Server terminology: RDIMM, UDIMM

Intel 5500 series Xeon CPU was launched in March 2009. When you buy a motherboard for this series of CPUs, you should be able to see that the memory support options are generally 2, one is to support 48G, One is 24G. How can the same server motherboard be supported by two different capacities? The secret is in the memory type, one is RDIMM and the other is UDIMM.

So what is RDIMM? What is UDIMM?

RDIMM is a Registered DIMM, which means that the address and control signal output by the controller are registered by Reg to be output to the DRAM chip. The clock signal output by the controller passes through the PLL and reaches each DRAM chip. A UDIMM, an Unbuffered DIMM, indicates that the address and control signals output by the controller directly reach the DRAM chip on the DIMM.

RDIMM: Registered DIMM (Registered Dual In-line Memory Module), a two-wire memory module with registers. Registered memory itself has two working modes, Registered mode and Buffered mode. When working on a motherboard that supports the Registered mode of operation, Registered memory works in Registered mode. At this time, the address signal and control signal on the motherboard will arrive at the DIMM one clock cycle before the data signal. After the Register chip is sent, it will stay in the clock. The cycle is then output from the Register on the rising edge of the next clock signal, and simultaneously transmitted to the SDRAM along with the data signal arriving from the motherboard to the DIMM at this time. When the Registered memory works on a normal motherboard, it is in Buffered mode. At this time, all the signals are basically simultaneously reached to the DIMM and then transferred to the SDRAM. The Register chip is functionally equivalent to a simple Buffer. The input to the output is straight-through, and it simply functions to improve the address signal and the control signal. The timing is the same as Unbuffered memory. (Generally used for servers)

UDIMM: Unbuffered Dual In-Line Memory Modules (UDIMM). (Generally used memory modules for general commercial use)