Routers CPU, OS and Memory

In chapter 1 we have already studied the general introduction of the router here we will briefly discuss routers. It is similar to a computer. Regardless of their function, size or complexity, all router models are basically computers. Just like computers, tablets, and smart devices, It also requires:

• Central processing units (CPU)


• Operating systems (OS)


• Memory consisting of random-access memory (RAM), read-only memory (ROM), nonvolatile random-access memory (NVRAM), and flash.

Here in this section, we will discuss Cisco routers. Like all computers, tablets, gaming consoles, and smart devices, Cisco devices require a CPU to execute OS instructions, such as system initialization, routing functions, and switching functions.

Central Processing Unit (CPU)

The central processing unit (CPU) of a router is a hardware that carries out the instructions of the OS to perform routing and switching.  The CPU is sometimes also referred to as the central processor unit or processor for short. The CPU generates interrupts (IRQ) in order to communicate with the other electronic components in the router.

Routers Operating System

The Cisco Internetwork Operating System (IOS) is the operating system used for most Cisco devices. Cisco IOS is a family of software used on most Cisco routers, Cisco network switches, Cisco access points and many other devices. Earlier switches run CatOS.  IOS is a package of routing, switching, internetworking and telecommunications functions integrated into a multitasking operating system. Routers Memory-Cisco router uses four types of memory which are following:

Random Access Memory(RAM)

RAM is a hardware device that allows information to be stored and retrieved on a router. This is volatile memory used in Cisco routers. This memory store application, processes, and data needed to be executed by the CPU. Cisco routers use a fast type of RAM called synchronous dynamic random access memory (SDRAM).  As we know that it is a volatile memory and requires power to keep the data accessible. If the router is turned off, all data contained in RAM is lost.RAM has following the main function:

• Store routing table.


• Running IOS.


• Store ARP Table


• Packet buffer


• Store running configuration file.

ROM

The ROM is used to start and maintain the router. This is a volatile memory of the router. It contains some code, like the Bootstrap and POST, which helps the router do some basic tests and boot up when it's powered on or reloaded. ROM is firmware embedded on an integrated circuit inside the router which can only be altered by Cisco You cannot alter any of the code in this memory as it has been set from the factory and is Read Only. ROM stores the following:

• Bootup information that provides the startup information.


• Power-on self-test (POST)


• Limited IOS to provide a backup version of the IOS. When full feature IOS has been deleted or corrupted, this limited IOS is used to restore full featured IOS.

NVRAM

This is non-volatile RAM. The NVRAM is a place where the router holds its configuration. This is the permanent memory storage of the router. When you configure a router and then save the configuration, it is stored in the NVRAM. This memory is not big at all when compared to the system's RAM. When a router starts up after it loads the IOS image it will look into the NVRAM and load the configuration file in order to configure the router. The NVRAM is not erased when the router is reloaded or even switched off.

Flash

Flash memory is non-volatile memory used as permanent storage for the IOS and other systems related files such as log files, voice configuration files, HTML files, backup configurations, and much more. When a router is rebooted, the IOS is copied from flash into RAM. The RAM is an EEPROM (Electrical Erasable Programmable Read Only Memory) card. It fits into a special slot normally located at the back of the router and contains nothing more than the IOS image. Usually, it comes in sizes of 4MB for the smaller routers and goes up from there depending on the router model.