2 tier architecture is nothing but client and server
Means It consits of client(Presentation layer) and server
(may be database)
Client gives the requests through the browser for HTMl
pages stored in remoting machine(Server).The server locates
this files and passes to the Client
Only presentation layer and database server exits
Request are in the form of Http or FTP
Most of the actions done on the client side so client is
thick and server is thin
Web application consits of Presentation layer( client or
browser)Business process and database layer
As i mentioned earlier
Presentaion layer is useful for to submit the requests in
HTTP form
Web server recieves the Request in HTTP form and sends to
application server. Application server process the Request
and gets the information from the database and sends back
to Web server. WEb server sends the recived data in the
form of HTML to the client.
Most of the action done on the server side
so client is thin
Presentaion laye<-->web server<-->application server<-->data  |