What Is LRDIMM Memory? LRDIMM vs RDIMM vs UDIMM
LRDIMM (load-reduced DIMM) is a server memory module that buffers more of the electrical signal load than an RDIMM does. This lets a server use larger modules and more modules per channel, so it can reach much higher total memory capacity. It costs more, draws more power and adds a little latency compared with RDIMM and UDIMM.
LRDIMM vs RDIMM vs UDIMM Compared
| UDIMM | RDIMM | LRDIMM | |
|---|---|---|---|
| Electrical load on the controller | Full load | Reduced command and address load | Minimal load |
| Latency | Lowest | Middle | Highest |
| Typical maximum capacity | Under 256GB per system | 1 to 4TB per server | 4 to 8TB or more, depending on CPU platform |
| Multiple modules per channel | Often slows down at 2 per channel | Supports 2 per channel at higher speeds | Best for 2 or 3 per channel with high-rank modules |
| Power draw | Lowest | Middle | Highest |
| Typical use | Desktops, workstations, entry-level servers | Most production servers | Maximum-density servers |
LRDIMM vs RDIMM
An RDIMM places a register chip on the command, address and clock lines. An LRDIMM goes further and buffers more of the signal path, which cuts the load each module places on the memory bus. The result is more capacity per channel. In an older HPE ProLiant Gen9 comparison, LRDIMMs allowed roughly four times the memory of RDIMMs. The trade-offs are higher cost, slightly higher latency and more heat, so LRDIMM servers need good airflow.
Which One Should You Choose?
- RDIMM: the default for most servers. It balances capacity, speed and price.
- LRDIMM: choose it when capacity per socket matters most, such as large virtualization hosts, in-memory databases and AI nodes with terabytes of RAM.
- UDIMM: choose it for desktops, small servers and NAS systems where cost and low latency matter more than capacity.
Check platform support first. LRDIMM needs a CPU and motherboard that list it, and you must not mix LRDIMM, RDIMM and UDIMM in one system.
Frequently Asked Questions
What does LRDIMM stand for?
Load-reduced dual in-line memory module.
Is LRDIMM faster than RDIMM?
Not at the module level. LRDIMM has slightly higher latency. Its advantage is capacity and the ability to keep speed up when many modules are installed.
Can I mix LRDIMM and RDIMM?
No. Use one type across the system.