Yup, almost all SMP opteron boards are built using AMDs reference chipset, which doesn't provide PCI-E, only PCI-X, also the prices of SMP opteron boards are a little costlier than SMP Xeons and the registered RAM needed for opterons is also costlier. However, the cpu price is cheaper and you have the option of dual core and also great performance and 64-bitness Ofcourse, Nocona also has 64-bit support, but the performance is'nt too encouraging at this moment