Your motherboard probably doesn't support single 128GB DDR4 memory modules. Even if it did, and it played nice with LRDIMMs, that would be way more than you would need to run even the most demanding games. Be that as it may, Crucial has begun shipping a 128GB DDR4-2666 LDRIMM (Load Reduced DIMM) module for $4,000 a pop.
These high-density LRDIMMs are aimed at servers that run memory-dependent applications that feed off of storage density and capacity, more so than raw memory performance. They support several memory-intensive applications, including Microsoft SQL, Oracle, Microsoft Azure, VMWare VDI, Cloudera, Hortonworks, and SAP HANA.
"Performance bottlenecks weaken an organization’s infrastructure and impede overall productivity," said Michael Moreland (PDF), Crucial worldwide product manager. "Increasing the memory footprint per server can help IT managers extend the life of their current infrastructure so that workloads can thrive."
Crucial says its new RAM is optimized for Intel's latest Xeon processors, though they should work just fine with AMD's Epyc CPUs too. And if you were to fill all 16 slots on a high-end Epyc server motherboard, you would have 2TB of DDR4 RAM.
If you're looking to stick 128GB of RAM in a gaming PC, which we don't advise, there are kits out there, just no single DIMM solutions. One of the cheapest is a Corsair Vengeance LPX 128GB (8x16GB) DDR4-2133 memory kit for $1,450. That almost seems like a bargain.