Micron (Crucial) MTC40F2047S1RC56BB1R (128GB DDR5-5600 ECC RDIMM/CL46/2Rx4/3DS/1.1V/288-Pin/Registered)

3DS (3D-Stacked) DRAM uses TSV (through-silicon via) technology to stack multiple DRAM dies within one package, letting a single RDIMM hit capacities that a single monolithic die can't reach; it's the same approach used across the industry to build 128GB+ server modules. The tradeoff is longer refresh timing (tRFC1 rises to roughly 410ns here versus ~295ns on a monolithic 64GB module) and higher power draw, which is why this module carries a beefier PMIC5100-series regulator and an extra couple of PCB layers versus a standard monolithic RDIMM.

Like all server-class RDIMMs, this module combines full-chip ECC (72-bit wide, 8 check bits per 64 data bits) with a Registering Clock Driver (RCD) that buffers command/address/clock signals, plus a JEDEC SPD5118 hub IC carrying SPD data and an integrated temperature sensor (TS) for platform thermal monitoring. Its 2Rx4 rank configuration splits the 128GB across two ranks of 3DS-stacked x4 dies, so the memory controller still sees the same two-rank interleaving behavior as a 64GB 2Rx4 module, just doubled in per-rank capacity.

AMD's EPYC 9004/9005-series (Genoa/Turin) and Intel's 4th/5th Gen Xeon Scalable (Sapphire Rapids/Emerald Rapids) platforms are the most universally-supported targets for 128GB 3DS RDIMMs, with server board QVLs typically validating high-density modules at launch. AMD's Threadripper PRO 7000WX-series (WRX90) shares the same 8-channel DDR5 ECC RDIMM memory controller lineage as EPYC and can support 128GB modules, but check your specific motherboard's QVL and BIOS revision first, since early WRX90 BIOS releases sometimes lag behind on validating the highest-density 3DS RDIMMs before a firmware update adds support.

Against Samsung's M321R8GA0BB0-CQK (64GB DDR5-4800 ECC RDIMM) in this catalog, this module doubles per-slot capacity and runs a faster JEDEC bin, at a real cost premium for the 3DS stacking, worth it only when you're capacity-bound rather than budget-bound. Against SK hynix's HMCG94AGBRA177N (64GB DDR5-5600 ECC RDIMM), both run the identical 5600MT/s JEDEC speed bin and CL46 timings, so the choice is purely capacity per slot: this Micron 3DS part packs twice the density into the same DIMM socket. Against Micron's own MTC20C2085S1EC48BA1R (32GB DDR5-4800 ECC UDIMM) already in this catalog, that's an unbuffered workstation module at a quarter of this part's capacity, they serve very different roles. Against Supermicro's rebadged MEM-DR532L-SL01-ER56 (32GB DDR5-5600 ECC RDIMM, also Micron silicon), this 128GB module is the same Micron RDIMM family at four times the per-slot capacity for servers or workstations that need to maximize total RAM without adding DIMM slots.