A hierarchical file system consists of:
- Files, which contain data or programs. A file containing
a program object, shell script, or REXX program is called an executable
file. Files are kept in directories.
- Directories that contain files, other directories,
or both. Directories are arranged hierarchically, in a structure that
resembles an upside down tree, with root directory at the top and
the branches at the bottom. The root is the first directory
for the file system at the peak of the tree and is designated by a
slash (/).
- Named pipes, links, and other UNIX items,
such as character special files like /dev/console that are used by
applications like syslogd. See z/OS UNIX System Services Planning for more information about UNIX items like character special files.
The term
file system has all of the following meanings:
- A logical collection of files, directories, named pipes, links,
and other UNIX items and metadata
that are arranged in a hierarchy.
- A particular instance of a logical collection of these items that
are arranged in a hierarchy. They might be on local or remote disks
or in computer memory.
- A program that is designed to provide the functions and data of
one type of file system.
The context indicates which meaning is intended. Often more than
one meaning is intended; this is an industry convention.
To the z/OS® system, the
file hierarchy is a collection of file systems. Additional instances
of local or remote file systems might be mounted (logically connected)
on directories of the root file system or of additional file systems.
Several types of file systems are supported by z/OS, including the following file systems:
- z/OS File System
Each
instance of z/OS File System
is in a linear data set.
- HFS (hierarchical file system)
Each instance of HFS is in an
HFS data set.
- TFS (temporary file system)
Each instance of TFS is in computer
memory.
- NFS (Network File System)
NFS server provides access to file
systems that are on other computers.
For most application programs, these types of file systems are
interchangeable. The root file system is the first file system that
is mounted. Subsequent file systems can be logically mounted on a
directory within the root file system or on a directory within any
mounted file system.