the athlonc is an athlon that id factory rated to run on the new 133 mhz fsb. which is only available on mainboards that have the via kt133a chipset or one of the new ddr chipset boards.
doesn't appear to have to be an athlonc just a kt133a chipset to reach close to 166 fsb
<A HREF="http://www.overclockers.com/articles325/" target="_new">http://www.overclockers.com/articles325/</A>