nonvolatile

Nonvolatile refers to a property of computer memory and storage in which information remains stored even when power is removed. This contrasts with volatile memory, which loses its contents when supply voltage is interrupted. Nonvolatile memory is essential for long-term data retention and for storing program code, configurations, and archival data.

Common nonvolatile storage includes read-only memory (ROM), flash memory (NAND and NOR), electrically erasable programmable read-only memory (EEPROM), hard disk drives, optical discs, and magnetic tapes. In practice, many devices use combinations: firmware stored in ROM or flash, main systems in solid-state drives or hard disks, and archival data on magnetic tapes.

Advanced nonvolatile memory technologies aim to combine persistence with speed and endurance. Examples include MRAM (magnetoresistive RAM), ReRAM (resistive RAM), PCM (phase-change memory), and newer variants like 3D XPoint. Flash memory remains the dominant form for consumer storage, with wear from write/erase cycles a key design consideration; retention times can span years but vary with temperature and usage. Some nonvolatile memories offer high endurance but higher cost or lower density.

Applications include firmware storage, persistent caches, system BIOS, boot devices, mobile devices, embedded systems, enterprise storage, and archival storage. The data persistence of nonvolatile memory makes it suitable for fast recovery after power loss and for systems requiring robust long-term storage.

Future trends focus on improving speed, endurance, density, and energy efficiency, with aims to reduce reliance on slower traditional flash while offering memory-like performance and byte-addressability in persistent memory systems.