When the copy running-config startup-config command is issued on a router, the configuration is saved in the non-volatile random access memory (NVRAM) memory. The copy startup-config running-config command copies the version in RAM to NVRAM.

Note: For the copy startup-config running-config command to function, there must be a configuration already residing in RAM. For example, a brand-new router with no configuration created would have no startup configuration in RAM. If you attempted to execute the copy startup-config running-config command in that case, you would receive the following error message

%% non-volatile memory configuration is invalid or not present

In addition to storing the running configuration in the NVRAM, you can also store it on a Trivial File Transfer Protocol (TFTP) server. When a router boots in the absence of a startup configuration, the router will look for a valid configuration on a TFTP server. In the case that the TFTP server also does not have a valid router configuration or is unreachable, the router will enter the setup dialog and prompt the user to provide initial configuration inputs.

The router does not store the startup configuration in random access memory (RAM). RAM only holds the running configuration that is loaded from the NVRAM or TFTP server during the boot process.

The router does not store the configuration in flash or read-only memory (ROM). ROM contains the bootstrap code, while flash memory contains the IOS image