As for the matter of today's tests, our results are very clear: dual-rank memory is the way to go, as is sticking to a single DIMM per channel when possible.
The most significant performance differences in our testing are found comparing two of Samsung's 1Rx8 DDR5-4800B memory sticks in a 1DPC configuration against four of the same sticks in a 2DPC configuration. There we find that the 1DPC configuration is contently equal or better in every scenario. Using four sticks means data has to travel further along the memory traces, which combined with the overhead of communicating with two DIMMs, results in both a drop in memory performance as well as a sight increase in latency.
And while the differences between 1Rx8 and 2Rx8 are not as large, we find that there is still a difference, and it's in favor of the dual rank memory. Thanks to rank interleaving, single rank memory finds itself at a slight disadvantage versus dual rank memory, at least on today's Alder Lake systems.
Based on this data, we recommend that users looking for 64 GB of DDR5 memory opt for 2 x 32 GB, rather than using a 4 x 16 GB configuration. Besides providing the best performance, the 2 x 32 GB route also leaves room for users to add additional capacity as needed down the line. Plus, if users want to overclock them further, overclocking four sticks of memory is notoriously stressful for the processor's IMC – and DDR5 only makes this worse.
Otherwise, choosing between DDR5-4800B kits from Micron, SK Hynix, and Samsung in terms of 2 x 32 GB kits primarily comes comes down to availability and price. DRAM is a true commodity product, in every sense of the word, so for these JEDEC-standard kits, there's not much to compete on except pricing.
