LRDIMM

LRDIMM, or load-reduced DIMM, is a type of server memory module designed to reduce the electrical load that a memory controller sees on the memory bus. By integrating a buffer on the module that buffers address and command signals (and, in some designs, other control signals) before they reach the DRAM devices, LRDIMMs allow higher memory densities and greater scalability on a single channel while maintaining error-correcting, registered behavior typical of server memory.

How it works: The memory controller communicates with the on-module buffer, which in turn drives the DRAM devices. This buffering significantly reduces the capacitive load presented to the controller, enabling more DRAM chips per module and higher overall capacity per channel. Data lines are typically managed to preserve bandwidth, but the added buffering can introduce higher latency relative to unbuffered or simple registered modules. LRDIMMs come in DDR3 and DDR4 generations and are used with ECC-enabled systems.

Density and compatibility: LRDIMMs support high-capacity modules, often 16GB, 32GB, 64GB, or larger per DIMM, depending on the memory technology and motherboard capabilities. They require a platform that explicitly supports LRDIMM and is typically not interoperable with non-buffered or certain other buffered memory types. Mixing LRDIMM with RDIMM or UDIMM is generally discouraged, as it can cause instability or boot failures.

Use cases and trade-offs: LRDIMMs are favored in data centers and enterprise servers that demand large memory footprints, reliability, and error correction. The trade-offs include higher cost and potential latency increases compared to RDIMM, balanced by the ability to achieve higher per-channel capacity.