Filesystem
A filesystem (or file system) is a computer’s method of controlling how data is locally stored and retrieved. All computers have a filesystem, although the specific system each uses depends on the particular operating system.
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You can view the file systems of a Cisco IOS device with show file systems
Types
There are several filesystem types:
disk: storage devices such as flash memoryopaque: used for internal functions, these are not discrete physical devices, but rather logical internal systemsnvram: Non-Volatile RAM; startup-config is stored herenetwork: external filesystems, such as TFTP servers