In Router Memory, there are different types of memories in it. It stores the information in the various memory components of router memory.

They are :

  1. ROM
  2. NVRAM
  3. FLASH
  4. RAM


The ROM is a read-only memory. The ROM brings a lot of important content. We can store the Routers Bootstrap startup program The bootstrap program is the starting program that we execute in a system. If we do not have any other memory components on the router the bootstrap is the startup program in the device. The power of the hardware of the Equipment is a startup at the ROM memory. It determines the capacity of the hardware devices in the system. so the bootstrap memory is the startup program in the systems.

Random access memory ROM

This ROM is the permanent storage memory and does not lose the content when the system is turned off. Mostly the ROM is used to maintain the Router. It stores all bootstrap programs to test the programs. It contains the bootstrap program called the ROM monitor. The Routers powered on the bootstrap runs the hardware power diagnostic test programs or the POST. If the POST runs successfully, these bootstrap attempts to load the Cisco IOS in the flash memory.

The Flash memory can be overwritten or erased if the bootstrap doesn’t find the IOS in the version of the IOS. If the Router cannot hold the full-featured IOS. The routers cannot load the full-featured IOS if the router only provides the full-featured version of IOS.

We cannot make any changes in the ROM, if we want to replace, or overwrite the existing content, The Entire ROM chip needs to be replaced if any upgrade or replacement is necessary.

Types Of the Cisco Routers

These Routers can have both internal and External components operations. Let us discuss the different Router components and their functions in the Router.

The Internal Components of the Router CPU. memory components, power supply, and the config registers. The External components are Management ports. Lan and Wan interface, USB ports, Flashcard slots, and EHWic slots. Let us know the introduction to each of the External components of the Routers.

  1. CPU: We all know CPU as the computer processing unit that processes and displays the data in the monitor. The CPU does all the Operations in the Operating system instructions. It Executes all the algorithms like Shortest path, Dijkstra’s algorithm, and many more operations are done by the CPU.
  2. RAM: It stands for Random access memory, It is volatile in nature. It loses its power when the system is shut down or off immediately if any system crashes. The Infomation in the random access memory can be stored temporarily. All the Information or data and instructions are executed by the CPU.

There are many more features in Random access memory(RAM). It stores the Operating systems, IOS is copied by the RAM during the bootstrap program execution. All the running configuration files, IP routing tables files, Packet Buffers, ARP caches are executed in the RAM itself.

The Next component we are discussing the NVRAM :

The NVRAM stands for the Nonvolatile random access memory.

It transfers all the Nonvolatile data or information. The definition defines the data or information will not be lost even the system breaks the connection or shutdowns suddenly.

The below-given figure represents the NVRAM inside the Router. The mentioned number 5 is NVRAM.

This NVRAM can store all the startup files, configuration files, backup files, and all. The startup files are bootstrap programs that we execute at the starting of the system. This NVRAM is used to store the permanent storages in the Cisco IOS Operating systems.

When the Router wants to reboot the system, it checks for the configuration of the files in the NVRAM, only if the router wants to configure information from the Router source.

When the NVRAM is empty, it reloads the data and prompts the data into the setup mode.

The NVRAM is very cost expensive to build the nonvolatile ram. There are many more NDM projects. Resistive RAM, RAM nano, RAM spin that drives the world in the future. The NV RAMs make all the commercial and the financial sense.

Flash Memory

This Flash memory is a permanent storage memory. It is also similar to the NVRAM and the RAM as nonvolatile in nature. These flash memories can also store all the other system-related files in it.

The Flash memory is the type of EEPROM that can electrically be stored and erased to make the CISO IOS upgradable. The most model of cisco routers, the ios is stored permanently and stores in the flash memory. and these IOS is copied into the ram during the bootstrap process. The bootstrap process is then executed by the CPU(Central Processing Unit).

Power Supply

The Power supply is a component that supplies power to the router and its component. These power supplies can either be AC or DC. There are 19400 power supplies are visible in the diagram shown below. Most of the Routers consists of multiple power supplies for the Redundancy in the data.

Configuration register

The interesting topic is the configuration register. It tracks where the router is going to boot the IOS image. The default value of the configuration register is 0X – 10. It Tells the Router to load the IOS from the flash memory and to load the configuration from the NVRAM.

The configuration register can be found in the command version of the NVRAM

The next topic in the types of routers are the External components :

These External components are present at the backside of the routers. There are many different types of ports, interfaces, and router models are present. The Router interfaces are different according to the type and need of the routers.

let us discuss the different types of ports :

Management ports

These Management ports again consist of two types:

  1. Console ports
  2. Auxiliary ports

These two ports are used to troubleshoot and configure the router.

Console ports

These Console ports are used to access the initial configuration and also access the admin configuration and the command-line interface. There are two types of ports we used :

  1. RJ45
  2. B USB connector

The console can access only one port at a time. It connects directly to the switch or a router.

Auxiliary ports

An RJ45 port is used for the remote and administration access, similar to the console ports. The Auxiliary ports are considered as the old ports.

The auxiliary ports are used in the dial-up modems.

LAN interfaces

Another topic in the components is called the LAN interfaces. It includes the 2*10/100/1000. The interfaces with GE 0/0 and 0/1. These interfaces are generally used to provide LAN access by connected switches to interconnect to the other devices.

USB interfaces

These USB interfaces are included for the additional storage space. USB 0 and USB 1 are the additional storage space that similar to the flash memory. Then we have the H Weak slots that provide modularity and flexibility by enabling the router. To support the different types of interfaces, serial module, digital subscriber, switch port, and wireless ports. This supports the extended capability.

Working and Functions of the Cisco Router

Let us know the detailed function of the Cisco Router. Suppose if we want to transfer the messages from one Network to another Network. A connection must establish between the two user computer by using a cross over cable. The Cross over cable is nothing but the Ethernet cable. We can connect the two devices. These two devices have a proper network at the data link layer and a strong wire at the physical layer.

Now at the network address, we assign the IP addresses to each device. Let us take an example, the below diagram represents the basic data transfer between the devices.

working of Cisco router

To send a message from the sender to the receiver. We define an IP address at each side of the network device. Suppose network one has the IP address of and network 2 has the IP address of with the network address of at both ends of the computers. With the address of we can conclude it as the network address. With the same network address at both ends, we can easily travel the data at both ends of the network.

In contrast, if we change the IP address of one of the user computers, we cannot send the messages to that changed address router due to the change in the user’s network IP address.

To fix the above problem, and allowing users to communicate in different network addresses, The Router introduced.

The components in routers are similar to those in computers. The Router consists of a processor, storage space, flash drive, hard drive, and also consists of the network card interfaces. Every router consists least of two network card interfaces.

Use of Network Interfaces

Now, these Network interfaces are used at both ends of the user networks. If the Network card interface and the IP address of another network match then we can send the messages or data between the two devices in the back and forth way. It sends the packets from one router to the other Router. Suppose if a Home network, the Network portion of the router and our Home network are alike. The Network portion on the inside of the network is different from the network portion outside of the network.

The functioning of the memories in the Cisco Router :

The Cisco routers consist of several different memories. Each memory performs different operations in the Cisco Router. POST, ROM, RAM, FLASH, NVRAM are the memories in the cisco router. The first most component in the cisco router is ROM. This ROM loads the bootstrap program into the memory and searches for the IOS operating systems. The Bootstrap program is the first program that executes in the computer system. It guides how the operating system IOS should be loaded and how the program, is to be executed.

Another component is the POST, this post self checks the data in the devices and test all the hardware devices.

Another best component is the FLASH component, this flash stores the IOS operating system in it. These IOS is loaded during the execution of the bootstrap program. NVRAM is another component of the RAM. It stores the configurations permanently and the startup configuration is executed.

The RAM stands for the random access memory. It stores all the temporary configurations in the memory. The data or information cannot be stored permanently, it deletes the data after the system is turned off.

All these belong to the internal components of the Cisco routers.

Now let us talk about the external components and their working in the cisco routers. LAN, WAN, and the admin ports of the router. All the internal ports are categorized into three types, LAN, WAN, and admin ports. The LAN connects the connects to a switch, which all the connections to the router. All these LANs connect to a remote location, which we call it has the Wide area network.

LAN(Local Area Network) ports

It is a local area network. Ethernet, fast ethernet, gig Ethernet are the three different rates in Ethernet. The simple Ethernet is at a data rate of 10Mbps, the fast Ethernet is at the data rate of 100 Mbps, and the gig is at the highest data rate of 1000 Mbps. These LAN ports are look similar to the RJ45 connectors. The Fast Ethernet acts as the default ethernet for most of the LAN ports. But mostly, of the 1000Mbps and the 100 Mbps are used for Local Area Ports.

WAN(Wide Area Network) ports

The WAN ports are connected at remote locations. In the Ethernet, we call the WAN ports the serial ports. There are two types of serial ports. One is the 26 pin serial ports and another one is the 60 pins serial port. 60 pin is the older pin. nowadays, 20 pin serial ports are used. These 26 pin ports are mostly called the smart pins. We can find one serial port, two serial ports in the wide-area network.


The Admin ports don’t share the data between the two networks but actually, transmits the commands from the two devices.

Summary of Router Memory

There are different types of memories in the router. The ROM is the Read-only memory. In these ROM we can store the Bootstrap program.

If we don’t have the other programs in the router we first execute the bootstrap program. The capacity of the hardware devices is determined by the Read-only memory. Hence we consider the bootstrap program as the startup program in every system.

The ROM is a permeant storage memory. when the system is turned off or disconnected there will be no loss of data in it. The IOS is loaded into the operating during the execution of the bootstrap program. If any data or content wants to be replaced or overwrite we have to change the entire ROM chip.

There are different types of cisco routers in it. It consists of both internal routers and external routers in it. CPU, RAM, NVRAM, and all come under the internal components of the router. A Cisco Router consists of all the components that are present on the computer.

The NVRAM can store all the startup files and stores the permanent operating systems. These flash memory can also store all the system-related files in it.

This Flash memory is the type of EEPROM that electrically stores to make CISO IOS Upgradable. Console ports, LAN interfaces, WAN interfaces, USB interfaces, Management ports, configuration ports, Flash memory Power supply are the different components in the Cisco Router.

Each memory performs different operators in the Cisco router. To connect the network, with the different protocols. We can also call it the hardware device that connects the two different networks. The data can be transmitted in the form of packets from one device to the other.

A cross cable connection is maintained in the connection between the two networks. We call the wide-area network the serial ports. At the different data rates, the local area network transmits the information from the sender to the receiver.

Second Explanation of Cisco Router Memory

Different Types of Router Memory

There are different types of memory contained in the Cisco router that provide the storage and required dynamic caching. There are following Different Types of Cisco Router Memory: FLASH, NVRAM, DRAM, ROM that have a different task to perform in the router.


ROM stands for Read-Only Memory. It is types of memory in a Cisco router that is available in the router’s processor board. The bootstrap program or the software that runs on starting the Cisco router is usually stored in the Read-Only Memory (ROM). Rom also maintains its instructions for Power on Self Test diagnostics.

There are basically four basic functions that are performed here as follows:

POST– Power on Self Test. It is work just like normal computer work, on starting the computer they make sure all the components are working or not. Similarly, your router do the same things, it checks the CPU, the amount of DRAM and flash installed, and all the interfaces. If any modules that you may have installed will be also checked at this time

Bootstrap– The bootstrap program start the CPU and initialize the boot process of the router by locating and loading the IOS.

RxBoot– The RxBoot is also known as the Mini-IOS. This is used when your IOS is corrupted and your flash simm is blank and needs to have a version of IOS installed. The Rxboot loads and gives you limited functionality to configure and set up so you can load a new version of IOS on your flash simm.

ROM Monitor– This is a mode on the Cisco router that allows you to diagnostics or loading IOS images on the console session. If you have any problem with router configuration suppose you want to reset the password or something else then you can go into the diagnostics mode by just pressing the key CTRL + Break on the keyboard.

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DRAM is the short form of Dynamic Random Access Memory. Dynamic Random Access Memory is similar to the RAM that you used in the Computer. It provides the temporary storage of information such as it holds the current configuration routing table which are going to be used or which are using by the Cisco router. The RAM also hold the current running until you do not save that into the NVRAM as the configuration stored in the NVRAM are not erased even on power down but in the case of RAM, all the configuration of the router are erased when the power of the router goes off.

It is divided into two parts. The first part of the DRAM is the main processor area. In this area, you store the running configuration of the router, a routing table, and any ARP tables are stored in this area.

The second part of DRAM Memory is the shared Input/Output Memory area where you store the data and the packets that are being routed by the router. If the router processor has more capability to handle the request, the data packets will fly right through. But when your router’s processor overwhelmed with data packets and thus need to buffer them in this area of memory. Finally, this memory can be upgraded to a larger size by either putting it in a larger DRAM stick or if the router has an additional DRAM slot then it can put into that slot.


This memory is also known as the EPROM (Erasable Programming Read Only Memory). In this memory, the information stored in the Flash of the Cisco router is not vanished or erased when you off the power of the Cisco router. This is the memory where store the Cisco Router’s IOS. You can upgrade your IOS by downloading the latest version of the IOS and if you want to erase this then you can also do this.


NVRAM is a Non-Volatile Random Access Memory which stores the startups running configuration on the router’s NVRAM will not be erased when you turn off the power of the router. You can copy the running configuration of the router into the NVRAM to save your configuration. The main thing in the NVRAM is that it retains the information that it holds even if the power of the router is off which is very useful considering you won’t have to reconfigure the router every time the power goes off.

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