n-Tier environment ... design

One of the biggest differences, at least in terms of perspective, between a Win32 application (aka Fat Client) and a web browser application is that the Win32 application is used by a single person whereas the web application may be used by hundreds, or thousands of people at one time.  OK, quiet down out there, let me explain.

A Win32 application is run on a desktop and is run by a single person at a time.  The application may be installed on hundreds or thousands of machines, but each machine has a single person running the application.  In this manner the workload is distributed between each workstation and the database server.  In a web based application all of that processing needs to occur somewhere.  While some of it happens on the browser, a good portion of it runs on the web server.  Therein lies the problem.

Many web applications are built in such a manner that they consume large amounts of CPU and memory in order to serve a single client.  Multiply by the number of people that are going to be accessing the application and you have a nightmare on your hands. Many years ago servers used to be much more powerful than desktops.  This was due to the advance architecture used in the servers and the very expensive chips used.  As prices have dropped, however, this distinction has almost completely disappeared.  Indeed, a new desktop may, in some circumstances, be faster than the server to which it is communicating.  Because the average developer has a fairly powerful machine, what seems to run quickly on their desktop completely bogs down on the server when multiple people try to access it.

Our current Production servers are quite large and contain a lot of raw horsepower.  We do not have a large number of concurrent users.  I would personally be surprised if we hit 40 on any one server.  This is in comparison to a server at Google that is designed to support hundreds of concurrent users.  On-line games, such as World of Warcraft, support thousands of concurrent users.  While we don't need to write our applications so that we can support thousands of concurrent users, we should always be cognizant of the fact that our application does not operate alone.  It needs to co-exist with itself and others.