Routers: The IOS and Its User Interface

Before examining the IOS, a review of hardware and hardware terminology is useful. This
section of the book reviews common hardware details.

Most Cisco routers have a console and an auxiliary port. All Cisco routers have a console port,
which is meant for local administrative access, from an ASCII terminal or computer using a
terminal emulator. The auxiliary port, missing on a few models of Cisco routers, is intended for
asynchronous dial access from an ASCII terminal or terminal emulator; the auxiliary port is
often used for dial backup.
Each router has different types of memory as follows:

• RAM
—Sometimes called DRAM for
dynamic
random-access memory, RAM is used by
the router just like it is used by any other computer—for working storage.
• ROM
—This type of memory stores a bootable IOS image, which is not typically used for
normal operation. ROM does contain the code that is used to boot the router until the
router knows where to get the full IOS image.
• Flash memory
—Either an EEPROM or a PCMCIA card. Flash memory stores full
function IOS images and is the IOS default for where the router gets its IOS at boot time.
Flash memory may also be used to store configuration files on Cisco 7500 series platforms
(
copy config flash
).
•
NVRAM
—Nonvolatile RAM stores the initial or
startup
configuration file.
All of these types of memory are permanent memory except RAM. There is no hard disk or
diskette storage on Cisco routers.

The processors in the routers vary from model to model. Although they are not specifically
listed as requirements for the CCNA exam, some reference to terminology is useful. In most
routers, the model number you order or own implies the processor speed; you would not then
order a specific processor type or card. The exception to this is the 7000, 7200, and 7500 series
of routers, for which you choose either a Route Switch Processor 1 (RSP-1), RSP-2, or RSP-4.
In any case, the 2500 series, 3600 series, 4000 series, and 7xxx series all run the IOS. This
commonality allows Cisco to have exams, such as CCNA, that cover the IOS features without
having to cover many hardware details.
Interfaces are used by a router for routing/bridging packets/frames through a router. The types
of interfaces available change over time due to new technology. For example, packet-over-
SONET and voice interfaces are relatively recent additions to the product line. However, some
confusion exists about what to call the actual cards that house the physical interfaces.