Non-Volatile Memory 

Non-volatile memory is a type of memory that retains its data when power is removed from the circuit.  Whereas volatile memory loses its data when power is turned off.  Computers, CD-ROM's, cellular phones, compact flash cards, digital cameras, MP3 audio recorders, and smartcards all use non-volatile memory. 

MRAM, Flash, EEPROM, EPROM, FeRAM/FRAM, NVSRAM and ROM are different types of non-volatile memory.  The main differences are in the memories relative cost per bit and the flexibility to accommodate code changes.

	PRAM / OUM (Phase Change Memory)        Wiki
	Ovonic Unified Memory also called Phase Change Mamory is a technology developed by Ovonyx Inc. The process uses chalcogenide phase change material to implement non-volatile memory storage. Chalcogenide material is a viable candidate for next generation NVM. The basic phase change material is a GeSbTe alloy and is in the same family of material used in optical re-writable CD/DVD RW  but implemented at the chip level.
	MRAM                      Wiki
	Magnetoresistive RAM incorporates spintronics (spin-based electronics) technology to control the resistance of  thin-film magnetic multilayered structure. MRAM is proposed as the next generation of memory, combining the best features of current memory technologies-including the high density of DRAM, the high speed of SRAM and the non-volatility of flash.
	EPROM                    Wiki
	Erasable Programmable Read Only Memory also known as UV-EPROM (Ultra Violet Erasable Programmable Read Only Memory) is a form of non-volatile memory.  It is programmed electrically at high voltage using a charge that is injected into the floating gate.  Data is erased by exposing the EPROM to UV light.  The memory chip may then be re-programmed with new data.  Since the memory element is a single floating gate transistor the devices are manufactured in relatively high density.  EPROMs are expensive because of the special quartz window packaging required for erasing capability.  EPROMs are quickly being replaced by FLASH memory devices.
	EEPROM                   Wiki
	Electrically Erasable Programmable Read Only Memory is a type of non-volatile memory that uses a floating gate technology.  EEPROMs allow data to be reprogrammed on a byte by byte basis.  Unlike EPROMs that use UV light, these devices can be erased electrically so there is no need for a window in the package.  EEPROMs are used for storing data that is not changed often.   Compared to DRAM, EEPROMs have a much slower read and write cycle.  EEPROMs are also more expensive and less dense than RAM.
	FLASH                       Wiki
	In this device data is erased and reprogrammed in blocks, unlike the byte by byte altering capability of EEPROM.  FLASH memory has the density of EPROMs and the electrical erase capability of standard EEPROMs.  FLASH is used in digital cameras to store pictures, PC's store their BIOS on FLASH memory chips, and MP3 audio recorders use FLASH to store music.
	NVSRAM                   Wiki
	There are two types of Non-Volatile Random Access Memory.  One uses a battery built in to the device to maintain the data when main power is turned off.  The second type has both RAM cells and EEPROM cells.   This second type saves the RAM data into the EEProm cells before power is removed and then reloads the RAM when power is restored.  This type of memory has the read/write speed of static RAM combined with the non-volatility of EEPROM.  Low density and high cost are the major drawbacks to NVSRAM.
	FeRAM / FRAM         Wiki
	Ferroelectric Random Access Memory is a type of non-volatile memory that consists of a ferroelectric capacitor and MOS transistor.   FeRAM changes state when exposed to an electric field.  FeRAM read and write speeds are similar to SRAM with the non-volatility and in-circuit programmability of EEPROM.  It is replacing EEPROM in many devices because of its speed.  The biggest drawbacks to FeRAM devices were high cost and low density.  However, this is rapidly changing due to a significant amount of research and development being invested in ferroelectric material.
	PROM                          Wiki
	Programmable Read-Only Memories are memory devices that can only be programmed once, but never changed.  Data written to PROM's is permanent.  The device is manufactured in a "blank" state and programmed by the user.   Unlike ROM, which is programmed by the manufacturer.  Data is written to a PROM using a PROM programmer.
	ROM                              Wiki
	Read-Only Memory is a type of non-volatile memory, it retains data when power is turned off.  Data stored in ROM is permanent and can not be modified once the device is fabricated.  ROM is used to hold programs in embedded systems, to store firmware in computers, and video game cartridges utilize ROM to store programs.