When you configure a switch, it needs to use the configuration. It also needs to be able
to retain the configuration in case the switch loses power. Cisco switches contain randomaccess memory (RAM) to store data while Cisco IOS is using it, but RAM loses its contents
when the switch loses power or is reloaded. To store information that must be retained when
the switch loses power or is reloaded, Cisco switches use several types of more permanent
memory, none of which has any moving parts. By avoiding components with moving parts
(such as traditional disk drives), switches can maintain better uptime and availability.
The following list details the four main types of memory found in Cisco switches, as well as
the most common use of each type:
■ RAM: Sometimes called DRAM, for dynamic random-access memory, RAM is used
by the switch just as it is used by any other computer: for working storage. The running
(active) configuration file is stored here.
■ Flash memory: Either a chip inside the switch or a removable memory card, flash memory stores fully functional Cisco IOS images and is the default location where the switch
gets its Cisco IOS at boot time. Flash memory also can be used to store any other files,
including backup copies of configuration files.
■ ROM: Read-only memory (ROM) stores a bootstrap (or boothelper) program that is loaded when the switch first powers on. This bootstrap program then finds the full Cisco IOS
image and manages the process of loading Cisco IOS into RAM, at which point Cisco
IOS takes over operation of the switch.
■ NVRAM: Nonvolatile RAM (NVRAM) stores the initial or startup configuration file that
is used when the switch is first powered on and when the switch is reloaded.