RAM/DRAM
During the router boot process the startup configuration, which is maintained in NVRAM, is loaded into RAM and becomes the running configuration (aka the working configuration).
Random access memory is a volatile hardware component because its information is not maintained in the event of a router reboot.
During normal operations, changes to the router’s running configuration take place in RAM.
If the administrator wants to ensure those changes are maintained, even if the system is rebooted, then he or she must copy the running configuration to the startup configuration using the command copy running-config startup-config.