Oc'ing Hurts Performance...

[lynx]

Very often, the pci and agp bus speeds are a division of the FSB clock.

So for instance if the nominal FSB speed is 133MHz, the pci speed would be FSB/4 (22MHz) and the agp speed would be FSB/2 (66MHz). If the FSB speed is increased to 150MHz, this would change the pci speed to 37.5MHz and agp speed to 75MHz. This can be enough to cause numerous faults on pci and agp buses, and consequently cause instability. This is often called the southbridge multiplier.

Often the memory speed is linked to the FSB speed too, this is called the Northbridge multiplier.

Some motherboards have the ability to use a separate clock for the Northbridge and Southbridge speeds, which is useful in determining maximum stable processor speeds, but the result is that memory and peripheral transfers are out of sync with the processor, which reduces performance slightly, but as we have seen from 3GN's posts the end result is still better than standard.

And while this is usually done in bios settings, motherboard manufacturers often supply software to adjust FSB and multiplier speeds 'on the fly', which can be extremely useful for testing system stability - if the settings have been locked into the bios, and the system won't boot because the speed is too high, the only solution is to clear the cmos and start again, and hope you can remember what all the settings were.

[bigdawgfoxx]

ok thanx that helped a lot....but whyd you use 133..arent FSB at 800Mhz now? ...so would the PCI be 200mhz and the AGP 400 mhz? or is 133 not the fsb? a lil confused on that one...but thanx...would you just set the agp and pci to stay at 66 and 22mhz and just raise the CPU clock?

[lynx]

It was just an example.
If the FSB clock was 200MHz then default agp would be FSB/3 (still 66) and default pci would be FSB/6 (still 33)

Note, FSB800 is actually 200MHz with a 4x pre-multiplier, confusing isn't it.

That's why it is important to look at base clock speeds rather than quoted rates, because of the multipliers/dividers involved.

If you have the ability to lock the agp and pci (and preferably memory too) it is a good idea to do so initially, to establish the maximum speed the processor is capable of sustaining. But it is also a good idea to find out the maximum speeds you can run the other devices at without exceeding the processor capabilities, and get the best of everything.

For example, if you determine that your processor becomes unstable at 1880 MHz (188x10), and the maximum speed for your agp/pci (with dividers) is 144MHz, you could set the fsb clock to 144MHz and the multiplier to 13, giving 1872MHz (a tiny drop in cpu speed) which would bring everything back into line and synchronise the north and south bridges with the cpu.

[bigdawgfoxx]

oh...so do the agp and pci have to be set the same? and how do you know how to do FSB\4 or FSB\3...and what is the 200Mhz multiple of 4? what is the multiple of 4?

[3rd gen noob]

lynx just reminded me about this topic two minutes ago in another topic, i had forgotten about it
well, he's up over 6000 now, the new drivers for video card seem to have done the trick...he's also getting approx 5800 just on the cpu overclock, so he's happy with that...
i don't have any ss's for proof just now, but i'll put them up when i get them

[abu_has_the_power]

how do u lock down the agp to 66mhz?

[3rd gen noob]

Originally posted by abu_has_the_power@8 October 2003 - 00:50
how do u lock down the agp to 66mhz?

look in your bios...you should be able to find an option in there

[3RA1N1AC]

Originally posted by 3rd gen noob+7 October 2003 - 16:51--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (3rd gen noob @ 7 October 2003 - 16:51)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-abu_has_the_power@8 October 2003 - 00:50
how do u lock down the agp to 66mhz?

look in your bios...you should be able to find an option in there [/b][/quote]
also depends on which motherboard you own. locking the AGP/PCI/RAM bus speeds is a pretty new feature... up till a certain period, motherboards just couldn&#39;t do that at all so overclocking the FSB would screw up all sorts of things. hurrah for progress.

[abu_has_the_power]

under wat category. i looked and didn&#39;t find much

[3rd gen noob]

Originally posted by abu_has_the_power@8 October 2003 - 01:27
under wat category. i looked and didn&#39;t find much

it&#39;ll depend on your motherboard (or bios)
for example, i believe mine is in advanced chipset features, though i&#39;m not sure...