Difference between Web and Application Server!

Hi all,
I am a beginner in Java and I would like to know the answer of foll.
questions:

Can anyone tell me

1. what is the difference between an Application server and a Web Server?
2. Which one of them have to be used where?
3. Advantages of one over another?
4. Where can I find good topics on these?

Your reply will be greatly appreciated.
Thanks

Hello
Application Server is the middle tier component between the client and the 'real' server . Application server stores all the business logic .
Use the web server when you want to have a server on the world wide web and use an application server in any multi tier architecture to store the business logic so that u get a thinner client, better maintenance, OO design etc. etc. etc