CPU and memory of vro components!

Despite the diversity of vro types and models, each vro has the same common hardware components. The positions of these components in the vro vary depending on the model.

Router components and functions

Like a PC, a vro also includes:

CPU)

Random Access Memory (RAM)

Read-only memory (ROM)

Logic Diagram of the internal components of the Cisco 1841 vro

CPU

The CPU executes operating system commands, such as system initialization, routing, and switching.

RAM

RAM stores the commands and data that the CPU needs to execute. RAM is used to store the following components:

Operating System: at startup, the Operating System copies Cisco IOS (Internetwork Operating System) to RAM.

Run the configuration file: This is the configuration file that stores the configuration commands currently used by the router IOS. Except for a few special commands, all the commands configured on the vro are stored in the running configuration file, also known as running-config.

IP route table: This file stores information about the directly connected network and remote network, used to determine the optimal route for packet forwarding.

ARP cache: This cache contains the ing between IPv4 addresses and MAC addresses, similar to ARP cache on a PC. ARP cache is used on a router with a LAN interface (such as an Ethernet interface.

Data Packet Buffer: After the data packet arrives at the interface and before it is sent from the interface, it will be temporarily stored in the buffer.

RAM is a volatile memory. If a vro is powered off or restarted, its content will be lost. However, routers also have permanent storage areas, such as ROM, Flash, and NVRAM.

ROM

ROM is a permanent storage. Cisco devices use ROM for storage:

Bootstrap command

Basic diagnostic Software

Lite version IOS

ROM uses firmware, that is, software embedded in the integrated circuit. Firmware contains software that generally does not need to be modified or upgraded, such as startup commands. Many similar features (including ROM monitoring software) will be discussed in subsequent courses. If the router is powered off or restarted, the content in the ROM will not be lost.

Flash Memory

Flash memory is non-volatile computer memory and can be stored and erased electronically. Flash memory is used as a permanent storage for the operating system Cisco IOS. In most Cisco router models, IOS is permanently stored in flash memory and copied to RAM during startup before being executed by the CPU. Some earlier Cisco router models run IOS. Flash Memory directly from the flash memory and are played by the SIMM card or PCMCIA card. You can upgrade these cards to increase the flash memory capacity.

If the router is powered off or restarted, the content in flash memory will not be lost.

NVRAM

NVRAM (non-volatile RAM) does not lose information after the power is off. Unlike most common RAM (such as DRAM), the latter requires continuous power to maintain information. NVRAM is used by Cisco IOS as a permanent storage for the startup configuration file (startup-config. All configuration changes are stored in the RAM running-config file (except for a few special cases) and are executed by IOS immediately. To save the changes to prevent the vro from restarting or powering off, you must copy running-config to NVRAM and store them as the startup-config file. NVRAM does not lose its content even if the router is restarted or powered off.

For network engineers, it is more important to understand the functions of the main internal components of a router than the specific positions of the internal components of the router. The internal physical architecture of a vro varies depending on the model.