What is the difference between CGI and servlets?

In traditional CGI, a new process is started with each client request and this will correspond to initiating a heavy OS level process each time when a client request comes. While in case of servlets JVM handles client requests at a web server end and each client request correspond to thread which consumes less resources as compared with CGI process, thus making CGI inefficient. In Java servlet, there is only a single instance, which answers all requests concurrently. This saves memory and allows a Servlet to easily manage persistent data.Java servlets resides in Servlet engine and are executed within sandbox making it more secure and robust.