You may remember Allyn's article about TSV memory back from IDF 2014. Through this process, Samsung and others are able to stack dies of memory onto a single package, which can increase density and bandwidth. This is done by punching holes through the dies and connecting them down to the PCB. The first analogy that comes to mind is an elevator shaft, but I'm not sure how accurate that is.
Anyway, Samsung has been applying it to enterprise-class DDR4 memory, which leads to impressive capacities. 64GB sticks, individual sticks, were introduced in 2014. This year, that capacity doubles to 128GB. The chips are fabricated at 20nm and each contain 8Gb (1GB) per layer. Each stick contains 36 packages of four chips.
At the end of their press release, Samsung also mentioned that they intend to expand their TSV technology into “HBM and consumer products.”