System Startup
POST – loaded from ROM and runs diagnostics on all router hardware
Bootstrap – locates and loads the IOS image; default setting is to load the IOS from flash memory
IOS – locates and loads a valid configuration from NVRAM; file is called startup-config; only exists if you copy the running-config to NVRAM
startup-config – if found, router loads it and runs embedded configuration; if not found, router enters setup mode