[codedokode]

Then what's about using 4-8 cheapest motherboards with 64Gb DDR4 and a cheap CPU, and connecting them via PCIE x16 sockets?

And as for DRAM channels, typical cheap motherboard has 2 channels and 4 slots, it should not be super difficult to add 2 more channels.

[bradfa]

To get memory mapping across systems you'd want to look into infiniband (https://en.wikipedia.org/wiki/InfiniBand) but the adapters generally aren't cheap. Common to find in super computer clusters.

If you have a desktop CPU with 2 memory channels and 2 DIMMs per channel, then the 2 DIMMs on each single channel share all of the address and data lines, there's just a chip select difference to pick which DIMM you're addressing. There is some extra loading on the lines, since you have 2 DIMMs, hence the supported speeds are usually slightly lower, but you only add 1-2 more actual PCB traces to have 2 DIMMs per channel vs 1 DIMM per channel. In contrast, adding another memory controller would add upwards of almost 100 additional PCB traces from the CPU.

[icedchai]

Don't you need a new CPU to support more channels? It doesn't sound like a cheap, trivial change to upgrade my Ryzen to a Threadripper.