Transfered from Linux Config:
Question:
Why is the GNU/Linux filesystem referred to as hierarchical?
Answer:
GNU/LINUX system does not have so-called drives with assigned letters as it can be seen in MS Windows environment. Instead hard drive can by mounted ( connected ) to any directory within an entire file system. On the top of the file system hierarchy structure is a root directory represented by “/” which expands to sub-directories forming hierarchical tree.
Further reading:
File system basics