Samsung has developed the world's first 128 GB DDR4 registered memory modules for servers. From the press release [businesswire.com]:
Following Samsung's introduction of the world-first 3D TSV DDR4 DRAM (64GB) in 2014, the company's new TSV registered dual inline memory module (RDIMM) marks another breakthrough that opens the door for ultra-high capacity memory at the enterprise level. Samsung's new TSV DRAM module boasts the largest capacity and the highest energy efficiency of any DRAM modules today, while operating at high speed and demonstrating excellent reliability.
From The Register [theregister.co.uk]:
The Register is aware of servers with 96 DIMM slots, which means ... WOAH! ... 12.2 terabytes of RAM in a single server if you buy Samsung's new babies.
Samsung says these new DIMMS are special because "the chip dies are ground down to a few dozen micrometers, pierced with hundreds of fine holes and vertically connected by electrodes passing through the holes, allowing for a significant boost in signal transmission."
There's also "a special design through which the master chip of each 4GB package embeds the data buffer function to optimise module performance and power consumption."