SK hynix HMCG94AGBRA177N

Not every server board that supports DDR5 supports 5600MT/s, check your specific platform's QVL; running a 5600MT/s RDIMM on a 4800MT/s-only board just downclocks it to 4800 without causing errors, so it's a safe if not fully optimized choice either way.

This module combines full-chip ECC (72-bit wide, 8 check bits per 64 data bits) with Registered (buffered) command/address signaling: an on-DIMM Registering Clock Driver (RCD) re-times CS/CA/CLK before the DRAM dies see them, and an on-DIMM PMIC5000-series regulator generates the 1.1V DRAM rail locally from the module's 12V/5V input, both standard JEDEC DDR5 RDIMM requirements. A JEDEC SPD5118 hub IC carries SPD data plus an integrated temperature sensor (TS) for platform thermal monitoring. The 2Rx4 (dual-rank, x4) layout splits the 64GB across two ranks of 16Gb monolithic x4 dies, giving the memory controller more open pages to interleave against than a single-rank module.

AMD's EPYC 9004/9005-series (Genoa/Turin) and Intel's 5th Gen Xeon Scalable (Emerald Rapids) natively support DDR5-5600, so this module runs at its full rated speed on those platforms; 4th Gen Xeon Scalable (Sapphire Rapids) boards typically cap DDR5 server memory at 4800, downclocking this module without errors. AMD's Threadripper PRO 7000WX-series (Storm Peak, WRX90 chipset) officially tops out at DDR5-5200 ECC RDIMM, so expect this part to run at 5200 or 4800 depending on board BIOS rather than its full 5600 rating, still a fully functional, reliability-focused ECC choice for a Threadripper PRO workstation.

Against SK hynix's own smaller HMCG78MEBRA (16GB DDR5-4800 ECC RDIMM) already in this catalog, this module is both higher capacity and faster clocked, the right pick for newer platforms with headroom above the 4800MT/s baseline. Against Samsung's M321R8GA0BB0-CQK (64GB DDR5-4800 ECC RDIMM), same capacity but this SK hynix part clocks higher if your server or Threadripper PRO board supports 5600MT/s. Against Micron/Crucial's MTC40F2047S1RC56BB1R (128GB DDR5-5600 ECC RDIMM, 3DS), both run the identical 5600MT/s JEDEC bin and CL46 timings, but the Micron part doubles capacity per slot via 3DS stacking at a real cost premium, so pick this SK hynix module when 64GB per slot is enough and you'd rather not pay the 3DS density tax.