Esxi 6.7 persistent memory

hi community,

how does the persistent memory work on ESXI 6.7 and how can one set it up?

im assuming its for eg using memory in a server to install a VM onto i'm guessing? as when you create a VM and get to the customize hardware option and add new device you can add a NVDIMM and select the size in MB or GB what you want but it says i don't have any persistent memory.

Matt