Different Types of Router Memory: FLASH, NVRAM, DRAM, ROM

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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