Intel has been producing Optane memory in DIMM format for servers. The DIMM format allows it to be mounted on motherboards close to the CPU. This goal is to have the memory controller have access to the Optane DIMM so that it can be used in a memory mapped fashion.
Optane is persistent ulike DRAM. This means that data stored in the Optane DIMMs will be available when a server has to reboot.
The Optane DIMM packages now reach 512GB which is far greater than the biggest server RAM sticks which top out at 128GB.
Databases are the most demanding server application I know of and they seem to like SSD storage as it has fast random access times for a SELECT command.