As shown in the figure, a router loads the following two files into RAM when it is booted:
- IOS image file - The IOS facilitates the basic operation of the device’s hardware components. The IOS image file is stored in flash memory.
- Startup configuration file - The startup configuration file contains commands that are used to initially configure a router and create the running configuration file stored in in RAM. The startup configuration file is stored in NVRAM. All configuration changes are stored in the running configuration file and are implemented immediately by the IOS.
The running configuration is modified when the network administrator performs device configuration. When changes are made to the running-config file, it should be saved to NVRAM as the startup configuration file, in case the router is restarted or loses power.