NVRAM, DRAM, SRAM

Non-Volatile random access memory.
E.g. flash disk
it will not loose data after power off
Dynamic random access memory (DRAM) and Static random access memory (SRAM) will need power to keep data.
DRAM: volatile, need periodically refreshed (home PCs are DRAM)
SRAM: volatile

NVRAM fast than disk, but it more expensive