5.1 The File System
5.1.3 File system structure
The structure of the file system is a hierarchy which looks like an inverted or upside down tree with the root at the top. It is common for directories to have subdirectories. This is similar to having a file drawer called Projects (directory) containing folders in it with the names of individual projects (subdirectories). Directories can contain subdirectories and files. Subdirectories can also contain additional subdirectories and more files. All operating systems have some sort of directory structure to organize information on their hard disks. With some operating systems such as Windows and MacOS, directories are referred to as folders. With the UNIX file system, they are called directories but are used in the same manner.

Figure shows a hierarchical directory structure as an inverted tree. A common hierarchical system or structure we are all familiar with is the family tree of our ancestors. The file system directory structure is similar to a family tree. With the exception of the root directory, each directory in the hierarchy has a parent directory and most will have child directories which are referred to as subdirectories. The root directory is always at the top of the hierarchy and is designated as a forward slash (/).

Each child directory is contained in a parent directory. This is similar to having a set of file folders where each folder (directory) has a folder inside (subdirectory). The location of a file or directory in the tree can be specified by naming each directory you have to go through to access it. A fully qualified file or directory name is also known as an absolute pathname and includes the names of all parent directories above it. For example, to determine the location of the notes document, we must name all folders above it.