Joining filesystems with "mount"

Nomenclature clash: "the filesystem" usually refers to the complete set of mounted disk partitions forming a filesystem tree, "a filesystem" refers to the filesystem in a specific disk partition, and has:

• An inode table (which determines a maximum number of files that can be allocated)
• A filesystem root directory (with a standard inode number)
• And then maybe a bunch of files and subdirectories
• File allocation is on a per-filesystem basis
• Hard links can refer only to files in the same filesystem

Multiple filesystems are joined into the directory tree by "mounting"

• The mounted filesystem's root directory becomes a subtree of an existing directory in an already-mounted filesystem
• The filesystem root directory is mounted by the OS kernel at boot time and its disk partition specified as a configuration parameter
• When mounting, the device node for a disk partition identifies the filesystem, i.e. mount /dev/hda5 /var

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