See [1]. There's not 128GB of on-chip memory. "Integrated" memory in this context means that the GPUs and CPUs all use the same memory. There are on-chip caches, of course.
It is all in integrated into one monolith “superchip” package. The 128gb of RAM isn’t going to be purchased separately or be upgradable. At least according to all indicators. Which is what I was responding to.
[1] https://www.nvidia.com/en-us/products/rtx-spark/