A VirtualDirectory? under MicroSoft InternetInformationServer made up one or more ActiveServerPages, with a single configuration.
Each AspApplication can be configured independently within MicroSoft InternetInformationServer.
Configuration settings include:
The ASP IsapiExtension is completely configurable per AspApplication. Check out the following article at http://msdn.microsoft.com/workshop/server/feature/tune.asp for more details on what IisMetaBase settings to use to configure it. (Note: You'll need to scroll down to the section titled "Optimizing Active Server Pages (ASP) Performance".)
See also: ActiveServerPages