradually with FSB freq. I can lock PCIE to 100Mhz only when FSB is set to 340 or lower, small example:

FSB / PCI-e
360 / 106
370 / 109
380 / 112
390 / 115
400 / 118

Some dude tested PCIe overclocking in this article:link, he pushed it to 125MHz, but it's an old post. So, maybe I shouldn't worry too much about setting it to 118...
Related resources
a b K Overclocking
March 26, 2009 3:31:13 AM


You should definitely be able to lock your PCIe at 100 mhz no matter what you have the FSB set at. If you can't something is drastically wrong in your Bios or EasyTune is presuming it isn't locked and giving you false readings.

I've seen parts fried from extended periods at even 110 mhz. It's really not worth the chance for the extra bandwidth that is completely unused anyways.

March 26, 2009 2:41:15 PM

RJR said:
You should definitely be able to lock your PCIe at 100 mhz no matter what you have the FSB set at. If you can't something is drastically wrong in your Bios or EasyTune is presuming it isn't locked and giving you false readings.

I've seen parts fried from extended periods at even 110 mhz. It's really not worth the chance for the extra bandwidth that is completely unused anyways.



It can't be BIOS as I tried all versions from Gigabyte's website (f8, f9, f10beta). Like I wrote in the first post EasyTune leaves blank space under AGP/PCIE, that's why I asked for a name of a program that can read PCIE freq from Windows. It's not that important though, as I enter all the settings in BIOS... any other ideas?
a b K Overclocking
March 26, 2009 11:49:23 PM


OK, let me see if I have this correct:

You entered in the Bios under PCIE frequency: 100 mhz

Then if you change the FSB (cpu host frequency) value to 380 it automatically changes the PCIE frequency (to 112) in the Bios without you touching it and won't let you enter 100.

Is this what is happening?

Strangest thing I've never come across. Bios pics with available PCIE options for the higher FSB settings would be of great interest if you would, and I'll see if anyone else has had this problem.
March 27, 2009 1:27:23 AM

No, it's not like that at all... :non: 

If I set the FSB freq to 380, I must enter at least 112 under PCIE, otherwise my PC will reset all the BIOS settings to default values after I hit F10 (save to CMOS and exit).
March 27, 2009 2:18:43 AM

OK, I did some pictures:

FSB set to 400 with PCIE at 100:



Knowing it's not going to work, I hit F10 and after few moments my PC boots with following settings:



As you can see, all the settings are reverted to default, except multiplier which strangely stays at 9 (it's 9.5x266 by default).

The whole point behind my questions is that one could set his/hers PCIE to AUTO and not realize that it's not gonna be 100MHz, risking damaging GPU or SATA drives... There's a P35 overclocking guide on this forum, just a few posts below mine and the guy says to set PCIE to 100 or leave it at AUTO... well it looks like it's not such a good idea, not in my case at least...
a b K Overclocking
March 27, 2009 2:04:45 PM

OK, we are getting somewhere now. Most OCing guides will tell you to lock your PCIe to 100-105 just so it doesn't do any damage.

If you would supply some pics of the Bios settings you are trying and not working I can hopefully try to figure this out with you. Yes, if you just set Fsb:400 and PCIe:100 it definitely wouldn't work without setting your NB,PLL,VTT,CPU,etc.

and for the 9.5, it's under fine cpu clock, just put in .5 (Yes, strange it doesn't default to this).


March 29, 2009 6:06:45 PM

First of all, many thanks for your replies, RJR.

I've found the answer to my problem, I think:

Aussie overclocking forum

It looks like it's a common problem with Gigabyte's P31 motherboards. In other words I'll be doing some shopping soon ;) 

Thanks again for your help and best of luck to you, dude.
April 1, 2009 12:26:42 AM

do you have a motherboard in mind now, andy?
April 1, 2009 11:45:30 AM

antemon said:
do you have a motherboard in mind now, andy?


I'm going for GA-EP45-UD3L, decided to stay with Gigabyte as their BIOS is easy to understand for a noob like me.
You should start a new thread, antemon - I'm a noob and there are a lot of ppl here who are way more experienced than me and will be more than happy to recommend a good mobo to you.



For all those unfortunate poor souls who own a P31-DS3L:

I've found another info regarding the PCIE setting. If you want to set the FSB higher than 333Mhz use the equation below to calculate your PCIE freq:

FSB / 3.33 = PCIE
April 3, 2009 2:02:58 AM

Hmm, most motherboards make it easy by having a setting to async the FSB and PCI-E clocks.
April 5, 2009 7:54:27 PM

I finally got it clarified by one of the moderators on Gigabyte support forum.

His response:

Budget boards such as P31 or P43 will need PCIE set to above 100 for overclocking generally. Auto is not advised because when you raise the FSB the PCIE Freq will also increase automatically.

I suggest 100-110 as a safe range, but anything above 100 can damage your board/GFX Cards, and Hard drives. So it is all up to you, but manually set it for sure.

If you want to run 400 FSB, and have to use 118 I do not suggest that or you will damage something for sure. I suggest a new board, P35 if you do not have much money, or P45-UD3x models are all around $90-120


link to my thread


I had read this review before I bought this board, they pushed it to 465mhz, that would give a "healthy" PCIE frequency of 140mhz. I can almost smell their GPU frying... :ouch: 
April 5, 2009 9:25:53 PM

Not only their GPU, but anything over ~120mhz can cause corruption of data on SATA hard drives.
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