The memory types and functions are the same for routers and switches
Configuring the routers is a lot of fun, but we've got to know what's going on inside the router, too! Cisco routers have four different kinds of memory, and while some of the names are similar, their purpose is totally different.
The contents of some of these memory types is kept when the router is reloaded, and others are lost on a reload. We better know which is which!
ROM: Read-Only Memory. ROM stores the router’s bootstrap startup program, operating system software, and power-on diagnostic test programs (POST).
Flash Memory: Generally referred to simply as “flash”, the IOS images are held here. Flash is erasable and reprogrammable ROM. Flash memory content is retained by the router on reload.
RAM: Random-Access Memory. Stores operational information such as routing tables and the running configuration file. RAM contents are lost when the router is powered down or reloaded. By default, routers look here first for an Internetwork Operating System (IOS) file during boot.
NVRAM: Non-volatile RAM. NVRAM holds the router’s startup configuration file. NVRAM contents are not lost when the router is powered down or reloaded.
Some important comparisons:
- RAM contents are lost on reload, where NVRAM and Flash contents are not.
- NVRAM holds the startup configuration file, where RAM holds the running configuration file.
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