In the server field, there are three main types of memory modules (DIMMs) currently in use: UDIMM, RDIMM, and LRDIMM.
UDIMM
UDIMM: The full name is Unbuffered DIMM, that is, unbuffered dual in-line memory module, which means that the address and control signals are not buffered, without any timing adjustment, and directly reach the DRAM chip on the DIMM. Because UDIMM does not have any cache between the CPU and the memory, the delay is small at the same frequency.
When data is transmitted from the CPU to each memory particle, UDIMM needs to ensure that the transmission distance between the CPU and each memory particle is equal, so that parallel transmission is effective, and this requires a higher manufacturing process. Therefore, UDIMM has both capacity and frequency. Lower.
The difference between server UDIMM, LRDIMM, and RDIMM memory
RDIMM
RDIMM: Full name Registered DIMM, dual in-line memory module with register. RDIMM adds a register to the memory bar for transmission, which is located between the CPU and the memory particles, which not only reduces the distance of parallel transmission, but also ensures the effectiveness of parallel transmission. Due to the high register efficiency, the capacity and frequency of RDIMMs are easier to increase compared to UDIMMs.
The difference between server UDIMM, LRDIMM, and RDIMM memory
LRDIMM
LRDIMM: The full name is Load Reduced DIMM, a low-load dual in-line memory module. Compared with RDIMM, LRDIMM does not use complex registers, but simply buffers. The buffer reduces the electrical load on the lower motherboard, but it has almost no impact on memory performance.
In addition, LRDIMM memory changes the Register chip on RDIMM memory to iMB (isolation Memory Buffer) memory isolation buffer chip. The direct benefit is to reduce the memory bus load and further increase the memory support capacity.
Difference and application
Because UDIMM does not use registers, no buffering is required, and the delay is small at the same frequency. In addition, another advantage of UDIMM lies in its low price. The disadvantage is that the capacity and frequency are low, the capacity is up to 4GB, and the frequency is up to 2133 MT/s. In addition, because UDIMMs can only work in Unbuffered mode and do not support full server memory allocation (maximum capacity), server performance cannot be maximized. In application scenarios, UDIMM can be used not only in the server field, but also in the desktop market.
RDIMM supports Buffered mode and high-performance Registered mode, which is more stable than UDIMM, and supports the highest capacity of server memory. In addition, RDIMM supports higher capacity and frequency, the capacity supports 32GB, and the frequency supports 3200 MT/s. The disadvantage is that due to the use of registers, the delay is high, and the energy consumption is increased at the same time. In addition, the price is more expensive than UDIMM. Therefore, RDIMMs are mainly used in the server market.
LRDIMM can be said to be a substitute for RDIMM. On the one hand, it reduces the load and power consumption of the memory bus, and on the other hand, it provides the maximum support capacity of memory. Although its highest frequency is the same as RDIMM, both are 3200 MT/s, but Increased to 64GB in capacity. And, compared to RDIMM, Dual-Rank LRDIMM memory consumes only 50% of its power consumption. LRDIMM is also shipped in the server field, but its price is more expensive than RDIMM.
Uncached ECC DIMM (ECC UDIMM), Registered DIMM (RDIMM), and Load-reduced DIMM (LRDIMM)
Memory sticks are divided into Single-Rank, Dual-Rank, Quad-Rank according to the number of DRAMS, abbreviated as 1R, 2R and 4R respectively. Rank is the data usage area composed of a group of DRAMS on DIMM.
The data-bus width of a Rank is 64 bits (ECC is 72 bits and 8 bits ECC area is required). If the data-bus width of each bank is 4 bits, then 16 banks are required. If the data-bus width of each bank is 8 bits, then 8 banks are required. It should be noted that the Bank in the Rank does not have to be limited to the same side. There may be banks on both sides, but it is still a Rank.
Dual-Rank and Quad-Rank DIMMs can be understood as combining two or four memory modules into one memory module respectively. How many memory sticks the server can finally use, and what type of memory sticks to use depends on the number of slots on the MB and the system-level limit on the total number of ranks (total bandwidth).
Most of the products provided by Vendor, 1R and 2R are compatible, and can exist in the same Server at the same time.
In actual selection, you need to consider the number of DIMMs on the MB. If you only insert 2-4 roots, then both 1R and 2R are ok, and even 2R will increase the performance by about 5%. Once the number of DIMMs is large, it is best to choose only 1R, because the ranks cannot share the same data path at the same time. At the same time, more ranks mean more banks, which will also reduce the latency of DIMMs.
Author: cats mouse
link: https: //www.jianshu.com/p/601ceb994183
The difference between 2r 8 and 2r 4 on memory
8 is 8bit, 4 is 4bit, RANK is a memory bus (64bit), 2R 8 is 128/8, a total of 16 particles on both sides, 2R 4 is 128/4, a total of 32 particles on both sides, side is Side, generally not emphasized .