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<title>What is a Directory Tree?</title>
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<h2>What is a Directory Tree?</h2>
<p>On most computer operating systems, so on Microsoft Windows, the data on the
hard disk are organized hierarchically.
</p>
<p>On the one hand there are the <i>files</i> which have a certain size and contain
the effective data. Each file has a name. Under Microsoft Windows the "filename
extension" informs about the type of the file. The extension ".exe", for
instance, indicates that it's a program file. The extension ".doc" indicates a
WinWord document, ".jpg" is a photo, and so on. But ridiculously the Microsoft
Windows Explorer hides these filename extensions by default. You can change
this behaviour in the options menu of the Windows Explorer.
</p>
<p>On the other hand there are <i>directories</i>. The Windows Explorer and
WinDirStat, too, symbolize directories as yellow folders. Directories also
have a name, but normally without a filename extension. Directories only serve
to contain files and other directories ("sub-directories"). Due to the fact
that directories can contain subdirectories, and those again can contain
subdirectories, the result is a hierarchical structure on the disk.
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<img src="tree.jpg" width="99" height="105" align="left" vspace="20" hspace="20" />
Instead of "hierarchical structure" we simply say <i>tree structure</i>. Since
a tree is built hierarchical as well: The trunk branches out into branches, the
branches into sub-branches, twigs and finally into the leafs. In a file system
the so called root directory is the trunk, the directories
are the branches and the files are the leafs.
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<p>
That's why we call the file system of a computer simply a "directory tree".
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<p><br clear="all" />
Unlike most real trees, on a disk the trunk and the branches already have
leafs. And, unlike most real trees, too: the <u>files</u> are the voluminous
entities (the size of which is mesured by megabytes or gigabytes), whereas the
actual directories are neglectibly small. By the way, we imagine abstract trees
as turned round: the root at the top, the leafs at the bottom.
</p>
<p>If you saw a branch off a tree and stick it into the earth, then it becomes
itself a little tree (well, at least it looks like one): Every branch is,
together with its sub-branches and leafs, itself a tree, a <i>subtree</i>.
</p>
<p>The family tree metaphor is often used as well: The subdirectories and files of
a directory are called its <i>children</i>. And a directory containing a
subdirectory or file is called their <i>parent</i>. The root directory is
earliest ancestor of all items in the directory tree.
</p>
<p>A <i>path</i> like "C:\documents\letters\draft\loveletter.doc" indicates that on
the hard disk C:, in the root directory "C:\" there is a directory "documents",
under it the subdirectory "letters", under it a subdirectory "draft" and in
there a file "loveletter.doc". So the path is a precise representation of the
way from the root to the leaf.
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