No, Mr. Dimm is not the name of a Bond villain or a not-so-smart schoolteacher in a coming-of-age comedy; MRDIMM is actually an AMD- and JEDEC-backed attempt to standardize some sort of huge, wide-bandwidth, terribly high-capacity, broadband, and somehow relatively cheap DDR5 memory in an attempt to standardize it. And now Micron (via Wccftech) has released it into the wild.

While we laypeople are accustomed to standard “non-register” RAM sticks forming the best piece of RAM for gaming, servers often use “registered” DIMMs, or RDIMMs. This buffers control instructions to improve reliability and is more important for servers than for home users; MRDIMMs (Multi-Ranked buffered DIMMs) follow this RDIMM design, but add multiple ranks of DRAM

Adding more ranks of DRAM to a DIMM allows for more memory bandwidth.

Another common way to increase bandwidth is to stack DRAMs and connect them with through-silicon-vias (TSVs), as is done with high bandwidth memory (HBM). However, this is expensive.

MRDIMMs should not be as expensive as HBM. This is because only hardware registers (buffers) need to be changed to allow multiple ranks of DRAM. Here is the trick for MRDIMM memory to operate at up to 8,800 MT/s (up to 256 GB capacity).

In a single-rank configuration, a total of two transfers, one from each rank of DRAM, which normally runs at 4,400 MT/s, are sent to the CPU at once, increasing buffer time (and thus latency) slightly but doubling the effective bandwidth. This doubled bandwidth should, in theory, more than nullify the added latency compared to a single-rank transfer rate.

This type of memory has been in development for some time now: in 2022, Intel began working with SK Hynix and Renesas to develop Multiplexer Combined Ranks DIMMs (MCR DIMMs) specifically for Intel servers. And in 2023, with AMD's support, JEDEC began developing the DDR5 MRDIMM standard.

Interestingly, Micron's MRDIMM DRAM modules are (at least for now) intended for the Intel Xeon 6 server processor. However, given that this is an open standard, one would expect AMD to introduce this into Epyc servers in the not-too-distant future.

The sight of these defective products in whichever server they end up in is intriguing, but mildly frightening. After all, they should fit; they won't work, of course, since RDIMMs are not supported on regular motherboards, but they might make for a good photo or two.

We gamers need not be discouraged by the lack of access to proprietary multi-rank DIMMs; there is plenty to look forward to in the RAM form factor department. Yes, the CAMM2, this peculiar flat one.