Reprinted from http://www.sohu.com/a/165343889_781333 .
DIMM Profile
DIMM (Dual Inline Memory Module, dual inline memory module) SIMM (single in-line memory module, the memory module contacts unilateral) quite similar, except that both ends of the DIMM not cheat is interconnected as SIMM are each independently a transmission signal, and therefore meet the need for more data transfer signal. Also uses the DIMM, DDR memory interface to the SDRAM interface is slightly different, as the DIMM SDRAM 168Pin DIMM configuration, finger on each side of 84Pin, there are two tabs on the finger, is inserted into the slot to avoid the time, the error reverse insertion may destroy the memory; DDR DIMM 184Pin DIMM configuration is used, each side has Goldfinger 92Pin, Goldfinger only a bayonet. Bayonet number of different, is both the most obvious difference. DDR2 DIMM is 240pin DIMM structure, each side has Goldfinger 120Pin, with Goldfinger DDR DIMM only as a bayonet, but the position of the bayonet DDR DIMM have some slightly different, so DDR memory is not inserted into the DDR2 DIMM , empathy DDR2 memory is not inserted into the DDR DIMM, so on some motherboards have both DDR DIMM and DDR2 DIMM, the problem will not occur memory plugged into the wrong slot.
Difference UDIMM, RDIMM, SODIMM and the LRDIMM
UDIMM, Unbuffered DIMM, located in the desktop market, refers to the address and control signals without a buffer, the timing did not make any adjustments (buffer delay is there), directly to the DRAM chip on the DIMM. Registered memory module and the address and control signals for storage, then the trigger output at the next clock comes.
RDIMM, Registered DIMM, located in the workstation and server markets, refers to address and control signals through the register, the clock through PLL lock. With respect UDIMM, RDIMM more stable, larger capacity, but for a single read and write access to one clock cycle hysteresis. Registered memory itself has two operating modes, namely mode and Registered Buffered mode. After work on the motherboard supports Registered mode of operation, operating in Registered Registered memory mode, when the address signal and a control signal to be on the motherboard DIMM reaches a clock cycle than the data signal, which is fed Register chip will stay a clock cycle, then the next rising edge of the clock signal output from Register, at that time reaching the DIMM data signals simultaneously transmitted together from the motherboard to the SDRAM. Registered memory when working on a common motherboard for Buffered operation mode, when all the signals are also substantially simultaneously arrive simultaneously to the SDRAM DIMM retransmitted, Register chip time corresponding to only a simple function Buffer in which between the input to output is straight through, simply acts to improve the address signal and the control signal, the timing of Unbuffered memory is the same. Registered DIMM and other memory compared to an increase of two key components, PLL and register.
SODIMM, Small Outline DIMM, located in the notebook market, UDIMM and RDIMM are subordinate DIMM, memory modules such as length, including signal distribution, including Goldfinger's all the same. The smaller size can be understood as SODIMM memory modules.
LRDIMM, Load-Reduced DIMM, without the use of complex registers, but the use of a simple buffer. Buffering reduces the power load on the lower layer of the motherboard, but almost no effect on the energy and memory performance. Not like RDIMM and LRDIMM allow server manufacturers to put more modules on each memory channel. Therefore, LRDIMM designed to contain large volumes of system memory, without generating high costs of delay.