Router Components
Bootstrap – stored in ROM microcode – brings router up during initialisation, boots router and loads the IOS.
POST – Power On Self Test - stored in ROM microcode – checks for basic functionality of router hardware and determines which interfaces are present
ROM Monitor – stored in ROM microcode – used for manufacturing, testing and troubleshooting
Mini-IOS – a.k.a RXBOOT/boot loader by Cisco – small IOS ROM used to bring up an interface and load a Cisco IOS into flash memory from a TFTP server; can also perform a few other maintenance operations