One DIMM, Two Independent Channels
DDR5 splits the traditional 64-bit channel (72-bit with ECC) into two 32-bit sub-channels, each carrying 8 bits of ECC and each with its own command/address bus. From the memory controller's view a single DIMM now services two independent transaction streams concurrently; with burst length moving from BL8 to BL16, the data moved per access stays the same while parallelism doubles. The gain is clearest on random-access-heavy server workloads, and it is the structural reason DDR5 outperforms DDR4 even at equal data rate.
Power Management Moves onto the Module
DDR5 relocates the PMIC from the motherboard to the DIMM, with the module generating its internal rails from 12 V. Regulating closer to the load improves droop and noise control and simplifies the board-level power distribution network. The cost is higher module bill-of-materials complexity, greater component height and additional self-heating, so PMIC and SPD Hub placement must stay clear of the DRAM thermal path — a constraint that dominates low-profile designs such as VLP ECC RDIMM.
On-Die ECC Is Not System ECC
DDR5 dies include on-die ECC to correct the single-bit array errors that process scaling makes more frequent. It is invisible to the memory controller and never reported to the operating system: it is a yield-enabling mechanism, not a reliability feature offered to the system. Servers still depend on system-level ECC across the RDIMM to cover bus and device errors and to report them. Conflating the two leads to a serious overestimate of what a non-ECC module provides.
Higher Rates, Tighter Signal Integrity Margins
The RCD on an RDIMM buffers and re-drives command/address signals, reducing the load presented to the controller. Going from 4800 to 6400 MT/s shrinks the unit interval further, tightening tolerances on trace length matching, reference plane continuity, via stub length and connector loss, and shifting more compensation burden onto training routines such as write levelling, read eye centring and DFE coefficient search. Capacity growth relies on 3DS stacking, reaching specifications such as 3DS ECC RDIMM at 256GB within a fixed module area.
Portfolio Coverage
The DDR5 server memory line covers RDIMM at 4800 and 6400, ECC UDIMM at 5600, VLP ECC RDIMM and 3DS ECC RDIMM 256GB. Alongside DDR4 RDIMM, ECC UDIMM and LRDIMM, and E3.S-based CXL 2.0 memory expansion, it addresses memory configuration needs across platform generations.