It’s probably a good idea to explain a little theory before
discussing the mechanics of using disks. In particular, you must
understand the concept of a _filesystem_. This can be a bit
confusing because it has several meanings.
_The_ filesystem refers to the whole directory tree, starting with
the root directory /, as described in earlier chapters.
A filesystem in general means any organization of files and
directories on a particular physical device. “Organization” means
the hierarchical directory structure and any other information about
files one might want to keep track of: their size, who has
permission to change them, etc. So you might have one filesystem on
your hard disk, and another one on each floppy disk.
“Filesystem” is also used to mean a _type_ of filesystem. For
example, MS-DOS and Windows 3.1 organize files in a particular way,
with particular rules: Filenames can have only eight characters, for
example, and no permission information is stored. Linux calls this
the msdos filesystem. Linux also has its own filesystem, called the
ext2 filesystem (version two of the ext filesystem). You’ll use the
ext2 filesystem most of the time unless you’re accessing files from
another operating system or have other special needs.
Any physical device you wish to use for storing files must have at
least one filesystem on it. This means a filesystem in the second
sense—a hierarchy of files and directories, along with information
about them. Of course, any filesystem has a type, so the third sense
will come into play as well. If you have more than one filesystem on
a single device, each filesystem can have a different type—for
example, you might have both a DOS partition and a Linux partition
on your hard disk.