NVRAM is a separate DIMM from main memory, while NVMEM uses part of the main memory and is not a separate DIMM. The document provides examples of hardware showing NVRAM as a separate 4GB DIMM, while NVMEM on a filer uses 2.4GB of the total 20GB main memory. It clarifies the hardware difference between NVRAM using a separate DIMM and NVMEM utilizing space within main memory.