RDIMM（Registered DIMM）
Dual in-line memory module with registers. The RDIMM adds a register to the memory bank for transmission. It's located between the CPU and the memory particles, which reduces the distance of parallel transmission and ensures the validity of parallel transmission.
LRDIMM（Load Reduced DIMM）
Memory buffers are used in LRDIMMs to reduce the electrical loads of the ranks to a single load. This allows up to eight ranks on a single DIMM module. Systems using LRDIMMs can be configured with the largest possible memory.
Difference module component:
| DDR3 | DDR4 |
RDIMM | Register | Register |
LRDIMM | Memory Buffer | Register + Data Buffer |
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Conclusion:
| | RDIMM | LRDIMM |
| Feature | High Speed low latency | High memory density |
| Capacity | Low | High |
| Performance | High | Low |
| Operation | Data must be transferred from each DRAM chip individually | All commands and data are communicated through the intelligent Memory Buffer. |