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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gordon151 - Monday, February 16, 2004 - link
All the chipsets for the A64 don't have PCI locks, why are you singling out VIA Icewind???Wonga - Monday, February 16, 2004 - link
I think it is a bit pathetic how none of the chipsets for the Athlon 64 can manage to get a working PCI lock in them.Come on SIS/VIA/nVidia, you can do better than that. How they can do it for the Pentium 4 but screw up on the Athlon 64 is pathetic.
Icewind - Monday, February 16, 2004 - link
The first SATA did rely on the PCI bridge but the newer ones have their own dedicated bus to the southbridge so it is not affected by OC. ATA is still attached to the PCI bus if I remember correctly.lebe0024 - Monday, February 16, 2004 - link
What about harddrive controlers? Does SATA depend on the PCI bus? how about PATA?Icewind - Monday, February 16, 2004 - link
Cool, no wonder my P4C800-E Deluxe is such a kick ass overclocker. Another reason why not to buy VIA chipset mobo's. Lets hope Nvidia can make a good 939 pin mobo later this year, VIA still leaves a bad taste in my mouthPrinceGaz - Monday, February 16, 2004 - link
Would it have been possible to raise the FSB to 233 or 234 on those A64 chipsets to see if a 1/7 divider kicks in? I believe the A64 is partially multiplier-unlocked and can have it lowered because of the Cool n Quiet power-saving technology so the CPU itself shouldn't have been a problem.If current 8x AGP cards are so sensitive to AGP speed, why not use a slower AGP mode or use an older card which can tolerate a far wider range for some of the tests? I've got an old 2MX somewhere that was quite happy with a 75MHz AGP speed (150FSB on a KT266A chipset, equivalent to 225FSB on current boards) and may well have gone somewhat higher but my PC2100 memory couldn't take any more.
Interesting article though, surprising about the nForce3 board.