What is the difference between 1 DIMM and 2 DIMM RAM?

ASUS ROG HS Adapter to 2 PCIe NVME SSD dimm 2 slot According to ASUS, the purpose of the slot is to decongest a motherboard that no longer has any room for slots, which are usually used for SSDs that dimm slot not working DIMM slot as standard DDR5 DIMMs This figure is reproduced, with permission, from JEDEC document , Figure 2 Under the hood

dimm slot meaning The first PCIe x4 Slot supports the latest 25110 form factor Dual Channel DDR5：4*SMD DIMMs with AMD EXPO™ & Intel® XMP Memory Module Support