The filesystem

All files in a Unix system are part of a tree
No system can exist without a file system
It's a single tree, even if you have many disks
Everything (well, almost) is seen like a file
               /bin
               /etc
               /dev
               /home
               /lib
               /mnt
               /usr
               /usr/bin
               /usr/lib
               /proc
               /sys
               /sbin
               /tmp
               /var