#1: write erase The IOS is generally stored on a piece of compact flash and copied into memory on boot. Not true for 2500 but they are old.The configuration is stored in NVRAM Non Volatile Memory so it can be retained between power off similar to c...
http://www.ebrahma.com/2013/12/10-commands-you-should-master-when-working-with-the-cisco-ios/Labels: 10-cisco-command, 10-commands, 10-commands-you-should-master, 10-commands-you-should-master-when-working-with-the-Cisco-IOS, and-router, cisco-command, Cisco-IOS, config-terminal, copy-running-configuration-startup-configuration, debug, enable, interface, master-command, no-shutdown, show-interface, show-ip-interface-brief, show-ip-route, show-running-configuration, show-version, write-erase