Data Facility System-Managed Storage (DFSMS) manages the data sets used for processing the hierarchical file system which is z/OS. These data sets make up a file hierarchy which consists of files and directories.

• Files contain data or programs. A file containing a load module or shell script or REXX program is called an executable file. Files are kept in directories.
• Directories contain files, other directories, or both.

Additional local or remote file systems can be mounted within the file hierarchy.