Everything about Cisco routers revolves around memory. Memory is used to boot the router, store its operating system, perform the routing process, and store the router's configuration information. To perform these tasks, four types of memory are used:
Read-only memory (ROM)
Non-volatile random access memory (NVRAM)
Dynamic random access memory (DRAM)
ROM is used on the 1600, 2500, 2600, and 3x00 series routers to handle the router's bootstrap process, and it has just enough headroom to load the OS. In the case of the 2500, the ROM set also contains a limited version of the router's operating system, called the Internetwork Operating System (IOS).
Flash memory is rewritable nonvolatile memory. In ...