Server memory Udimm and RDIMM differences

Udimm

The full name is the Unbuffered dual-Channel memory module (unbuffered Dual in-lne memories Modules), which does not support server memory is fully equipped, is the highest capacity, because the maximum use of UDIMM memory per channel only 2 slots, but support 3 channels, So only 6 on each side, a total of 12 memory, can not be filled with 18 slots, although performance will be reduced, but for the budget more limited users, is a good solution.

RDIMM

Dual-channel Memory module with register (registered Dual in-lne Memories Modules), which indicates that the address and control signals of the controller output are output to the DRAM chip after register chip storage, The controller outputs a clock signal that passes through the PLL and reaches each DRAM chip. Compared to the UDIMM because of the register, so the processing speed of all aspects of performance has a lot of improvement, there are 2 modes of operation, that is, registered mode (register mode) and buffered (buffer mode) mode. When working on a motherboard that supports registered mode of operation, registered memory works in registered mode, when the address signal and control signal on the motherboard reaches the DIMM at the first clock cycle of the data signal. A clock cycle is placed on the register chip and then the rising edge of the next clock signal is output from the register, along with the data signal that arrives at the DIMM from the motherboard at the same time to the SDRAM. When the registered memory work on the common motherboard, for the buffered mode of operation, then all the signal is basically at the same time to reach the DIMM at the same time, register chip in the function is only a simple buffer, its input to the output is direct, Only simple to improve the address signal and control signal to the SDRAM, time series and unbuffered memory is the same. (typically used for servers) is suitable for different motherboards, and the RDIMM supports the highest configuration and is not limited by the number of memory plugs.

To summarize :

The RDIMM supports two modes of operation, supporting high-performance registered DIMM operating modes, which can achieve maximum memory capacity and higher prices.

Udimm can only work in unbuffered mode, unable to achieve the highest memory, performance is inferior to RDIMM, but the price is relatively low.

To illustrate:

Memory interpolation here is to say, because the server is often more than one CPU, so memory interpolation to pay attention to the dual CPU server as an example, the left and right 2 sides have memory slots, they belong to a CPU, so each CPU can only be divided into 72GB of memory, that is, 9*8, plug memory to be symmetrical, Try to avoid 5,7, this kind of interpolation, because the memory supports 3 channels, so can be 3 per side, or continue the dual Channel 2 can also, but 5 distribution uneven, start not, 7 is also the case.

Server memory Udimm and RDIMM differences