|  | 4.1 | Router Componets
| 4.1.2 | Internal router's configuration components
The internal architecture of the Cisco router supports components that play an important role in the startup process, as shown in the Figure. Internal router configuration components are as follows: RAM/DRAM -- stores routing tables, ARP cache, fast-switching cache, packet buffering (shared RAM), and packet hold queues; RAM also provides temporary and/or running memory for a router's configuration file while the router is powered; RAM content is lost during a power down or restart NVRAM -- non-volatile RAM stores the router's backup/startup configuration file; NVRAM content is retained during power down or restart Flash -- erasable, reprogrammable ROM that holds the operating system image and microcode; Flash memory enables software updates without removing and replacing processor chips; Flash content is retained during power down or restart; Flash memory can store multiple versions of IOS software ROM -- contains power-on diagnostics, a bootstrap program, and operating system software; software upgrades in ROM require removing and replacing pluggable chips on the CPU interfaces -- network connections on the motherboard or on separate interface modules, through which packets enter and exit a router