NVRAM is nonvolatile random-access memory, which does not lose its information when the power is turned off. This is in contrast to the most common forms of RAM such as DRAM, which requires continual power to maintain its information. NVRAM is used by Cisco IOS Software as permanent storage for the startup configuration file (startup-config). All configuration changes are stored in the running-config file in RAM and, with few exceptions, are implemented immediately by the IOS. To save those changes in case the router is restarted or loses power, the running-config file must be copied to NVRAM, where it is stored as the startup-config file. NVRAM retains its contents even when the router is powered off.