Hi Yang,
Please find the details below:
NVRAM:- NVRAM is used for writable permanent storage of the startup configuration. This is where the configuration is saved when you type copy run start..
ROM: ROM stands for Read-Only Memory. ROM stores the router’s bootstrap startup program, operating system software, and power-on diagnostic test programs (the POST).
Flash:This is where the IOS is stored. Before upgrading you should check if the flash is big enough to hold the old and the new images or that you have to delete the old one before downloading the new one.
If I understand your question correctly the firmware =software, this is the one required to have your switch working and booting up. After which all the other show will be performed on the box.
HTH
Regards
Inayath
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