The Netcraft Web Server Survey is a survey of Web Server software usage on Internet connected computers. They collect and collate as

many hostnames providing an http service as they can find, and systematically poll each one with an HTTP request for the server name.

In August they received responses from 19,823,296 sites.

This month, Apache continues its lead at the top of the Web Server survey, although both it and Microsoft's IIS lost a bit of ground to the up and coming Zeus webserver, which is gaining popularity with bigger e-commerce sites like Ebay.

Linux also remains the mostly widely used Operating System to host web pages off, serving 35.73% of all websites compared with Microsofts(all flavors of windows) 21.32% or Sun's Solaris operating system which hosts about 20.35% of all sites on the Internet.

If you're interested in just how Netcraft compiles these statistics, you can read about their methodology for yourself.