"The most noticeable feature of the layout is the option to use either SDR or DDR memory. Users can run memory in two SDR slots or three DDR slots, though one can't run DDR and SDR at the same time. This feature is common on a lot of first generation AP266 motherboards, which gives users the ability to reuse their PC100/133 memory and later upgrade to DDR. "
FULL STORY @ VIAHARDWARE (http://www.viahardware.com/pro266master.shtm)
