PCI speeds while overclocking FSB.

[Torghn]

Do the PCI bus speeds go up the same % you rais your FSB or is there another way of figuring out how fast your PCI slots will run at if you up the FSB? I have an old Socet 7 motherbord that normaly runs at 66Mhz, In the bios I can rais it to 83Mhz, this really helps the speed, but how fast will my PCI slots be running at? It's a 25% increas so will my PCI slots be running at 41Mhz? Is this too fast for most PCI cards? Also is there anything else on the motherbord that would cause problesm running faster (ie cash ect), The Ram and CPU will be fine as they are rated at 100Mhz.

 

[Boonesmi]

pci is a fraction of the fsb
on a 66mhz bus its set at 1/2
100mhz bus its 1/3
133mhz bus its 1/4

so on your 66mhz board if you set the fsb at 100mhz the pci will be 50mhz thats very very high most likely your pci cards/and hard drive(hard drive is on the pci bus) will have problems

 

[Torghn]

Ok, so at 83, they'll be running at 41.5Mhz Is that too hight or can most cards run at that? The computer is running at that right now, is their anyway I can stress test the PCI cards it to see if it will crash?

 

[Belegost]

Actually, it probably won't raise your PCI at all. On my ASUS P5A I can run 83mhz with 33mhz PCI.

 

[MCS]

Belegost - that is absolute nonsense!

 

[syadnom]

your problable going to run 66/33 or 100/33 but 83mhz is an odd FSB, a lot of boards wont support any other pci divider, your problably going to run @ 41.5mhz, which is OK for SOME cards but some wont like it, i used to have problems with hard disk controllers/nic cards/ and scsi controllers with this high of PCI. i would generally try to keep your PCI as close to spec, at least below about 37-38.

good luck

OH - MCS, there are boards that support 2.5 PCI dividers, they are ones that were made to support the 83mhz bus cyrix chips.

 

[Rand]

The speed of the PCI bus at an 83MHz FSB would depend upon your mottherboard and the PCI bus dividers it is capable of. In most cases an 83MHz FSB would utilize a PCI divider of 1/2 which would equate to a peed of 41.5MHz for the PCI bus frequency.

Unfortunately a 41.5MHz PCI bus is rather high and many cards may not operate properly at that speed. It's generally preferably to keep the PCI bus speed around or below 37-38MHz which is safe for the vast majority of cards.
Another issue is the fact that most IDE HDD's will not operate correctly at PCI bus frequency of 41.5MHz. Also, many SCSI cards are expecially sensitive to out of spec PCI speeds.

 

[Torghn]

Ok, well it's running now. If it starts locking up or I get problems I'll drop it to 75Mhz which will put the bus speed at 37.5 Mhz.