What is WSS and MOSS?

Microsoft has divided SharePoint products into two parts. One is called WSS (Windows SharePoint Services) and the other is MOSS (Microsoft Office SharePoint Server). WSS is the platform in which MOSS is built. The WSS part is licensed through Windows 2003 Server and it does not cost anything. MOSS is a separate product by itself and needs licensing and it has a significant cost. WSS is good for small teams and small projects. MOSS has extra functionalities, in other words, Value Added Services. So the choice between WSS and MOSS will depend on the budget of the project and the VAS provided by MOSS.

How does WSS actually work?

WSS does not work in an isolated fashion. It needs help from two more products: IIS (Internet Information Server) and SQL Server.

How does WSS work with IIS?

In order to understand how WSS works with IIS, we need to first understand the concept of HttpHandlers and HttpModules. If you are not aware of this, you can refresh about them here.
Using HttpHandlers and HttpModules, a request is first passed through the SharePoint runtime and then passed to the ASP.NET runtime (aspnet_isapi.dll).

If you open the web.config file of a WSS enabled IIS web application, you can see the application runtime handlers and modules.

<httpHandlers>
<add verb="GET,HEAD,POST" path="*" 
   type="Microsoft.SharePoint.ApplicationRuntime.SPHttpHandler, Microsoft.SharePoint, 
         Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
</httpHandlers>

We have highlighted the application runtime module.

<httpModules>
<add name="SPRequest" 
  type="Microsoft.SharePoint.ApplicationRuntime.SPRequestModule, 
        Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, 
        PublicKeyToken=71e9bce111e9429c" />
</httpModules>