How to structure the admin zone

[eluser]Dagobert Renouf[/eluser]
Hello guys,

As I was playing a bit with my very first Codeigniter app, I ran into a logical problem, how do I structure the admin zone ?

I searched a bit and found out you guys insert directly into the page controller an admin function, and I don't see the logic in there.

I'm thinking about the url like this : website/index.php/admin/ nothing more.
So I have to create some admin folder with a controller for each part of the site I want to be able to admin, am I right ?

How do I manage to create an admin zone clearly separated from the rest of the site as I explained ? And if you think I'm not seeing things as I should, why ?