Router Components

Before examining the IOS , a review of hardware and hardware terminology is useful. In addition to handling the logic of routing packets, the IOS controls the use of different physical components, which includes memory, processor, and interfaces. This section of the reviews common hardware details. All Cisco routers have a console port , and most have an auxiliary port. The console port is intended for local administrator access from an ASCII terminal or a computer using a terminal emulator. The auxiliary port, missing on a few models of Cisco routers, is intended for asynchronous dial access from an ASCII terminal or terminal emulator; the auxiliary port is often used for dial backup. Each router has different types of memory, as follows:

 RAM – Sometimes called DRAM for dynamic random access memory. RAM is used by the router just as it is used by any other computer : for working storage. The running or active configuration file is stored here.

ROM – This type of memory (read-only memory) stores a bootable IOS image. Which is not typically used for normal operation. ROM contains the code that is use to boot the router until the router knows where to get the full IOS image, or as a backup bootable image in case there are problems.

Flash memory – Either an EEPROM or a PCMCIA card. Flush memory stores fully functional IOS images and is the default location where the router gets its IOS at boot time. Flash memory also can be used to store configuration files on some Cisco routers.

NVRAM – Nonvolatile RAM stores the initial or startup configuration files.

All these types of memory, except RAM, are permanent memory. No hard disk or diskette storage exists on Cisco routers.

Cisco Router Memory Types:

RAM	FLUSH	ROM	NVRAM
Working memory and running configuration	Cisco IOS software	Basic IOS software	Startup configuration