"One of the limits of the KX133 chipset is its failure to run correctly with the Slot A Athlon Thunderbird. Most users report no problems until you start reaching the 800mhz mark on the KX133. This was the case in our testing. The TBird would not even post at 850. The same TBird posted at 1ghz! in a AMD based MSI K7Pro"
FULL STORY @ VIAHARDWARE (http://www.viahardware.com/tekramk7.htm)