Before troubleshoot and configure Cisco devices, it is necessary to know the major components of the Cisco routers.

The given table shows all the internal components of a Cisco Router:

Components	Description
Bootstrap	It is stored in the microcode of the ROM and used to bring a router up during the initialization. It boots the Cisco router and then loads it in the IOS.
POST (Power-on-self-test)	It is used to check the basic functionality of the router hardware, and it determines which interfaces are present. It is also stored in the microcode of the ROM.
ROM monitor	It is stored in the microcode of the ROM, and used for manufacturing, testing, and troubleshooting.
Mini-IOS	It is also referred to as the boot loader by Cisco. It is a small IOS in ROM that can be used to perform maintenance operations.
RAM (Random Access Memory)	It is used to hold packet buffers, ARP cache, running configurations, and routing tables.
ROM (Read Only Memory)	It is used to start and maintain the router. It holds the POST and the bootstrap program as well as the mini-IOS.
Flash Memory	By default, it stores the Cisco IOS. Flash memory does not erase data when the router is reloaded.
NVRAM	It stands for Non-volatile RAM, which is used to hold the router and switch configuration. It does not erase data when the router or switch is reloaded.
Configuration register	It is used to control how the router boots up. This value can be found at the last line of the show version command. By default, the output is set to 0x2120, which tells the router to load the IOS from flash memory and to load the configuration from NVRAM.