A ``filesystem'' is a distinct division of the operating system, consisting of files, directories, and the information needed to locate and access them.
Filesystems can reside on local hard disks, CD-ROMs, and floppy disks. You can also mount remote filesystems on your local system and make local filesystems available for other systems to mount. See ``Exporting and unexporting filesystems'' and ``About mounting and unmounting NFS filesystems''.
Each UNIX system has at least two filesystems on the primary hard disk. The main filesystem is called the ``root'' filesystem (also known by the symbol ``/''). The root filesystem contains the programs and directories that comprise the operating system. On small hard disks, the root filesystem also includes all the user directories. The second filesystem is called /stand and contains the information needed to boot the system, the boot program and the kernel, /stand/unix.
The primary hard disk can be divided into more than these two filesystems. See ``The installation and upgrade procedure'' for information about dividing the hard disk at installation time. Dividing the primary hard disk into multiple filesystems protects the data and makes maintenance easier. The most common division is the /u or /home filesystem, used for user accounts. Keeping user accounts separate from the root filesystem makes backing up your system much easier. Because system data changes less frequently than user data, you can back up the /u or /home filesystem more frequently than the / (root) filesystem. See ``Backing up filesystems'' for more information.
The system administrator creates the filesystems on the hard disk, then mounts and unmounts -- attaches and detaches -- the filesystem when needed, similar to the way you access a floppy disk.