Dirty Rectangles

Hi all,
Can anyone explain the concept of "Dirty Rectangles" and how it can be used to speed up graphics,
Where can I find more about it?
Thanks and have a nice weekend.

The concept of dirty rectangles is that when you update the screen you only change what has changed since the last frame was displayed. Therefore it should be faster because your not painting as much. Remember don't clear the back buffer tho.
Just do a search on google to find out more.

Thanks, Electroman. And now all is left is to figure out how I can
implement this technique using bitblt or other APIs.