.H3 "Directories"
Directories are a special kind of file containing lists of files names and file
numbers.  Think of an old-fashioned folder in which you store paper documents.
You might have a number of separators with tabs separating various kinds of
documents.  You may write a description of the content on these tabs.  In this
case, the tabs form the directory for the folder.  Many systems use this concept
for directories.
.P
On the other hand, it's possible that your tabs are too small to write anything
useful on them.  Many offices use a system where each tab only has a number on
it.  At the beginning of the folder there's a sheet of paper saying something
like:
.TS
tab(#) ;
r | lw49 .
Tab#Content
_
1#House plans
2#Letters
3#Tradesmen
4#Air conditioning
5#Personal documents
3#Furniture
_
.TE
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This may not seem like much of a difference, but there are some significant
advantages:
.Ls B
.LI
You can write a more detailed description on the sheet.
.LI
It's easier to read what's in the folder: the information is all in one place.
.LI
You can write multiple entries.  Looking back at the table, you'll note that
there are two entries for tab 3.
.Le
This is the approach that UNIX uses.  The description is what we call the file
name, and the separator is what we call an \fIinode\fP.  The number of the tab
is the \fIinode number\fP.  In UNIX, you'd find some information on the
separator itself, for example when it was last updated and who can look at it.
The connection between the name and the tab is called a \fIlink\fP, sometimes
called a \fIhard link\fP, though this term tends to hide the real relationship
between the file and its name.  Note in particular that no one name is more
important than the other.  It's helpful to think of this model when considering
file systems.
