You’ve most likely heard of dual-channel reminiscence, however what about dual-rank? Sure, that’s one other type of reminiscence DIMM (module). In easy phrases, a dual-rank reminiscence DIMM is the equal of getting two common “single-rank” reminiscence modules on the identical DIMM. As such, a dual-rank reminiscence module ought to be twice as extensive (by way of bandwidth) as a single-rank module.
A single-rank configuration (DDR3/DDR4 module) has a width of 64-bit whereas a dual-rank module might be 128-bit extensive. Nonetheless, as a reminiscence channel is simply 64-bit extensive (identical as a single-rank module), the reminiscence controller can solely deal with one rank at a time. As you may count on, this could make dual-rank reminiscence slower than conventional single-rank modules, although they’re denser. In reality although, the distinction between the latency of single and dual-channel modules is hardly perceivable.
This is because of the truth that dual-rank reminiscence has a better variety of open rows (pages), rising the hit fee and due to this fact decreasing the prospect of a flush. On the identical time, accessing the completely different ranks induces a latency penalty, stalling the pipeline in some circumstances, thereby degrading efficiency. Due to this fact, the general influence of multi-rank modules varies from utility to utility. Usually, reminiscence bandwidth-sensitive workloads (together with gaming) profit from dual-rank reminiscence.
On shopper PCs, having all four DIMMs put in is akin to having a dual-channel, dual-rank configuration. Usually, it’s been seen that dual-rank configs are 5-10% sooner than single-rank PCs in gaming workloads, with the advantages being extra pronounced on AMD’s Ryzen CPUs.
As you may think about, there are additionally quad-rank reminiscence DIMMs as nicely that may be thought of as two dual-rank DIMMs on a single module. As soon as once more, as just one out of the 4 just one rank is accessible at a time, these modules are a good bit slower than single-rank DIMMs. For that reason, you gained’t discover quad-rank modules on mainstream PCs.
As a result of a rank is 64 or 72 bits, an ECC module produced from x4 chips will want eighteen chips for one single rank. An ECC module produced from x8 chips wants solely 9 of them for a rank. A module produced from eighteen x8 chips can be dual-ranked. An ECC module that has twice as many x8 chips might be quad-ranked. Right here, x4 and x8 signify the variety of reminiscence banks per DRAM chip.
Quad-rank DIMMs are often LRDIMMs, however in follow operate as dual-rank modules. This is because of abstraction on the a part of the LRDIMM buffer that successfully makes the quad-rank DIMM appear to be a dual-rank DIMM to the system.
This helps not solely improve the DIMM depend on servers but additionally masks the latency penalty induced by quad-rank modules (to some prolong). Most servers help as many as three LRDIMMs per reminiscence channel, considerably boosting reminiscence capability and speeds over normal quad-rank RDIMMs.
The first disadvantage with quad-rank modules is that servers at occasions are likely to restrict the variety of ranks they will deal with. For instance, a server with 4 reminiscence slots could also be restricted to a complete of eight ranks. This implies you may set up 4 single-ranked modules or 4 dual-ranked modules however solely two quad-ranked modules, as putting in extra would exceed the variety of ranks that may be addressed.
Info relating to reminiscence rank may be often discovered on the DIMM label. Single rank is often labeled as 1Rx (1Rx8/1Rx8/1Rx16), twin rank reminiscence is labeled as 2Rx (2Rx8/2Rx8/2Rx16), and quad rank as 4Rx (4Rx8/4Rx8/4Rx16). It’s essential to notice that the bodily association of DRAM chips on the DIMM doesn’t essentially point out the rank. A single-sided module might not all the time be a single-rank DIMM, and a dual-sided module might not all the time be a dual-rank DIMM and vise versa.