Internal Components of a Cisco Router / Switch

Cisco Router Internal Components

--- ROM 

 
ROM is used to store the router's bootstrap startup program (which searches for a suitable system image when the router is switched on), operating system software, and power-on diagnostic tests programs. In order to perform ROM upgrades you remove and replace pluggable chips on the motherboard.

--- Flash Memory

Flash is a variation of Electrically Erasable Programmable Read-Only Memory (EEPROM). It holds operating system image(s). Flash memory is erasable, reprogrammable ROM. You can perform Cisco® IOS software upgrades without having to remove and replace chips. Flash content is retained when you switch off or restart the router.

--- RAM

RAM (Random Access Memorys ) is used to store operational information such as routing tables, router's running configuration file. RAM also provides caching and packet buffering capabilities. Its contents are lost when you switch off or restart the router. All configuration changes are saved to this file unless you explicitly save the changes to the NVRAM.

--- NVRAM

NVRAM (NonVolatile Random Access Memory) is used to store the router's startup configuration file. It does not lose data when power is switched off. So the contents of the startup configuration file are maintained even when you switch off or restart the router. The router looks for the configuration information in the NVRAM unless the router is configured to load the configuration file from some other source.

--- NETWORK INTERFACES

The network interfaces provide network connectivity to the router. The may be located on the motherboard or on separate interface modules. It may have many interfaces for LAN (Local Area Network) and WAN (Wide Area Network) connectivity. Network interfaces are diacussed in greater in next posts.