Stupid (I think) FSB question

[Twofan]

I don't think I have ever seen this answered anywhere so I gotta ask. If you reach 166mhz fsb does the agp and pci busses revert back to normal, like all other 33mhz steps do? And does the ram run at the 166 speed. I have PC-166 ram and was thinking of trying 9.5@166 but don't want to get the pci buss too high. I have had some bad times splattering data at excessive pci speeds and really don't want to do it again. Much too hard to get this VIA board running right to be doing unnecessary F-Bombs.

[BrunoPuntzJones]

me wants to know also.

[castle lager fan]

In a normal mobo and chipset config the following is true.

The FSB is the I/O of your CPU which is directly connected to the northbridge(NB) of your chipset. The NB is then connected to the memory, agp and south bridge(SB). The disk controllers, PCI slots, USB, etc is connected to the SB.

The ratio between the FSB clock and mem clock is normally 1:1 and they are in sync, that why its called syncronous dynamic random access memory SDRAM. (On some chipsets this can be changes, but it does not make sense as it will affect you performance badly to change this. Also memory and FSB used to transfer data only on the up cycle of the clock, but with double data rate (DDR) stuff it transfers memory at both up and down cycles.) Your AGP is connected to your NB and runs at 66Mhz if my memory serves me correctly. AGP 1x runs at 33 MHz, AGP 2x at 66MHz and AGP 4x at 66MHz with double data rate. I need to look this up as I'm unsure. But back to the point there is a specific ratio between you FSB of your CPU and your AGP. This is normally variable between 1:2 or 2:3. Two CPU clock cycles per AGP cycle or 3 CPU for 2 AGP. This is to cater for 100MHz and 133 MHz CPU clock cycles. SOme motherboards you can set this, some sets it automatically according to the FSB speeds and AGP mode selected.

Now to the SB and PCI and IO. The bus between SB and NB runs at 33 MHz normally and is at a direct clock ratio from the CPU clock. 3:1 for 100 MHz FSB or 4:1 for 133 MHz. The devices hanging of the SB will clock at the bus speed.

So to your question. Unless your mobo has a setting to set all these clock dividors and multipliers for the different components, everything will go up at the specific ratios. Normally in your BIOS it will give you an indication of the ration between PCI and FSB clock. Normally where you set the FSB clock, you dont have to save the setting you can just look. I dont think your mobo will go to 5:1 for the PCI when you go up to 166 FSB. I dont think your mobo will take down the AGP clock either or the RAMN clock. WHen I refer to clcok I mean the clock timing of each component.

Look at you Iwill manual if it does not specify these settings you dont have it.

Hope this helps.

[supraway]

I'll sum that up. I don't think motherboards will do 5:1 ratio, unless bios allows changes. Highest, I believe, is 4:1. As for your memory, like he said, is synchronous, so it will run at 166. So you will be running your PCI at like 42 or so (too lazy to check) which is a little high.

[Twofan]

OK, thanks. Guess I will stay around 150 then. Can't complain about what I am getting now.

[Nagorak]

No it won't...stick to 150 MHz or so and you should be fine (PCI is only at 37.5 and AGP at 75). Going much beyond that and you're going to run into major problems...