I'm muddled again! I want to upgrade from PC133 to PC2100.My mobo, ASRock K7VM2 gives the choice of 2 of either. I see some PC2100 on Ebay of 266Mhz, which I thought was the norm, another of 400Mhz. My manual says Chipset North Bridge: Via KM266, [email protected]/266MHz, AGP 4X. Clock Generator 100MHz-200MHz. This makes me think the 266ram would be OK. Any ideas, please? Thanks, Al.