I have done some reading about Cisco Routers and Switches main components, such as ROM/RAM/NVRAM/FLASH, it is a little bit confusing. I wonder if there is an Expert out there to clarify the function sequences of these components. For instance I will go through boot sequences the way I understand it and please correct me if I am wrong:
when a router/switch boots up:
1- The ROM will check the functioning of CPU/RAM, and the rest of the hardware ...
This is called boot strap..
2-IOS will be loaded from RAM if it has been initially used and uncompressed, otherwise it will be loaded from Flash and will uncompress it and store it in RAM.... However I have read that the contents of RAM gets lost when the router is powered off, so why does it look in RAM to load the IOS during the boot process ????
Does that mean powering off then powering on the device will purge the RAM, but reload the device will not ?
by the way, the Running config is stored in RAM, I am not sure either if it is lost when the router is reloaded.
3- NVRAM stores the Start-up config... the configuration that has been saved from running config
4- Flash : will be used only if the router has been in power off state. I mean it is not a Reload but it is after Power off then Power On.
Any clarification will be very much appreciated