Can Someone Explain PCIe Speed Locking

[XStroX]

Hi All,

I just finished building my Pentium 805 D system and would like to overclock it a bit. I also have a PCI express Radeon X1300. I believe I've seen people mentioning that if you increase the FSB, that the speed to your PCI Express goes up as well and that theres no way to lock the PCI Express speed in at 100mhz or 133mhz (whatever it is I'm not sure) Is this something I need to worry about or does that not even make any sense? Thanks

Stro

 

[rwpritchett]

Yes, if your mobo has the option, you should lock the PCIe to 100MHz and the PCI to 33MHz. This increases stability when overclocking via FSB.

 

[XStroX]

If my mobo doesn't have the option then is there a certain limit I should stay under? If I up the FSB 20mhz, does that mean my PCIe will be 120 mhz? Thanks

Stro

 

[rwpritchett]

I'm not an experienced overclocker, but I'm very sure that the PCIe and PCI frequencies do not increase directly 1:1 with the FSB, it's most likely a ratio. For example if you OC to 300MHz FSB your PCIe might go to 112MHz (just an example that I pulled out of my a$$,) but I could be wrong.

The true limit for overclocking is determined by stability. If you have a video card that isn't sensitive to an OC PCIe bus and you don't have anything on the PCI bus that's likewise sensitive, then you can OC higher.

Basically, your OC will be limited by the most OC sensitive part in your system. It could be RAM, PCIe, PCI, etc. Locking down the frequency for a certain bus eliminates that part from the equation.

Just OC little by little until the system becomes unstable (or smoke starts coming out) and then back it off a little. Then you will know your limits.

 

[Aragorn]

If your system does not have an option to lock the PCIE bus then it may not allow it to move. On my Mobo no matter what I set my FSB to my PCIe speed doesn't move. If your PCIe bus speed changes with the FSB then the multiplier will be the ratio between the base FSB and 100 MHz. Since you have an 805 your base FSB is probably 200 MHz so your ratio is 1:2. If you raise it to 240 MHz then you will raise the PCIe to 120 MHz. If you only raise the FSB to 220 MHz then you only raise the PCIe to 110 MHz

 

[XStroX]

Thank you all for the response. I'm going to try and do some overclocking tonight now that the extra long weekend is over with.

Stro