Important Router Parts

1.ROM - Read Only Memory.
This is a form of permanent memory used by the Router to store:
The "Power-On Self Test" that checks the Router on boot up.
The "Bootstrap Startup Program" that gets the Router going.
A very basic form of the Cisco IOS software.
(to change the ROM you have to remove and replace chips)

2.Flash Memory
An Electronically Erasable and Re-Programmable memory chip.
The "Flash" contains the full Operating System, or "Image".
This allows you to Upgrade the OS without removing chips.

3.NVRAM - Non-Volatile RAM
This stores your Router's "Startup Configuration File".
Similar to Flash memory, this retains data even when power is lost.

4.RAM - Random Access Memory
This is regular computer memory chips.
These are the working memory of the Router,
and provide Caching, Packet Buffering, and hold Routing Tables.
The RAM is also where the Running Operating System
lives when the Router is on.
RAM loses all its data when reset or powered off.

5.Interfaces - Where the Router meets the Outside World.
Basically your Router will have Serial interfaces,
Which are mostly used to connect long-distance as in a WAN (Wide-Area Network).
You will also have LAN (Local-Area Network) Interfaces,
such as Ethernet, Token Ring, and FDDI (Fiber Distributed Data Interface)