I'm not serious enough to join a forum for this, but thought I would give it a go. The m/b i'm using provides an o/c utility so I shouldn't go too far wrong and i'm keeping an eye on the temp.

What confuses me is that when I o/c by 10%, the graphics card (7900GT) gives a poorer performance.

Any ideas?

It could be the pci/e bus is set to auto and is being set to lower than 66/100mhz. Try setting it manually.

Personally I can't stand clockgens and always set things up in the the bios.

Gilly, how you overclock will depend on which platform you're on. AMD or Intel? Also, what Shrick said: there's a feature called AGP/PCIe / PCI lock where you can lock the speeds of the PCI busses independantly of what the CPU clock is doing. If that's not activated / available, when you raise the CPU clock, the PCI / AGP busses may "slow down" so the numbers remain multiples of each other.

It could be the pci/e bus is set to auto and is being set to lower than 66/100mhz. Try setting it manually.

Personally I can't stand clockgens and always set things up in the the bios.

If it PCIe this won't be the case as the PCIe bus isn't clocked as such.

The PCI-e 1.0a bus will always run at 2.5GBit/s throughput rate per lane.

If it is AGP then that could be having a effect.

What are you O/Clocking? Is it the graphics card or the CPU/RAM.

If it is the graphics card, then what you could be doing is make the RAM run faster and DDR2/3 can have a very high first time latency, so you may be hitting that which makes things slower as the this is sat idle while it waits for the reply from RAM. The same could be said if your graphics card is trying to access system during it's latent period.

If it PCIe this won't be the case as the PCIe bus isn't clocked as such.

The PCI-e 1.0a bus will always run at 2.5GBit/s throughput rate per lane.

If it is AGP then that could be having a effect.

What are you O/Clocking? Is it the graphics card or the CPU/RAM.

If it is the graphics card, then what you could be doing is make the RAM run faster and DDR2/3 can have a very high first time latency, so you may be hitting that which makes things slower as the this is sat idle while it waits for the reply from RAM. The same could be said if your graphics card is trying to access system during it's latent period.

No the pci-e bus isn't clocked as such but you generally can alter the input frequency. Which would in turn effect anything else running off the SB, sata controllers etc.

Another thing to bear in mind is most motherboards (my Asus A8N included) will screw around with other settings unless you set everything to manual.. eg if i wind up the fsb, itll relax the the timings of the ram, and pull the multipliar and htt down on its own..

IIRC your running a athlon 64 setup?

Make sure you fix your HTT too, - it needs to stay around 1000..

ive got mine fixed at 4x at the mo and running at 11x250.. which is a healthy 2.75gig for the cpu, and the mem is running at FSB/14 which is about 196mhz but with nice tight timings... the system will run at over 3gig, but im happy with it at this level as cool n quiet works.

the best way to overclock is to do it in stages to see where your limits are.. eg back well off your RAM and just clock the cpu to give an idea where its limits are, then do the same with the ram.. then find a nice balance

If the motherboard manufacturer has implemented the standard, then PCIe should not be affected as the data is only fed in at a certain rate, with a limited message size specific header etc.

No the pci-e bus isn't clocked as such but you generally can alter the input frequency. Which would in turn effect anything else running off the SB, sata controllers etc.

PCIe isn't necessarily off the south bridge, in fact the ones for graphics are usually off the north bridge and it is used for a lot more than just expansion cards.

I am quite sure it won't be the PCIe bus that is the problem.

I think we need to know exactly which motherboard Gilly has

I agree this is probably not the problem, more info is really needed...

If it's an A64 there is as i'm sure you know no northbridge. Alot of enthusiast motherboards do like I said allow you to change the input frequency from the original 100mhz devisor, setting this to low can result in instability strangely, a slight increase can actually help with stability when overclocking, over 120mhz generally results in sata data corruption.

Anyway I think we've strayed far enough off topic...

Gilly what components are you using? What exactly are you overclocking? What are you using to test for stability?

Cheers

What you say is correct, but PCIe will not be effected by this as the link either works or doesn't.

I agree however, far enough off topic.

The spec is as follows:-

A8V-VM Motherboard

AMD x2 4800 CPU

2 x 1Gb Corsair DDR 400 3200C2PT RAM

XFX 7900GT PCi-E GPU

Hitachi Deskstar HDD

Windows XP Pro

I have so far only clocked the CPU. I have an Nvidia prog to clock the GPU but haven't used it properly yet.

I have sensorsview pro3.1 to keep an eye on temps and am running 3DMark06, PCMark05, Performance Test and Burn in Test.

Thanks,

Jon.

You asked da question, now you dissing me man.

:bump:

Sorry about that. What was the question again?

TBH, no idea why your perf drops. Could it be the o'clocking software is based on reference 7900 speeds and not GT or speeds specific to your card which may be already "factory overclocked above 10%"? So when you o'**** 10%, you're in fact running slower than the original speed.

Other than that, I've never bothered o'clocking. Until you get to silly details, it tends to be the CPU that's the bottleneck. I've just upgraded to a 7950 and my single core A64 running at 2.5GHz is fast enough for anything my 20" TFT can take (1600x1200).

I have a DC A64 running at about 2.5GHz on my media PC which is connected to the projector running at 1920x1200 and that looks rather sweet too

Gilly,

What are the multipliers you are using for the CPU and what are the FSB (or equivalent) speeds that you are running at?

If you over clock your FSB (or hyper transport bus in this case) your system RAM will have to be able to cope with this.

HTH