- Dynamic Random Access Memory (DRAM) -- Data stored in DRAM on the Cisco router will be lost when the Cisco router power off or reload. This memory have two sections. The section in the Main Processor area will store the router's running configuration, routing tables and ARP tables. The section in the Shared Input/Output Memory area will act as a buffer when the router is overwhelmed with data packets.
- Flash -- The information stored in flash memory will not lose when the router power off. The router's IOS is stored here. You can download a different version of the IOS and load it to the flash memory. This memory can be easily upgraded to a larger size by either putting a larger flash memory in the router or adding additional flash memory if multiple slots are avialable.
- Non-Volatile Random Access Memory (NVRAM) -- What is stored in will not lose when the router power off or reload. Compared to DRAM and Flash, the NVRAM is generally small, with KB size. It is used to store the router's configuration file. Notice when you configure the router, the running-config is stored in DRAM. If you don't want to reconfigure the router every time you power up the router, you have to save the running-config to the startup-config which stores in NVRAM.
- Read Only Memory (ROM) -- This is where the router reads the microcode to start the boot process and basic self checks. ROMMON, a low-level operating system normally used for manufacturing testing and troubleshooting is also stored in ROM.
Cisco Router Memory
The Cisco switch and router have four types of memory: ROM, DRAM, NVRAM, And Flash.