Cisco 1600 - Manual (Page 8)

Based on the configuration register value in Non−Volatile RAM (NVRAM), the router either stays in
ROMmon, or RxBoot is executed from Boot ROM.
RxBoot analyzes the hardware. Based on the configuration register value, the router either stays in
RxBoot, or the Cisco IOS software image file (default, or as defined in the startup configuration) is
executed from PCMCIA Flash or RAM (or moved there from the network). This main Cisco IOS
software image analyzes the hardware again.
The router configuration file, which is stored in NVRAM, can contain boot system commands. For
example, boot system flash slot0:c1600−sy−l.122−1a.bin.
This forces the RxBoot to look for the c1600−sy−l.122−1a.bin file on the Flash device called "slot0:".
The boot system directive in the router configuration file overrides the configuration register. If there
is no boot system statement, and if the configuration register is at its default value, the RxBoot grabs
the first file it finds in its Flash. If that fails, it tries to load an image from boot ROM.
2.
The Cisco IOS software creates some data structures such as Interface Descriptor Blocks (IDBs) in
the main processor memory, carve interface, and system buffers on shared input/output (I/O) memory,
and loads the startup configuration. RxBoot also performs these functions, but it does not re−analyze
the hardware unless the full Cisco IOS software is executed.
Figure 8 Sequence of Operations
Here is an example of this platform booting from Flash:
3d08h: %SYS−5−RELOAD: Reload requested by console.
System Bootstrap, Version 11.1(7)AX [kuong (7)AX], EARLY DEPLOYMENT RELEASE
SOFTWARE (fc2)
Copyright (c) 1994−1996 by cisco Systems, Inc.
3.
Cisco − Cisco 1600 Series Router Architecture