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Definition: non-volatile memory

Random access memory that holds its content without power being applied. There are many varieties of non-volatile memories. However, storage, which is sometimes erroneously called non-volatile memory is not one of them. Non-volatile memory refers to "byte addressable" memories that allow instructions and data to be accessed at the individual byte level (see byte addressable). See storage vs. memory, memory types and future memory chips.

Non-volatile memories are not used as a replacement for main memory in computers, tablets and smartphones. They are widely used as a cache to main memory in embedded devices, as well as a cache for solid state drives. Non-volatile memories can also be used as main memories in remote devices such as sensors, industrial controls, point-of-sale terminals as well as test and measurement equipment where only a small amount of RAM is needed. Non-volatile memories are increasingly competing in speed and cost with static RAM (SRAM), but are more expensive than dynamic RAM (DRAM) and storage (NAND flash). See cache.

Core Storage Was the First Non-Volatile Memory
Starting in the 1950s, core storage was the first byte addressable random access memory (RAM) that was widely used. Core storage lasted for about two decades, before dynamic RAM (DRAM) chips replaced it, but it is the reason memory was called "memory." The magnetic cores held their content without power (see core storage).

Following are the categories of non-volatile memory chips on the market.

The earliest non-volatile memory chips, ROMs are not updatable. PROMs and EPROMs can be updated externally and then plugged back in. These chips have been used to store boot programs and small applications. See ROM, PROM and EPROM.

NOR is a flash memory chip that is byte addressable for reading but not for writing. NOR flash differs from NAND flash, which is pure storage, whereby only large chunks of data (sectors) can be read or written. See flash memory.

MRAM is increasingly becoming a popular non-volatile memory. MRAM chips have many years of data retention and data endurance (rewritability). See MRAM.

These memories use auxiliary power (batteries or capacitors) to keep their content in case of power failure. See BBSRAM and nvSRAM.

Cypress Semiconductor's F-RAM is a non-volatile memory that uses a ferroelectric capacitor. It was the first non-volatile memory to use CMOS fabrication, the industry standard for chips. See F-RAM.

3D XPoint
3D XPoint is Intel's contribution to non-volatile memory that also serves as storage. See 3D XPoint.

One of the First Non-Volatile Memories
The first widely used RAM employed magnetic cores strung together with multiple wires, and the cores held their content without power. About 30" high, this Dataram module for a Data General minicomputer held a whopping 32KB of memory in 1967. See core storage.