Because the super-block contains critical data, newfs replicates it to protect against catastrophic loss. The default super block always resides at a fixed offset from the beginning of the file system's disk partition. The redundant super blocks are not referenced unless a head crash or other hard disk error causes the default super-block to be unusable. Within the file system are files. Certain files are distinguished as directories and contain collections of pointers to files that may themselves be directories.
Every file has a descriptor associated with it called an inode .
The inode contains information describing ownership of the file, time stamps indicating modification and access times for the file, and an array of indices pointing to the data blocks for the file. The inode structure may also contain references to indirect blocks containing further data block indices. The size of file system blocks can be any power of two greater than or equal to 4096. The block size of the file system is maintained in the super-block, so it is possible for file systems of different block sizes to be accessible simultaneously on the same system. Associated with the super block is non replicated summary information .