The difference between server memory Udimm and RDIMM

The Intel 5500 series Xeon CPU2009 year March launches, everybody in for this series CPU chooses the motherboard to be possible to see the memory support option generally is 2 kinds, one is supports 48G, one kind is 24G, the same server board how can be two kinds of different capacity memory support? The secret is in memory type one is Rdimm, one is Udimm.

Then what is Rdimm? What is Udimm?

Rdimm:registered DIMM (registered Dual in-line Memory module), dual-line memory module with registers. Indicates that the controller output address and control signal after reg storage output to the DRAM chip, the controller output clock signal after the PLL to reach each DRAM chip. Registered memory itself has two modes of operation, namely registered mode and buffered mode. When working on a motherboard that supports registered working mode, the registered memory works in registered mode, and the address signal and control signal on the motherboard will arrive at the DIMM in a clock cycle before the data signal is sent to The register chip will then stay in one of the clock cycles, then in the next clock signal rise along the register output, and at this time from the motherboard to the DIMM from the data signal at the same time transmission to the SDRAM. When registered memory is working on an ordinary motherboard for buffered mode, all signals are also basically reaching the DIMM at the same time to the Sdram,register chip, which is functionally equivalent to a simple buffer. The input to the output is straight through, only simple to improve the address signal and control signal function, timing and unbuffered memory is the same. Compared to Udimm due to have a register, so RDIMM processing speed in all aspects of performance have a lot of upgrade, there are 2 working modes, suitable for different motherboards, and RDIMM support the highest configuration, will not be limited by the number of memory plug. (General for servers)

UDIMM: No buffered Dual Channel memory module (unbuffered Dual in-line Memory modules,udimm). (commonly used for commercial purposes), UDIMM indicates that the address of the controller output and the control signal is reached directly on the DIMM's DRAM chip. It does not support server memory full, is the highest capacity, because the maximum use of UDIMM memory can only use 2 slots per channel, but support 3 channels, so you can only insert 6 per edge, a total of 12 memory, can not be filled with 18 slots, although performance will be reduced, but for a limited budget users, It's a good plan.

To sum up:

RDIMM supports two modes of operation, supports high-performance registered DIMM mode, can achieve maximum memory capacity and high price.

Udimm can only work in the unbuffered mode, can not achieve the maximum memory, performance is inferior to RDIMM, but the price is relatively low.

An example is provided:

Memory interpolation here to say that, because the server's CPU often more than one, so the memory interpolation should pay attention to

For example, Dell server R710 with dual CPUs, 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 the memory to be symmetrical, try to avoid 5,7, this kind of interpolation, because the memory support 3 channels, so you can 3 per side, or continue to double Channel 2 can also, but 5 distribution uneven, cannot start, 7 is also the case.