Drivers for an n-tier architecture solution pattern include:

• The web and application servers will usually scale at different rates, with the web server being able to handle more concurrent users than the application server.
• If the web and application servers are bound together, failure of a web server will result in no requests being delivered to the associated application server.
• Application server software licenses tend to cost more money than web server software, and these licenses are usually on a per processor basis, so more hardware servers running the application server will cost more money regardless of whether that capacity is used or not.
• It is hard to optimize a hardware server for both memory-intensive computation and disk or network I/O.
• Only a small amount of the response returned to the user may involve application server functionality.