When I told people I was writing a book called Web Performance Tuning, the usual response I got was that the title should be "Web Server Performance Tuning." Most people believe that the server is the only part of the Web that you can tune. When you're desperate to improve performance, however, you become much more creative about finding other parts of the Web that you can tune. You may not be able to do much about the public network or about remote clients, but you can tune entire intranet systems, including clients, networks, servers, and databases, and you can improve your access to the public network through better connections and strategic locations for clients and servers. Yes, you can tune the web server itself, but the server is only one piece.
Thinking in terms of individual machines is rapidly becoming obsolete. An isolated machine, whether PC or mainframe, is increasingly rare. There is a very good reason for this: a collection of machines is far more powerful, flexible, and reliable than any individual machine. The network takes on the characteristics of a bus connecting the components of a larger and better computer. To have a network connection to another machine is to have more power available from your own machine. To be connected to the Internet is to have access to millions of machines. The biggest disk in the world is simply all disks wired together.