Unix Vs. DOS

[Musa J. Jafar]

Hello there. I am reading about the
unix file system and the dos file system(sort of speak)
Unix is a real Hierarchy while DOS is not
This is what I understood from my readings.
But DOS looks like a hierarchy.
questions:
Why DOS is not real?
What is the advantage of UNIX over DOS in a single user Env.
     other than you have more options under Unix (but you pay for them)

Thanks
Musa.