Web Dynpro for ABAP - how does it work

Will Web Dynpro for ABAP work the same as BSPs? - namely be a server side application - as opposed to Web Dynpro for Java which could be condsidered a "client" side application - well you can deploy the code to the portal WAS 6.40 and access the backend R3.

If it can be resident on the portal I assume that you have to install both the ABAP and Java stack on the portal WAS 6.40.

Is a Web Dynpro for ABAP application better performing than a corresponding BSP application?

Thanks

Patrick