Every file that is created in Unix has correspomding Inode (information node).
Inode is data structure on disk that contains information about file or directory.

It indicates physical location or data blocks. It does not contain names of files, but
contains ownership information & permission details includes - file type, file size,
last accessed, modified when inodes themselves were last modified. When File is
created some inodes are allocated to it.

Partially allocated Inodes means inode isn't formatted correctly, thsi may happen
because of hardware failure.

Number of files in filesystem can't exceed its number of inodes. To modify this
number you have to reinitilaize this filesystem. Filesystem can run out of inodes
if there are too many small files in filesystem.

Every inode has identifying number caled i-number. To display files i-number use
"ls -i" command.
Inode number identifies data block address for it.
-> ls -i filename1 = inode number of filename1
-> ls -il = full directory listing including inode i-number.

An i-number is unique within a given filesystem.
So you can have same inode on different devices.

Every directory entry keeps track of two pieces of information about a file; filename
and inode number associated with that file.