Different types of memories are being used in a CISCO router. They are:

• Random Access Memory (RAM): RAM used in a router is the same as the RAM that is installed in our Mobile Phones, Laptops, and PCs. The RAM will be divided into two AREAS:
  • Main Processor Memory: It stores the information that belongs to the routing table, running router configuration, and ARP (Address Resolution Protocol) cache.
  • Shared I/ry: It is a temporary storage memory where the queued data packets will be stored.
    When the router gets restarted or rebooted, all the information stored within the RAM will be deleted(that is why it is considered as Volatile memory). We can store the data permanently using NVRAM.
• Non-Volatile Random Access Memory (NVRAM): NVRAM is useful in STORING the start-up configuration FILE which are copies of the CISCO Router Configuration file and will be retained even after rebooting or restarting of router OCCURS. In this, the data will not be lost and can be easily recovered by rebooting or switching off the router. If you want to permanently save the running configuration files, these files should be moved from RAM to NVRAM.
• Read-Only Memory (ROM): The boot procedure of a CISCO router will begin from the ROM memory section. ROM will have programming instructions such as Bootstrap program and POST (Power-On-Self-Test). POST test is useful in verifying whether hardware components like RAM, CPU, and interfaces are properly working or not. If they are not functioning properly, an error message will be sent by POST. After this, for setting up the CPU and boot functions of the router, the bootstrap application is used. The bootstrap program will be in charge of finding and loading the operating SYSTEM (IOS) of the router. All this information will be saved or stored inside the ROM and the data will be retained even after switching off or rebooting the router.
• Flash Memory: It is an EPROM (Erasable Programmable Read-only Memory) chip that is more cost-effective for enterprise environments. The router operating system i.e., IOS (Internetwork Operating System) will be available in flash memory. It can be easily upgradable and does not need any hardware changes. Also, the content in flash memory will be retained when the router is switched off or rebooted.