NVRAM - how does it work

Its some Flash memory that gets memory mapped into the address space of the processor and read by ROMMON as it boots.

The memory maps are very different per platform.

Maybe get the dynamips emulator, and study how it starts up an IOS image?

Does it mean, that every configuration part like "Boot system" can be found in a defined E/O register and is simple activated with a kind of flag while the configration is entered? I'm thinking because the most of the configuration file ist read after the IOS has been loaded.

I don't know the dynamips emulator. I will take a look at it.

Thanks a lot so far

Oli

Depends on the platform..

Switches tend to have an environmental variable for the boot drive that will get updated when you do the 'boot system' in the config. On the very rare occassion, this can get messed up and you may have to set it manually (at least I've had to on two older switches). ROMMON environmental variables get stored in yet another area of flash: You can see these from ROMMON on switches.

Routers don't do this, but instead seem to parse the full config for the 'boot system' commands and act appropriately. Again, poke around in ROMMON and you won't find the boot env variable the same as in a switch.