There are three major parts of the router that can be upgraded:DRAM memory, Flash Memory, and the IOS operating system that runs on it.DRAM and Flash can each be a maximum of 16 MB (try ebaying for cisco 2500 flash or memory), and IOS images can be downloaded from Cisco if you have a valid Cisco service contract.
flash, NVRAM, TFTP server
Flash Memory
TFTP server, Flash
The Security device manager is stored in the Router's Flash Memory
config tftp run
Flash MemoryTFTP server
the following information will be displayed when show version command is issued in a cisco router :IOS versionSystem uptimeImage filenameType of processorAmount of RAMNumber of portsAmount of flash memoryCurrent configuration register
flash
Cisco routers contain 4 types of memory:DRAM, which is used in the same way as RAM in your PC to contain running programs, as well as buffer the data being routed etc.NVRAM, which stores the startup-config configuration used by the router to determine what it should be doing.Flash, which contains a copy of the IOS operating system and acts as the router's 'hard drive'ROM, used to permanently house the bootup sequence and a minimal version of IOS that's mostly intended to let you load a real IOS into flash.
to TFTP
In flash memory. This is the equivalent of what, in a PC, would be the hard disk. However, when the router or switch is turned on, a copy of the IOS file is loaded into RAM. This, too, is equivalent to a PC, which needs to load its programs into RAM.