SK Hynix, one of the world’s largest manufacturers of semiconductors and DRAM, has announced it has samples of a new generation of memory modules designed for HPC and servers. The technology, dubbed Multiplexer Combined Ranks (MCR) DIMMs, enables high-end server DIMMs to operate at a minimum data rate of 8 Gbps, a bandwidth increase of 80% over existing DDR5 memory products (4.8 Gbps).
Increasing memory bus (and chip) clock speeds is typically the most prevalent method for ensuring higher throughput performance on DIMMs. SK Hynix, in collaboration with Intel and Renesas, has developed the Multiplexer Combined Rank DDR5 DIMM to find a more comprehensive approach.
SK Hynix claims that their DDR5 MCR DIMMs have 66% more bandwidth than conventional DDR5 DIMMs, with an impressive 8 Gbps/pin (DDR5-8000) bandwidth. SK Hynix claims that the MCR DIMM will be ‘at least’ 80% faster than existing DDR5 memory modules, but does not specify how this figure is reached.
The technology behind the MCR DIMM is intriguing because it permits the simultaneous use of two ranks instead of one, effectively doubling the effective bandwidth by ganging up two sets/ranks of memory chips. SK Hynix claims that MCR “allows transmission of 128 bytes of data to the CPU at once,” but judging by the supplied DIMM image, there are not nearly enough pins to support a physically wider memory bus.
SK Hynix and Intel are most likely serializing the memory operations for both ranks of memory within a single DDR5 channel, allowing the two ranks to achieve an effective bandwidth of 8Gbps. This is supported by the Renesas data buffer chip, which can be seen on the DIMM in SK Hynix’s photographs. This is conceptually similar to Load Reduced DIMMs (LRDIMMs), which also employ a data buffer between the CPU and memory chips, though it is difficult to determine how similar they are.
Perhaps even more peculiar is the design’s reliance on the physical memory bus and a host controller (CPU) to support DDR5-8000 (and higher) speeds. In server-grade systems, the memory bus is typically the bottleneck in obtaining more memory bandwidth, as it must operate at slower speeds to accommodate more memory. Therefore, a strategy that requires such a fast memory bus is unorthodox. In either case, the ability to run DIMMs at DDR5-8000 speeds in a server would be a significant boost to memory bandwidth and throughput, which are frequently lacking in modern multicore chips.
Due to SK Hynix’s partnership with Intel via its MCR technology and Renesas’s buffer technology, MCR appears to be an Intel-exclusive technology, at least initially. Intel stated in SK Hynix’s press release that it “looks forward to incorporating this technology into future Intel Xeon processors and supporting industry-wide standardization and multigenerational development efforts.” In the interim, it appears that this technology is still in active development, and SK Hynix has not released any information regarding its availability, compatibility, or cost.
While SK Hynix has not elaborated on how MCR DIMM is twice as fast as conventional DDR5 memory, this product is designed for the high-performance computing (HPC) and server industries, and it is unlikely that consumer-based systems will utilize MCR DIMMs in any form. We anticipate learning more shortly.