Router Memory - Cisco 1603R User Manual

Router Memory

The Cisco 1600 series routers are either of run-from-flash (RFF) or run-from-RAM (RFR)
models. Router model names with an R are RFR routers; all other models are RFF. In this
document, model names without an R refer to both RFF and RFR models, except where
noted. This section describes the two memory architectures used in the Cisco 1600 series
routers.
Run-From-Flash Architecture
With RFF, the microprocessor uses the uncompressed Cisco IOS software image that is
stored in Flash memory. The software image runs directly from Flash memory. RAM stores
working data such as Cisco IOS data structures, network routing tables, and packets to be
transmitted to and received from network interfaces.
The running software image cannot be used to download new software to Flash memory
because it would attempt to overwrite itself. (However, when you are using Dual Flash
Bank memory, you can download the new software image into a different Flash memory
partition.)
To download a new software image without using Dual Flash Bank memory, a boot-helper
image (called XBOOT) has been added to the ROM on the RFF models. The boot-helper
image is a small subset of Cisco IOS software that supports only a subset of the interfaces
and the WAN protocols. RFF ROM supports the following WAN interfaces. (These are all
onboard interfaces, not WAN-interface-card interfaces.)
•
Serial (synchronous and asynchronous) (Cisco 1601)
•
DSU/CSU (Cisco 1602)
•
ISDN S/T (Cisco 1603)
•
ISDN U (Cisco 1604 and Cisco 1604 R)
When upgrading the Cisco IOS software in Flash memory, you must boot the router from
the ROM image. The Flash memory can be overwritten because the Cisco IOS software
that is stored in Flash memory is not being used to run the router.
Router Memory
Overview of the Router 1-7