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Can't overclock CPU without OCing PCI-E bus

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  • CPUs
  • Overclocking
  • Bus
  • PCI Express
Last response: in Overclocking
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April 23, 2008 1:01:41 PM

At the moment, I'm trying to overclock my E6300 with my GA-945P-S3 motherboard.

The problem I'm having is I can't get stable overclocks without overclocking the PCI-E bus. Like serious overclocking. To get past 2.4GHz I have to push the PCI-E bus frequency above 110MHz, and from what I've heard this doesn't seem right.

I've tried changing Vcore, FSB over voltage, DIMM over voltage and all that jazz, to no effect. It only POSTs above a 300MHz CPU Host Frequency if I overclock the PCI-E bus in line with the host frequency overclock (e.g. 100 -> 110 -> 115 etc).

My setup:
Processor: E6300 (1.86GHz)
Motherboard: GA-945P-S3
RAM: Corsair DDR2 XMS2 (667MHz, 5-5-5-12 timings)
Cooler on processor: Thermaltake Big Typhoon 120VX
Case: Antec Nine Hundred (2 x 120mm intake, 120mm side intake, 120mm rear exhast, 200mm top exhast)
PSU: Corsair HX620W
GPU: MSI NX 8800GT (factory overclocked)
Grease: Arctic Silver 5
HDD: 2 x 250gb

Theoretically I should have plenty of cooling, so I don't think that's the problem. Overclocking the PCI-E bus frequency worries me, and not being able to overclock without it worries me even more. Unfortunately, google hasn't been much help.

More about : overclock cpu ocing pci bus

April 23, 2008 11:55:52 PM

That is a interesting problem. According to MSI's website, it's safe to go up to 120Mhz on the PCI-E frequency, and I'm sure the 8800GT can handle that.

Anyways, by stable, do you mean at least 8hours stable in Prime95 small FFT's and 12hours stable Prime95 blend? Longer the better.

Try flashing to the latest bios.
April 24, 2008 12:05:48 AM

Bios is flashed to F6. I've heard version F5 is the best for overclocking, but I really don't think it should make too much difference.

I read somewhere else that you have to overclock the PCI-E bus to 3xFSB + 1 to make it stable, and my own results seem to be in line with that.

Is it something to do with the motherboard?
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April 24, 2008 12:14:56 AM

ryan_au said:
Bios is flashed to F6. I've heard version F5 is the best for overclocking, but I really don't think it should make too much difference.

I read somewhere else that you have to overclock the PCI-E bus to 3xFSB + 1 to make it stable, and my own results seem to be in line with that.

Is it something to do with the motherboard?

I dunno that rule, mine is perfectly fine without touching the PCI-E frequency.

Ocing the PCI-E frequency does increase the cpu clock speed, so perhaps that 1MHz OC makes your entire system stable?
April 24, 2008 12:25:46 AM

This is the lulz... :na: 

You should never overclock pcie so long as you can help it. It's a bad idea, and basically comes with no performance benefits. Graphics cards are expensive, don't risk burning it out.

Any half decent overclocking board should let you lock pcie frequency.
April 24, 2008 12:42:01 AM

Dagger, I don't think you understand my predicament.

I _cannot_ get stable overclocks past 300MHz cpu host frequency without overclocking the PCI-E bus to 3 x cpu host frequency + 1.

At the moment I am running a 347MHz cpu host frequency and a 117MHz PCI-E bus frequency. If I drop the PCI-E bus frequency any lower, I can't get a stable overclock. I'm thinking it has something to do with my motherboard.

Evilonigir i, could you please share your settings?
April 24, 2008 12:42:18 AM

dagger said:
This is the lulz... :na: 

You should never overclock pcie so long as you can help it. It's a bad idea, and basically comes with no performance benefits. Graphics cards are expensive, don't risk burning it out.

Any half decent overclocking board should let you lock pcie frequency.

Too true, but didn't you read what the OP said? He said without OCing the PCI-E frequency, he can not get his system stable. I'm thinking maybe it's some fsb hole...
April 24, 2008 12:49:55 AM

Are you using software or doing it manual in Bios?

I found this: The PCIe lock only functions if you set the memory multiplier to the magical '2.0-' setting. It was on a review of your board I found.

Try that, hope it works.
April 24, 2008 12:55:40 AM

roadrunner, locking the PCI-E bus is not the problem, it's that I have to overclock it to get my system stable at any decent sort of overclock.

I'll give that 2.0 memory multiplier setting a go again though, even though it hasn't worked in the past.

Oh, and I'm overclocking in the BIOS.
April 24, 2008 1:06:28 AM

Ok erm don't want to dumb down the the help, i know you've said you've tried all that jazz, but if you've left your RAM on Auto it'll i'm guessing have defaulted to 266 with lower than spec Timings so just increasing the vDimm won't work.

Could be a pointless hypothesis, however it's out there now... <-- look at me with my big words - lol

*Edit* I understand this doesn't explain your PCI-E temp fix, but as far as my depth goes it's one of those...do not fiddle with or you'll break summit thingers.
April 24, 2008 1:12:15 AM

closed_deal, RAM is not on auto. At the moment I've got memory multiplier set to 2.50, so the ram is running at about 868MHz.

I've also set CAS timings to 5-5-5-15.
April 24, 2008 1:14:27 AM

Ok that could also be the problem your specs say you've got 667Mhz RAM now to get 868Mhz is a ruddy good overclock on the RAM and is most likely the limit.

I'd suggest changing your multiplier further and trying again. If it still doesn't work i'm befuddled.
April 24, 2008 1:18:58 AM

I've pushed the RAM past 900MHz in previous overclocks (higher PCI-E frequencies) and it seems to be stable.

I'll drop the memory multiplier back to 2.0 and the RAM will be running at ~700MHz, so that should rule out a RAM overclock limit. As roadrunner said earlier, maybe that will help lock the PCI-E frequency (even though that doesn't seem to be the issue).
April 24, 2008 1:19:10 AM

Maybe your ram dont like to OC that much. Run 1:1 and how high of a vcore have you tried. If you have a good cooler start at 1.5 and work down til its unstable.

If it dont work I think 115PCIe is ok but I wouldnt go higher. Maybe you got a bum chip.

Is that old stepping or is it M0 stepping. How high have you got it to run stable? What is the multi on that
April 24, 2008 1:22:03 AM

Righto, this is the first problem I've heard in just over two years at overclocking that involves the PCI-E and increasing it to get better stability at fairly low clocks. It'll be interesting to find out what fixes this.

^^^^I agree with the 115Mhz max PCI-E
April 24, 2008 1:26:37 AM

Looks like you have B2 stepping and a 7x multi. Ouch! You be lucky if you get over 2.4.

You would be better off with a e21xx series as they are mo and have 8,9,10, multis. Or the e2200 at 11x multi is a bargain right now also. Also the e4700 that is new has a 13x multi. Now I'd like to see what that baby can do!

7x multi, old stepping, and old chipset is gonna hold you back.
April 24, 2008 1:47:59 AM

Really? I know a lad with an e6300 running at 3.0GHz with stock cooling.

Anyhow, I dropped the PCI-E bus frequency back to 100MHz, and so I can only get stable overclocks at 290MHz cpu host frequency. That means my RAM is running at 590MHz on a 2.0 memory multiplier setting.

Screenshot of CPUZ is available here: http://img178.imageshack.us/my.php?image=cpuzof3.jpg
April 24, 2008 2:00:03 AM

3.0 would need 428FSB thats pretty insane for your chipset. You need to put Vcore at 1.5 to see what she can do. Yor Vcore is definately holding you back. I need 1.2875 for 300FSB on my e2180 and on the other computer I got with e2180 it needs 1.4 for 3.0 same ram, same mobo.

Your lad probably had a P35 chipset or x38 chipset.

If you dont up VCORE your not gonna get any more.

When you want to OC "BIG" it is always a good idea to get a motherboard that runs a higher FSB then your CPU. 1066FSB mobo with a 1066FSB CPU aint gonna pull impressive numbers.
April 24, 2008 3:55:39 AM

Ahh, ok then. 1.5V for Vcore seems pretty huge, but I'll give it a go, and I'll keep in mind not to buy crap motherboards next time -.-

I've heard that you shouldn't got past 1.45V for this CPU though, or is that just a precautionary warning?
April 24, 2008 4:07:08 AM

It says right on the box it can go 1.5, just watch the temps. 1.5 should get you a few more clicks but be sure once you find your FSB limit to lower the vcore to the lowest voltage it will run stable.
April 24, 2008 4:28:34 AM

Unfortunately, upping the Vcore to those voltages does absolutely nothing. I tried it just then. The _only_ thing at the moment allowing me to overclock is upping the PCI-E bus = (cpu host frequency / 3) - 1 (or 2)

Maybe I have a dud board.
April 24, 2008 4:39:03 AM

You have a dud board and a dud CPU. CPUs with 7x multis just dont Oclock well.

Everyone is turned off by the new q9450 because its 8x multi vs q6600 9x, and q6700 10x.

Whats the max oc you fill safe with now? How high can you get it?
April 24, 2008 8:03:24 AM

Best stable overclock so far:
CPU Host Frequency: 340MHz
PCI-E Bus Frequency: 115MHz
Memory Multiplier: 2.0
Vcore: 1.25V
VDimm: +0.1V

Running prime95 to give it a stability check.
April 24, 2008 8:08:36 AM

So 2.38, like I said before you'll be lucky to hit 2.4.

I would take that stimulus tax rebate next month and get a new mobo cpu if I were you.

Get a mobo with a 1600FSB native built in and if you dont need a quad grab the e7200 that should be out next month. It should OC to the 4Gish mark on a good mobo and good cooling.
April 24, 2008 8:42:58 AM

I think you're right roadrunner.

I guess I'll end up getting a new computer out of all of this, so it should all be good :D . Here's to hoping I didn't waste all that money on cooling.

But I must say, thanks for all the help.
!