PCI Speed and Overclocking: A Closer Look at A64 and P4 Chipsets
by Wesley Fink on February 16, 2004 9:42 AM EST- Posted in
- CPUs
PCI Speed and Overclocking: How We Tested
At stocks speeds and a x1 setting on the Geiger, the PCI bus is reported as 33.3MHz:
The shot above was actually taken on an Asus P4C800-E running at a 250 (1000FSB) setting. When PCI lock is working, the PCI bus stays around the default of 33.3. AGP speed is a 2X multiple of PCI in the most common setup.
When the PCI bus floats, or is unlocked, the PCI speed floats with FSB settings. You can see this here where the base FSB is set at 210:
The PCI is 1/6 the base setting of 210, or 35. This level of overclock is generally not a problem even when the PCI bus floats.
Raising the base FSB to 220, PCI increases to 36.6, or an unlocked AGP of 73.
This is often a problem for current AGP cards. Our ATI Radeon 9800 PRO tests cards generally fail in intensive benchmarking above an unlocked base setting of around 218-220.
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PrinceGaz - Monday, February 16, 2004 - link
I'm still awaiting any sort of reponse to the first post in this thread about why no tests seem to have been done at around 233 or 234FSB to see if a 1/7 divider kicks in. Thats the first thing I'd have tried after establishing no PCI lock at say 210 or 220. And yes, you can lower the multiplier on A64 chips so they aren't an issue like I said.Pumpkinierre - Monday, February 16, 2004 - link
Yes I second ionpro2's #13 suggestion. If you can get higher clockspeed by lowering the multiplier. try your geiger at these higher speeds and see what's going on.Icewind - Monday, February 16, 2004 - link
Now im curious as well as how you got it that highionpro2 - Monday, February 16, 2004 - link
Wesley Fink: No way that the motherboard would've posted with no PCI lock. Think about it: the devices that are dangling off of the PCI bus on the board itself would be running *way* the heck out of specification at the overclocks achieved on the Aopen. Perhaps these have higher tolerences, but I seriously doubt the ALC655 would run at 43Mhz, or the Realtek Gigabit LAN chip, either. Most likely, there are merely windowed dividers for these chips, with a 1/6 and 1/7 ratio. It would make sense for this to kick in at 220Mhz -- otherwise, you are running the PCI out of spec almost 10% down; and I'd be willing to bet whatever optimization is done for aftermarket cards is done for higher PCI/AGP speeds, not lower. *Please* test the AOpen board at 9x240 and see what PCI speed is reported.Wesley Fink - Monday, February 16, 2004 - link
Pumpkinierre -Your question is exactly the reason I stated that I don't know what is happening with AGP on A64 boards. With no PCI cards in my test setup, a working AGP lock could provide quite a bit of OC room. Some sites have reported AGP IS fixed on VIA, but I have no way of testing that. I can tell you for a fact that the PCI slots are not frequency locked on the A64 boards I tested, but the way frequencies are derived in HT it IS possible AGP is locked on some A64 boards.
Pumpkinierre - Monday, February 16, 2004 - link
I dont understand. You got 253MHzx8 and 240x9 on the Aopen A64 mobo when you tested it. That's a lot more than 220MHz. Even if the AGP was asynchronous, which I very much doubt, surely other components on the M'board would have seized?!impar - Monday, February 16, 2004 - link
I would like to see the same test in nForce2 boards...Icewind - Monday, February 16, 2004 - link
Sorry, guess I missed the defination of "go pound salt" so i'll take it with a grain of salt.idgaf13 - Monday, February 16, 2004 - link
If all The motherboard chipset suppliersdo the same thing ,such as the PCI lock,
musi be a "deeper"reasoning.
Certainly if possible ,contractually or technically, they would do it.
They all need that special selling point ,A point of differintation.
Basically "go pound salt" ,Icewind.
Icewind - Monday, February 16, 2004 - link
Cause VIA knows better and they still won't comply with the wishes of system builders. For that, I dispute them.