Non-unstable memory (NVM) or non-volatile storage is a sort of laptop memory that can retain saved information even after energy is eliminated. In contrast, risky memory wants fixed power with a view to retain data. Non-unstable memory sometimes refers to storage in memory chips, which retailer knowledge in floating-gate memory cells consisting of floating-gate MOSFETs (metal-oxide-semiconductor discipline-impact transistors), including flash memory storage akin to NAND flash and solid-state drives (SSD). Other examples of non-unstable memory embrace learn-solely memory (ROM), EPROM (erasable programmable ROM) and EEPROM (electrically erasable programmable ROM), ferroelectric RAM, most types of computer knowledge storage devices (e.g. disk storage, hard disk drives, optical discs, floppy disks, and magnetic tape), and early laptop storage strategies similar to punched tape and cards. Non-volatile memory is usually used for the task of secondary storage or long-time period persistent storage. RAM is lost. Nevertheless, most forms of non-unstable memory have limitations that make them unsuitable for use as primary storage. Typically, non-risky memory costs extra, offers decrease performance, or has a limited lifetime compared to volatile random access memory.

Typically speaking, electrically addressed methods are expensive, and have limited capability, but are quick, whereas mechanically addressed programs cost less per bit, however are slower. Electrically addressed semiconductor non-risky recollections could be categorized in accordance with their write mechanism. Mask ROMs are factory programmable solely and usually used for giant-volume merchandise which are not required to be updated after the Memory Wave brainwave tool machine is manufactured. Programmable read-solely memory (PROM) could be altered once after the memory system is manufactured using a PROM programmer. Programming is often finished earlier than the gadget is put in in its goal system, usually an embedded system. The programming is everlasting, and additional modifications require the substitute of the system. Information is saved by bodily altering (burning) storage websites in the system. An EPROM is an erasable ROM that can be changed more than once. Nevertheless, writing new knowledge to an EPROM requires a particular programmer circuit. EPROMs have a quartz window that allows them to be erased with ultraviolet light, but the whole machine is cleared at one time.

A one-time programmable (OTP) gadget may be applied utilizing an EPROM chip without the quartz window