Non-volatile refers to a type of computer memory or storage that can retain stored information even after power is removed. In contrast, volatile memory needs constant power to retain data. Examples of non-volatile memory include flash memory, read-only memory (ROM), ferroelectric RAM, most types of magnetic computer storage devices (e.g. hard disk drives, floppy disks, and magnetic tape), and optical discs. Non-volatile storage is often used for secondary storage or long-term persistent storage. 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. Non-volatile memory typically costs more, provides lower performance, or has a limited lifetime compared to volatile random access memory.