Unix File System

Before playing around with the Unix commands, Its essential to understand the Unix file system. Unix treats every thing it knows and understands, as a file. All utilities, applications, data in Unix is stored as files. The Unix File system resembles an upside down tree. Thus the file system begins with a directory called root. The root directory is denoted as slash (/). Branching from the root there are root directories called bin, lib, etc, tmp and dev. The root directory also contains a file called Unix which is Unix kernel itself. These directories are called the sub-directories, their parent being the root directory. Each of these sub-directories contains several files and directories called sub-sub-directories.
The main reason behind the creation of directories is to keep related files together and separate them from other group of related files. For example, it is good idea to keep all user related files in the usr directory, all device related files in the dev directory, all temporary files in the tmp directory and so on.