|  | 4.1 | Router Components
| 4.1.3 |
RAM for working storage in the router
RAM is the working storage area for a router. When you turn a router on, the ROM executes a bootstrap program. This program performs some tests, and then loads the Cisco IOS software into memory. The command executive, or EXEC, is one part of the Cisco IOS software. EXEC receives and executes commands you enter for the router. As shown in the Figure, a router also uses RAM to store an active configuration file and tables of network maps and routing address lists. You can display the configuration file on a remote or console terminal. A saved version of this file is stored in NVRAM. It is accessed and loaded into main memory each time a router initializes. The configuration file contains global, process, and interface information that directly affects the operation of a router and its interface ports. An operating system image cannot be displayed on a terminal screen. An image is usually executed from the main RAM and loaded from one of several input sources. The operating software is organized into routines that handle the tasks associated with different protocols, such as data movement, table and buffer management, routing updates, and user command execution.