A file is a one-dimensional array of bytes with no other structure implied. Information about each file is stored in structures called inodes (inodes are described in the next section "Inodes"). Files cannot span filesystems.
A directory is a container that stores files and other directories. It is merely another type of file that the user is permitted to use, but not allowed to write; the operating system itself retains the responsibility for writing directories. Directories cannot span filesystems. The combination of directories and files make up a filesystem.
The starting point of any filesystem is an unnamed directory that serves as the root for that particular filesystem. In the IRIX operating system there is always one filesystem that is itself referred to by that name, the Root filesystem. Traditionally, the root directory of the Root filesystem is represented by a single slash (/). Filesystems are attached to the directory hierarchy by the mount command. The result is the IRIX directory structure shown in Figure 3-1.
Figure 3-1 : The IRIX Filesystem You can join two or more disk partitions to create a logical volume. The logical volume can be treated as if it were a single disk partition, so a filesystem can reside on a logical volume and hence is the only way for a single filesystem to span more than one disk. Logical volumes are covered beginning in Chapter 6, "Logical Volume Concepts."
The following subsections describe key components of filesystems.