In Unix / Linux (as opposed to MS Windows), there are no drive letters (such as '''C:''', or '''D:'''). All files and directories appear under a single ancestor directory called the "'''root directory'''".

In the Linux (Unix) OS, the "'''root directory'''" / is the starting directory, and other "''child directories''", "'''grandchild directories'''", etc. can be created as required. The hierarchical structure resembles an "''upside-down tree''". There is actually a command called '''tree''' that displays a "'''directory tree diagram'''"!