Answer
Servlet Engines are a Java platform technology for extending servlets. All Servlet Engines have a common API. The Servlet Connector component of ArcIMS requires a Servlet Engine if your Web server does not support servlets natively.
Java Servlet technology provides Web developers with a simple, consistent mechanism for extending the functionality of a Web server and for accessing existing business systems.
Servlets provide a component-based, platform-independent method for building Web-based applications.
For information on supported Web servers and servlet engines, see the link in Related Information below.