Data and programs are stored, as in other operating systems, the files stored on magnetic disks. Each disc can be divided, logically, in more areas called partitions. Partition size is determined by the system administrator to install your system or insert a new disk when the system. Each partition is managed separately from the operating system such as a device-independent.
To manage files in a partition, the operating system must have information about: free data blocks in the partition, data blocks occupied, information about every file containing that partition. All information and organization of files must be in the partition that created the file system. During its evolution, in Unix systems have been defined more files, they differ in size blocks of data, and information contained in data structures used to manage files. Examples of file systems: S5 (UNIX System V), UFS (BSD Unix), RSF and NSF (computer networks).
To achieve coexistence of several different file systems, operating system kernel contains a particular level, called virtual file system, being designed to equalize access to files. Operations with files received calls from users are handled at this level, the call depending Customize file system where the file is called.
File in the Unix sense notion:
Unix file is considered as a sequence of bytes, with an end of file mark. There are three types of files:
• Regular files 
• File manager
• Special files
A regular file is used for storing information on magnetic media, it may contain a source program (text) or a form executable code (binary) and data necessary for the execution of programs. Regular files are the only type of files used to store long term information. File names can not exceed 14 characters printed in older Unix systems and 255 characters in later. Allowed characters are case-sensitive English alphabet, numbers and _ sign. Uppercase and lowercase letters are considered distinct. Sometimes it is necessary to have a filename extension: shell program/ bass for Basic programs. C for C programs, etc.
Directories are files containing subdirectories and files contained information about. Special files are files associated peripheral devices. Users can make the peripheral data exchange without having to know details about their operating mechanism.
