how can a utility like **find** command  can map an inode number to a filename?

 i mean if we pass **find -inum inode_number  / **   , it will show us the  files associated with that "inode_number". What is the underlying mechanism used in all this ?

 I have peeped into the findutils code but it seems horrible to figure it out from that code .:)

thanks in advance.
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