Confused by BIOS Limits

[ksonnad]

I recently acquired a Soyo SY-KT400, a Thoroughbred Athlon XP 2600+, and 1.5GB or PC2700 RAM. As it's a bit obsolete at this point, I thought this was a good time to get into overclocking and squeeze as much power out of it as I could. But I'm slightly confused.

According to Soyo, my motherboard only supports FSB speeds up to 333MHz (166). Yet in the BIOS, I have the option of increasing the CPU FSB up to 505MHz (255) and the DRAM Clock up to 400MHz (200).

Any attempt to actually do so causes a refusal to post or a "stop error" (don't know what that is) and I can't fully boot.

Am I out of luck and limited by the motherboard? If so, why does it have the option to go beyond it's limits?

Or am I doing something wrong?

 

[myocardia]

First, this BIOS limitation you mention has nothing to do with your FSB, only which Athlon XP processors the board supports. So, you can't use a Barton in it, only a Thoroughbred or older core. And the reason you aren't able to make it to Windows once you jack up the FSB is because you're jacking up the FSB. Raise it by a few Mhz at a time, and your "luck" will change.

 

[ksonnad]

Thanks for clearing that up. Now that I know I can OC it, I'm a lot happier.

However, I should have been clearer. I have not attempted to OC to the maximum values, only in modest increments of 10 MHz. Unfortunately, the BIOS defaults the DRAM clock to 166 whenever I set the CPU to 166 or more, and there's no DRAM divider. The BIOS warned me against setting the FSB higher than the DRAM clock. I tried it once, and got that "stop error." So I can't up the FSB, and the CPU multiplier's already at the max, too. Is there any way around this?

 

[ksonnad]

It appears that the VIA KT400 Chipset is inherently limited when interfaced with a 166/333 FSB CPU--it will always default the memory to 166/333.

I suppose I could up the CPU to 200/400 and try to fool it, but it's unlikely to be stable at the speed, isn't it?

Any other ideas?

 

[nonameo]

Another part of the problem could be that your AGP/PCI may not be locked. I don't think that really started to come into vogue until the nforce2 chipset came.

 

[Patrese]

Originally posted by: nonameo
Another part of the problem could be that your AGP/PCI may not be locked. I don't think that really started to come into vogue until the nforce2 chipset came.

You've hit the nail in the head. VIA KT400 and even VIA KT600 are not PCI/AGP locked. On VIA chipsets, that feature appeared only on KT800. Overclocking AXP is a lot easier on NForce2 boards like my Abit AN7, or the king of overclock on its age, the Abit NF-S rev.2.

 

[ksonnad]

No, the AGP and PCI are not locked. However, there is a DRAM:AGPCI ratio which keeps the AGP/PCI bus within acceptable parameters.

EDIT: There's also a CPU/PCI Divider.

As for the KT400 chipset, I've seen several websites which claim to have overclocked the mobo beyond 166 FSB, but I don't know how they did it. I don't want to give up yet.

 

[VirtualLarry]

Originally posted by: ksonnad
No, the AGP and PCI are not locked. However, there is a DRAM:AGPCI ratio which keeps the AGP/PCI bus within acceptable parameters.

Only up to 333Mhz FSB speeds. There is no /6 divisor for 400Mhz operation.

Originally posted by: ksonnad
EDIT: There's also a CPU/PCI Divider.
As for the KT400 chipset, I've seen several websites which claim to have overclocked the mobo beyond 166 FSB, but I don't know how they did it. I don't want to give up yet.

The only hope that I can see is using an AGP card that is tolerant of higher than 66Mhz bus operation, and then using a PCI IDE card, that has it's own clock crystal, and can clock the IDE bus properly at 33Mhz, even with the PCI bus itself overlocked higher. Otherwise, you will corrupt your IDE HD at speeds higher than 33Mhz on the PCI/IDE busses.
I have an MSI KT400 board, and I run it at 333FSB, with PC2700 memory. Attempting to run at 400Mhz FSB is crazy, IMHO, because of the lack of proper divisors.