AGP/PCI CLOCK VALUE

[matermoh]

I have my AGP/PCI CLOCK locked at 66.66/33.33. I heard this is the best for video card performance, but wasn't sure exactly what it does. I was wondering if someone could explain agp/pci clock to me, and if this is the best setting for an overclocked system.

 

[So]

Originally posted by: matermoh
I have my AGP/PCI CLOCK locked at 66.66/33.33. I heard this is the best for video card performance, but wasn't sure exactly what it does. I was wondering if someone could explain agp/pci clock to me, and if this is the best setting for an overclocked system.

That is the speed that the busses run at. All agp and PCI cards are designed with the assumption that their bus will be running at that speed. Some cards can be run out of spec without problems more reliably than others. In the old days the system determined the clock of your AGP and PCI buses by dividing the FSB by a fixed ratio (say if you had a 133 mhz bus, 1/4 gets you 33mhz which is the speed of the PCI bus). I know that recently 'clock locks' have appeared that let you set and Front Side Bus at any speed and maintains the PCI and AGP clocks. This is a major improvement for overclockers who can now clock up their FSB with out fear of it causing problems for add in cards.

Simple answer: you always want your AGP bus to run as close to 66Mhz as possible and your PCI bus as close to 33Mhz as possible. Deviating from that will lead to instability, not performance gains.

 

[evilbix]

this is interesting.. when did they start locking them? i think that could be why I can't push 160fsb with my northwood b.

 

[matermoh]

Awesome! Thanks for the information. I'll be sure to pass it along.

 

[So]

Originally posted by: evilbix
this is interesting.. when did they start locking them? i think that could be why I can't push 160fsb with my northwood b.

No, they started 'locking' them around the nforce2 generation IIRC. But THIS IS NOT why you can't push your northwood faster. Decoupling the AGP/PCI busses (i.e. locking them) from the FSB if anything, allows you to overclock MORE because you don't have to worry about pushing the AGP/PCI buses out of spec, which used to be a major inhibitor for overclocking.