For example Dell sells 4U servers straight out of their webshop which max out at 96x32GB (that's 3TB) of RAM with 4 CPUs (max 18 cores/CPU => 72 cores total). They seem to have some (training?) videos on youtube that show the internals if you are curious:

https://www.youtube.com/watch?v=vS47RVrfBvE main system board

https://www.youtube.com/watch?v=_poMPOUGRa0 memory risers