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

Introduction

In the summer of 1999, AMD announced the original Athlon and has never looked back.  Besides just having a superior CPU, one of the reasons for their success, as most hardware enthusiasts have known, is the overclocking ability of the chips.  Shortly after the release of the Slot-A Athlon, the secret to modifying the clock multiplier was revealed and the famous Gold Finger Devices (GFD) started to appear on the market.

Fast forward to last year when AMD released the newly designed Socket-A Athlons and Durons.  VIA continued to supply chipsets for AMD’s latest and greatest processors with the KT133 chipset.  Initially, these new processors appeared to be completely multiplier locked, much like what Intel had done with their CPU’s. Fortunately, the secret of how to modify the clock multiplier on Socket-A chips was once again revealed, and motherboard manufacturers wasted no time in the rush to implement such a feature on their motherboards.

Unfortunately, one big downside of the VIA KT133 chipset was that overclocking the front side bus (FSB) was simply not effective since,  in most cases, it would not run any faster than 110MHz, a mere 10% overclock.  It initially appeared that this was a limit of the Athlon’s EV6 bus, possibly due to the fact that it transfers data on both the rising and falling edge of the clock signal, which effectively doubled its speed, just like DDR did for memory.

Nonetheless, in late December 2000, shortly after the release of the 266MHz Athlon, VIA finally came back with the “new” KT133A chipset, which is nothing more than the KT133 with official 133MHz support.  Many have suspected that VIA intentionally disabled faster FSB speeds in the KT133 because there were no Athlons that supported such high speeds.  This may even have been to appease AMD, although this is all just speculation.  Regardless, the KT133A and its 133MHz FSB provided much of the performance of the AMD 760 chipset, but without the need for new and costly DDR-SDRAM.  For overclockers, the KT133A promised to work with a much wider range of overclocked FSB speeds, sometimes as high as 160MHz or above.

The KT133A chipset soon became one of the most hotly discussed topics among hardware enthusiasts, with quite a few people jumping into the KT133A market as soon as boards became available.  With almost all motherboard manufacturers integrating the hardware setup for clock multiplier on their KT133A solutions, most of these people were hoping to gain near AMD 760/DDR-SDRAM levels of performance simply by overclocking their CPUs with a lower clock multiplier and higher FSB speed.

Unfortunately, the results didn’t come out as expected for everyone.  For many, it was simply not possible to get a 100MHz Athlon or Duron to boot at 133MHz FSB, regardless of the multiplier used.  Of course in theory, if you set the multiplier low enough, the FSB should not pose a problem and the overall speed of the CPU won’t even be overclocked. 

So what went wrong?  The concept is simple enough, but there seemed to be random failures all across the AnandTech community.  Was it chipset related or motherboard related?  And most importantly, are there any solutions for you, who may have already spent over $120 on a KT133A motherboard?  In this article we will address the issue as well as provide the corresponding solutions.

Before going into the details, we highly recommend you read the following articles.  The information contained within the listed articles is essential for you to understand the rest of this article.

AMD Thunderbird / Duron Investigation and Overclocking Discussion

AMD Thunderbird & Duron Overclocking Revealed

AMD Socket-A 133MHz FSB / DDR Overclocking Guide

Overclocking AMD’s Thunderbird and Duron Processor on Tom’s Hardware

Overclocking AMD’s Socket Processors on Tom’s Hardware