Cisco UCS servers run some of the longest-lived infrastructure in the data center: a C240 M5 bought in 2019 is often still running a production cluster today, next to M7 and M8 systems bought last year. Each of those generations takes different memory. NEMIX RAM has now completed its Cisco UCS catalog: 50 server listings covering 30 UCS servers from M5 to M8, with 1,050 module and kit configurations, plus 60 listings matched to Cisco memory part numbers. This guide explains how to tell which memory your UCS server takes, how to read a Cisco memory PID, and where to find the right module.
In this guide: Start with the generation · M8 · M7 · M6 · M5 · RDIMM or LRDIMM · Reading a Cisco PID · Population rules · FAQ
Start with the generation
The M-number at the end of every UCS model name (M5, M6, M7, M8) is the server generation, and it decides the memory. M5 and M6 servers take DDR4; M7 and M8 servers take DDR5. DDR4 and DDR5 modules are keyed differently and will not fit each other's slots. The model and generation are on the front pull-out tab and the system label, and in Cisco Intersight or UCS Manager.
| Generation | Processors | Memory | Servers in the catalog |
|---|---|---|---|
| M8 | Intel Xeon 6; AMD EPYC 9004 and 9005 | DDR5-6400 RDIMM (4800 MT/s with EPYC 9004) | C220 M8, C240 M8, C225 M8, C245 M8, X210c M8, X215c M8, X410c M8, XE130c M8, XE150c M8, C845A M8, C880A M8, C885A M8 |
| M7 | 4th and 5th Gen Intel Xeon Scalable | DDR5-4800 or DDR5-5600 RDIMM | C220 M7, C240 M7, X210c M7, X410c M7 |
| M6 | 3rd Gen Intel Xeon Scalable; AMD EPYC 7002 and 7003 | DDR4-3200 RDIMM or LRDIMM | C220 M6, C240 M6, B200 M6, X210c M6, C225 M6, C245 M6 |
| M5 | 1st and 2nd Gen Intel Xeon Scalable; AMD EPYC (C125 M5) | DDR4-2933 RDIMM or LRDIMM (2666 MT/s with 1st Gen Xeon) | C220 M5, C240 M5, B200 M5, B480 M5, C480 M5, C480 ML M5, S3260 M5, C125 M5 |
Browse by generation: DDR5 UCS servers (M7 and M8) and DDR4 UCS servers (M5 and M6), or see every UCS server listing.
M8: Xeon 6 and AMD EPYC 9005 at DDR5-6400
The M8 generation runs DDR5-6400 RDIMMs. On the Intel Xeon 6 servers (C220 M8, C240 M8, X210c M8, X410c M8) and the edge and AI systems (XE130c M8, XE150c M8, C845A M8, C880A M8, C885A M8), every listing is DDR5-6400. The AMD servers are the one place to look twice: with EPYC 9005 processors the C225 M8, C245 M8 and X215c M8 run memory at 6400 MT/s, but with EPYC 9004 processors they run it at 4800 MT/s. Each of those servers has two listings, a DDR5-6400 listing and a DDR5-4800 listing (C225 M8, C245 M8, X215c M8), so you can match the speed of the modules already installed. A DDR5-6400 module also works in an EPYC 9004 system; it simply runs at 4800 MT/s.
M7: 4th and 5th Gen Xeon Scalable
M7 servers take DDR5 RDIMMs, and the processor generation sets the speed: 4th Gen Xeon Scalable runs memory at up to 4800 MT/s, 5th Gen at up to 5600 MT/s. The C220 M7, C240 M7, X210c M7 each have a DDR5-5600 listing and a DDR5-4800 listing (C220 M7, C240 M7, X210c M7). The four-socket X410c M7 is listed at DDR5-4800, the speed Cisco lists for it with 4th Gen processors.
M6: DDR4-3200 on Intel and AMD
M6 servers take DDR4-3200: the Intel servers (C220 M6, C240 M6, B200 M6, X210c M6) run 3rd Gen Xeon Scalable, and the AMD servers (C225 M6, C245 M6) run EPYC 7002 and 7003. Every M6 server has both an RDIMM listing and an LRDIMM listing, for example the C220 M6 LRDIMM listing.
M5: the installed base
M5 is still the largest installed base of UCS memory upgrades. The Intel M5 servers (C220 M5, C240 M5, B200 M5, B480 M5, C480 M5, C480 ML M5 and the S3260 M5 node of the S3260 storage server) take DDR4-2933 with 2nd Gen Xeon Scalable processors and run it at 2666 MT/s with 1st Gen processors. With 1st Gen processors, choose the 16GB or 32GB RDIMMs or the 64GB LRDIMM; the larger modules need 2nd Gen processors. The AMD C125 M5 node is listed at DDR4-3200. As on M6, every M5 server has an RDIMM listing and an LRDIMM listing, for example the C240 M5 LRDIMM listing.
RDIMM or LRDIMM?
On M5 and M6 servers, Cisco supports both registered (RDIMM) and load-reduced (LRDIMM) modules, but never mixed in the same server. The rule is simple: match what is already installed. RDIMMs cover most configurations; LRDIMMs exist for the highest-capacity builds, such as 128GB and 256GB modules in four-socket and in-memory database servers. M7 and M8 servers use DDR5 RDIMMs only. Browse every load-reduced module in Cisco LRDIMM.
Reading a Cisco memory part number (PID)
If you are adding to modules you already have, or ordering from a Cisco quote, the Cisco PID is the fastest route. NEMIX RAM lists 60 of them in Cisco part-number memory, each matched to the capacity, rank and speed of the original module. The PID is printed on the module label and on your quote. Across the PIDs we list, the pattern reads like this:
| Part of the PID | Meaning | Examples from the catalog |
|---|---|---|
| UCS-MR… / UCS-ML… | MR is a registered module (RDIMM); ML is a load-reduced module (LRDIMM) | UCS-MRX64G2RE3 (RDIMM), UCS-ML-128G4RW2 (LRDIMM) |
| Capacity and rank | The size in GB followed by the rank count: 64G2R is 64GB dual-rank | UCS-MRX32G1RE3 is 32GB single-rank; UCS-MR128G4RE3 is 128GB quad-rank |
| DDR5 speed code | E1 = DDR5-4800 · E3 = DDR5-5600 · E5 = DDR5-6400 | UCS-MRX64G2RE1 (4800), UCS-MRX64G2RE3 (5600), UCS-MRX64G2RE5 (6400) |
| DDR4 speed code | U = DDR4-2133 · V = DDR4-2400 · T = DDR4-2933 · W = DDR4-3200 | UCS-MR-X32G2RT-H (2933), UCS-MR-X64G2RW1 (3200) |
A faster module works in place of a slower one of the same type and capacity; it runs at the speed of the server. Do not mix RDIMM and LRDIMM PIDs in one server.
Population rules for UCS servers
- Fill channels in identical groups. Install the same capacity, rank and speed across each processor's memory channels; Cisco publishes population tables for every server, and the configurations in each listing follow them (single modules, then kits sized for one processor and for the full server).
- One DIMM per channel is fastest. Adding a second DIMM per channel raises capacity but can lower memory speed on many platforms.
- Blades and compute nodes are populated per node. Each B-Series blade and X-Series compute node has its own slots; a chassis full of nodes needs a set of modules for each.
- Total capacity depends on the processor. On M5 servers, more than 1TB per processor needs an M- or L-suffix Xeon; each listing states its platform maximum.
Frequently asked questions
Which memory does my Cisco UCS server take?
Check the generation in the model name. M5 and M6 servers take DDR4 (2933 or 3200); M7 servers take DDR5-4800 or DDR5-5600 depending on the processor; M8 servers take DDR5-6400, or DDR5-4800 on AMD EPYC 9004. Search your model name to find its listing.
Can I mix NEMIX RAM with the Cisco memory already installed?
Yes, if the new modules match the installed ones in type, capacity, rank and speed. Cisco recommends identical modules within each memory channel group. When in doubt, send us the PID printed on an installed module and we will match it.
Will a DDR5-5600 module work in a 4th Gen Xeon M7 server?
Yes. It runs at 4800 MT/s, the speed 4th Gen Xeon Scalable supports. Every M7 server has both a DDR5-4800 and a DDR5-5600 listing so you can match the installed modules exactly.
Should I buy RDIMM or LRDIMM for my M5 or M6 server?
Match the type already installed, because Cisco does not support mixing them. RDIMMs cover most builds; LRDIMMs are for the largest per-module capacities.
Can I search by Cisco part number?
Yes. Type the PID, for example UCS-MRX64G2RE3, into the search bar at the top of the page, or browse the Cisco part-number collection.
Do you supply memory for a whole UCS domain?
Yes. Purchase orders, net terms and volume pricing are available for data centers, enterprises, government buyers, Cisco partners and resellers. Send us the server models and target capacity and we will quote the matching modules.
Buying Cisco UCS memory from NEMIX RAM
NEMIX RAM is a US-based server memory specialist, in business since 1993. Every module is researched, matched, and compatibility-tested by NEMIX RAM, is JEDEC-compliant, and is backed by a lifetime warranty. Purchase orders, net terms and volume pricing are available for data centers, enterprises, government buyers, Cisco partners and resellers. Request a quote for a UCS domain, a cluster refresh or a spares pool, or send us your UCS model or Cisco PID and we will confirm the right module before you order.
Start here: Cisco UCS memory guide page · all UCS servers · DDR5 (M7, M8) · DDR4 (M5, M6) · LRDIMM · Cisco part numbers