ROM: Read Only Memory. bootstrap startup program. operating system software. power on diagnostic test program.
POST: Power On Self Test
Flash Memory: ios image here. erasable reprogrammable rom.
RAM: Random Access Memory. stores operational info such as routing/switching tables and running config file. it is lost when router powered down or rebooted.
NVRAM: non volatile ram. holds router startup config file. contents are not lost on rebooting. NV(never)
