ROM is read-only memory
available on a router's processor board. The initial bootstrap software that
runs on a Cisco router is usually stored in ROM. ROM also maintains
instructions for power-on self test (POST) diagnostics. For ROM Software
upgrades, the pluggable chips on the motherboard should be replaced.
Flash
Memory
Flash memory is an
Electronically Erasable and Re-Programmable memory chip. The Flash memory
contains the full Operating System Image (IOS, Internetwork Operating
System). This allows you to upgrade the OS without removing chips. Flash
memory retains content when router is powered down or restarted.
RAM
RAM is very fast memory
that loses its information when the system is restarted. On a router, RAM is
used to hold IOS system tables and buffers. RAM memory is basically used for
all system operational storage requirements. RAM Stores routing tables, Keeps
ARP cache, Performs packet buffering (shared RAM) and RAM Provides temporary
memory for the router configuration file of the router while the router is
powered on.
NVRAM
(Non-volatile Random Access Memory)
NVRAM is used to store
the startup configuration. This is the configuration file that IOS reads when
the router boots up. It is extremely fast memory and retains its content when
the router is restarted.
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