Each of these disk partitions may contain one file system. A file system never spans multiple partitions. Within the file system are files. Certain files are distinguished as directories and contain pointers to files that may themselves be directories.
Every file has a descriptor associated with it called an inode .
An inode contains information describing ownership of the file, time stamps marking last modification and access times for the file, and an array of indices that point to the data blocks for the file. An inode may also contain references to indirect blocks containing further data block indices. A 150 megabyte traditional UNIX file system consists of 4 megabytes of inodes followed by 146 megabytes of data. The allocation of data blocks to files is also suboptimum. The traditional file system never transfers more than 512 bytes per disk transaction and often finds that the next sequential data block is not on the same cylinder, forcing seeks between 512 byte transfers.