3PCS 4GB 1333MHz ECC REGISTER Genuine CMS brand, CMS is one of the most trusted names in the Computer Memory industry and this product carries a Lifetime Warranty from CMS Compatible with: Dell Precision Workstation R5500 Maximum Memory: 48GB ECC UDIMMs 192GB Reg ECC RDIMMs Expansions: 6 Sockets per CPU 12 Sockets using two CPUs Note: DDR3-1333 modules automatically clock down to 1066MHz and 800MHz depending on which Intel Xeon model is installed and how many module banks are populated. Due to chipset limitations, DDR3 Quad Rank memory will operate at 1066MHz in the first Triple Channel bank. Adding Quad Rank modules in the second Triple Channel bank will operate at 800MHz. This system supports either Registered ECC or Unbuffered ECC memory. Mixing Registered ECC and Unbuffered ECC modules is not supported within this system. 4GB DDR3-1333 Reg ECC modules come in two versions: 313/4G using x4 and 3138/4G using x8 DRAM. The two parts may be installed in the same system but not within the same memory bank. Use like modules for dual and triple channel operation.