File System And Mount Points

The 'single file tree' concept - Unix systems place all file systems spanning all devices/partitions, into one large files tree.

To mkdir is human - to mount - divine. In order to make a file system's contents accessible, it needs to be mounted on a directory in the current files tree. Only the 'root' user may mount a file system.

The umount distortion and the case of the stuck CD - a file system may be unmounted (using 'umount') only if no process is holding any of its files open.