Why do we need MVP Architecture

Question

Hi,

If MVC - Model, View, Controller. Where View is the Presentation layer(.aspx file), Controller responds to the User interactions (Event handlers such as button_click in .aspx.cs file) and Model(Dataset/DAL etc).

Then can some once please explain the below:
           1. What is MVP, and how it is different from MVC
           2. When do we use
           3. And most importantly what is its corellation to physical files (aspx/aspx.cs/DAL etc)

Thanks in advance

Rakesh