VIA's KT133A - Overclocking w/ the 133MHz FSB: The "Issue"

Final Words

There is no doubt that the VIA KT133A chipset gives us a lot more flexibility in overclocking thanks to a much wider range of functional FSB speeds. And of course, the performance benefits of the 133MHz FSB cannot be ignored - you get near DDR performance without the need for new memory modules. Unfortunately, all too many motherboards have a problem with overclocking a CPU by lowering the multiplier and simultaneously increasing the FSB, which is exactly what we all want to do to take advantage of the 133MHz FSB of the KT133A.  The issue seems to come up on boards that have the multiplier in the BIOS but FSB in jumpers/dipswitches.  It also seems to be related to the fact that during the initial boot up, before BIOS settings are loaded, the system looks at the default values to initialize the CPU.  That boot up sequence totally defeats the attempt to overclock a 100MHz Athlon/Duron by lowering the clock multiplier and raising the FSB to 133MHz (or higher).

Luckily there are still workarounds for the problem.  They range from choosing a motherboard that features a fully jumperless or fully jumpered design to actually modifying your chip to obtain a lower multiplier.  Even with the most tedious possibility of modifying the chip, it’s not as hard as what you may expect.  In most cases, it is nothing more than adding a few bridges to the chip and, in the worst case, you will have to cut a bridge.

Hopefully this guide gives you a clear explanation of what happened and also the corresponding solutions.  As always, great care must be taken when overclocking in general, with extra care taken when modifying any of the bridges on the chip

Last of all, we would like to acknowledge VIA, ABIT, and Iwill for providing us with much of this information, as well as DaddyG from the AnandTech Forums for some of the details on multiplier settings.