A non-volatile memory(NVM) is a programmable circuit that permanently stores its data once it has been entered, without the need for additional power. The data can be erased and stored again. Nonvolatile memory can be semiconductor-based, ferrite-based, metal oxide-based, bubble memory, or amorphous.
Non-volatile memories differ in their storage capacity, storage method, access times and integration density. Non-volatile memories are used in almost all electronic devices: In processor systems, personalcomputers, embedded systems, industrial equipment, smartphones, in automotive technology, in consumer electronics devices and home automation. In these devices and systems, they permanently store program code, data tables and other data and make them available for program execution.
Semiconductor memories as non-volatile memories
Semiconductor memories use the stable states of flip-flops for permanent storage, as with all read only memories( ROM) and phase change RAMs( PRAM). Flash memories rely on special MOSFETs that retain charge and are interconnected as NAND gates, the NAND flashes. The NVMe(NVMe) protocol was developed for them, which is designed for flash mass storage with many internal channels and multi-core processors.
Programmable devices include Read Only Memories (ROM), Programmable Read Only Memories( PROM), Erasable PROMs( EPROM), Electrically Erasable PROMs( EEPROM), Flash memory, Generic Array Logics ( GAL), Programmable Array Logics( PAL), Complex Programmable Logic Devices ( CPLD) and several more. These programmable devices are programmed using programming devices.
Magnetic memories as non-volatile memories
Magnetic materials exploit remanence and bubble memories exploit the presence or absence of a magnetic field. With semiconductor-based flash technologies, storage capacities of around 50 Gbit are achieved thanks to the high integration density with structure widths of 40 nm. A non-volatile memory that uses amorphization is phase change memory( PCM). Resistive RAM( RRAM), in which the conductivity of the material is changed, forms another principle of a non-volatile memory.
In addition to non-volatile memories, there are volatile memories. They store their input data only as long as they are supplied with a supply voltage.