Calculating PCI bus speed from FSB

[andycheah]

Hello,

I was just wondering how to calculate PCI bus speed from FSB...

Right now I'm running an ECS K7S5A with 143 FSB. Since dividing 133 FSB by 4 gives the official 33 MHz, I'm guessing that I would divide 143 by 4 to get my PCI bus speed of 35.75 MHz. Is that correct? If so, is this safe to do?

Thanks in advance for any replies,

Andy

 

[RalfHutter]

Yes, that's correct if you're running a 4:1 divider. There's no software-based way to tell exactly what speed your PCI/AGP is running at so you have to trust what (if anything) your BIOS is telling you about your dividers. You can use an occilliscope or a PC Geiger to see your actual bus speed. There also may be people out there who know about the K7S5A and can tell you for sure what dividers there are for this board.

 

[Lord Evermore]

It only supports 100/133MHz bus Athlons officially, so the only dividers are 3 up to 132MHz (presumably) and 4 after that.

That PC Geiger also appears to be becoming outdated. It says it shows PCI speeds at dividers of 1, 2, 3 or 4. So a 166MHz or 200MHz bus system using proper dividers may not work. Or systems which simply lock the bus speeds independently of the FSB may not work. Or it may not really matter what the dividers are and the specs may just mention that to indicate that it works no matter what the divider is. Presumably it's directly accessing the PCI bus to find out what frequency it is, so the dividers shouldn't matter.