So, the Intel Xeon processor 5500 series can support both RDIMMs and UDIMMs, what about the motherboard?
The Intel X58 chipset, which is used on X8SAX and C7X58, supports DDR3 UDIMMs only. Therefore, the X8SAX and C7X58 support Core i7 processors (Bloomfield), Xeon processor W3500 series (Bloomfield), and Xeon processor 5500 series (Nehalem-EP), but only with DDR3 UDIMMs only.