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Non-volatile memory, nonvolatile memory, NVM or non-volatile storage is computer memory that can retrieve stored information even after having been power cycled (turned off and back on). Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM (F-RAM), most types of magnetic computer storage devices (e.g. hard disk drives, floppy disks, and magnetic tape), optical discs, and early computer storage methods such as paper tape and punched cards. Non-volatile memory is typically used for the task of secondary storage, or long-term persistent storage.〔"(A Survey of Software Techniques for Using Non-Volatile Memories for Storage and Main Memory Systems )", IEEE Transactions on Parallel and Distributed Systems, 2015.〕 The most widely used form of primary storage today is a volatile form of random access memory (RAM), meaning that when the computer is shut down, anything contained in RAM is lost. However, most forms of non-volatile memory have limitations that make them unsuitable for use as primary storage. Typically, non-volatile memory costs more, provides lower performance, or has worse write endurance than volatile random access memory. Several companies are working on developing non-volatile memory systems comparable in speed and capacity to volatile RAM. IBM is currently developing MRAM (Magnetoresistive RAM). Not only would such technology save energy, but it would allow for computers that could be turned on and off almost instantly, bypassing the slow start-up and shutdown sequence. In addition, Ramtron International has developed, produced, and licensed ferroelectric RAM (F-RAM), a technology that offers distinct properties from other nonvolatile memory options, including extremely high endurance (exceeding 1016 read/write cycles for 3.3 V devices), ultra low power consumption (since F-RAM does not require a charge pump like other non-volatile memories), single-cycle write speeds, and gamma radiation tolerance. Other companies that have licensed and produced F-RAM technology include Texas Instruments, Rohm, and Fujitsu. Non-volatile data storage can be categorized in electrically addressed systems (read-only memory) and mechanically addressed systems (hard disks, optical disc, magnetic tape, holographic memory, and such). Electrically addressed systems are expensive, but fast, whereas mechanically addressed systems have a low price per bit, but are slow. Non-volatile memory may one day eliminate the need for comparatively slow forms of secondary storage systems, which include hard disks. == Electrically addressed == (詳細はMask ROMs are factory programmable only, and typically used for large-volume products not required to be updated after manufacture. Programmable read-only memory can be altered after manufacture, but require a special programmer and usually cannot be programmed while in the target system. The programming is permanent and further changes require replacement of the device. Data is stored by physically altering (burning) storage sites in the device. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Non-volatile memory」の詳細全文を読む スポンサード リンク
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