1.8a & p4b266-C Overclock Question

[Dre]

I have an Asus P4B266-C Mobo and a 1.8a. If I have the FSB set to 125mhz, what does my AGP/PCI clocks run at? How do you figure this out?

 

[WarCon]

I believe your PCI would be at 41.67mhz if you use normal. If you use turbo1, I think it locks at around 37mhz.

............edit...........
Some motherboards will kick in the 1/4 divider before 133, but I have no idea if this one does because there isn't any settings to adjust it manually. Oh and you take your fsb/3 before 133fsb then it goes to 1/4 and I believe some boards even have a 1/5 divider for 166fsb.

 

[Dre]

Regarding the use of the turbo1, turbo2 options, I really have no faith in that actually working. Only 1 person has ever said they actually tested it and it was someone by the name of "ase" on Hardforum who had 8 posts total under his name. Check out this post:

Overclockers Forum


Basically I'm in agreement with these guys that the turbo1 and 2 options are probably just some memory optimizations.


Back to my original question, can someone tell me what my pci/agp clocks are at when my fsb is set to 125mhz and I'm using "normal mode"? Also, if you could explain how you figure out the pci/agp speeds at various fsb's, that would be great. thanks in advance.

 

[Dre]

Just to followup, here is the original post at Hardforum where the whole idea that the turbo1 option locks the pci/agp clock.

Hardforum Post


Ase's post is towards the end of the thread. I for one, like to get my information from more credible sources before I consider it a fact.

 

[WarCon]

Short of measuring it yourself, Asus hasn't provided any clue. If you get "proof" please let us know.

But I described above how the frequency dividers go for a typical system. I really honestly have no idea how this board actually adjusts the PCI/AGP bus. Oh and the AGP bus is always twice the PCI bus.

 

[Dre]

Warcon
Thank for the followup. I hate the fact that the documentation for this mobo is vague on some things. I guess what I could always do if I wanted to be sure is use the dip switches. At least for the dip swtiches, Asus documented in the manual what speed your pci/agp clocks would run at with different settings. Here are some of the settings I can run at using the switches:

FSB: 120mhz
PCI: 40mhz
AGP: 80mhz

CPU: 120mhz
PCI: 30mhz
AGP: 60mhz

CPU: 125mhz
PCI: 31 mhz
AGP: 62 mhz

CPU: 133 mhz
PCI: 33 mhz
AGP: 66 mhz


Looking at these settings, it would seem that if you use the BIOS to set 125mhz FSB, your PCI and AGP would have a 1/4 divider. The reason I assume this, is because there is no other divider when using the dip switches and 125mhz.

Also, when you run 120mhz FSB with dip switches, you have the choice of either a 1/3 or 1/4 divider for the AGP/PCI clock. When using the BIOS, as far as I know you have no option of specifying what divider to use for the PCI/AGP clocks so I have no idea what they would run at using the BIOS.