What is Tomcat? Is it a Web Server? What can Tomcat do? How is it different than Apache Web Server? As it was a bit confusing for me, I made a small research on these and wanted to share some notes here. What we should keep in mind from this answer is: In general, the Apache HTTP server is just a plain old web server designed to serve static web pages. There are plenty of modules which can be installed to enhance Apache's abilities so that it can serve dynamic webpages using various technologies such as PHP, CGI or whatever, but the core of Apache is just a plain old HTTP server. I think rest of the answer is not very clear, the part explaining what Tomcat actually is so let's move on to some other resources.. Even the question itself starts with good information: I know that Tomcat is written in Java and the HTTP Server is in C, but other than that I do not really know how they are distinguished. Do they have different functionality? And a comment in the accepted answer gives us a lot of nice information: Tomcat does indeed bring with it a capable web server. Tomcat is a Servlet/JSP container and also offers a web server. Tomcat's web server is quite good, able to handle most small and medium web site needs. With support for Java NIO and 64-bit memory, even some larger scale web sites may be served well by Tomcat's Catalina module. For various reasons, some folks choose to ignore Coyote and instead use Tomcat's Servlet capabilities behind the Apache httpd web server product. Tomcat = ( Web Server + Servlet container + JSP environment ). The web server is ON by default when you run Tomcat’s startup.sh script, listening on port 8080 for incoming connections (HTTP calls). Tomcat is pure Java, with its own web server implementation (Coyote). The Apache HTTP Server (AHS), in contrast, has a completely separate implementation of a web server, using native C/C++ code. AHS is very flexible and powerful, but is often overkill. Tomcat's own web server works very well. Use AHS only if truly needed. This gives us the hint that Tomcat actually is a collection of a few modules. Components Tomcat 4.x was released with Catalina (a servlet container), Coyote (an HTTP connector) and Jasper (a JSP engine). Catalina Catalina is Tomcat's servlet container. Catalina implements Sun Microsystems' specifications for servlet and JavaServer Pages (JSP). In Tomcat, a Realm element represents a "database" of usernames, passwords, and roles (similar to Unix groups) assigned to those users.Different implementations of Realm allow Catalina to be integrated into environments where such authentication information is already being created and maintained, and then use that information to implement Container Managed Security as described in the Servlet Specification. Coyote Coyote is a Connector component for Tomcat that supports the HTTP 1.1 protocol as a web server. This allows Catalina, nominally a Java Servlet or JSP container, to also act as a plain web server that serves local files as HTTP documents. Coyote listens for incoming connections to the server on a specific TCP port and forwards the request to the Tomcat Engine to process the request and send back a response to the requesting client. Another Coyote Connector, Coyote JK, listens similarly but instead forwards its requests to another web server, such as Apache, using the JK protocol.This usually offers better performance. Jasper Jasper is Tomcat's JSP Engine. Jasper parses JSP files to compile them into Java code as servlets (that can be handled by Catalina). At runtime, Jasper detects changes to JSP files and recompiles them. The information I find here particularly important is: Apache Tomcat and Apache HTTP are completely different server technologies. It is impossible to use a plugin for Apache HTTP server with Tomcat. Apache HTTP server is developed in C and so are the plug-ins. On the contrary Tomcat is now completely developed in Java. Tomcat doesn't only serve static content, but it can also serve JSP pages and servlets. In this post I tried to summarize the knowledge I have found around. This will help me remember this information whenever I need it, and hopefully is useful for you as well. Courtesy: Koray Tugay

What is Tomcat? Is it a Web Server? What can Tomcat do? How is it different than Apache Web Server?

As it was a bit confusing for me, I made a small research on these and wanted to share some notes here.

What we should keep in mind from this answer is:

In general, the Apache HTTP server is just a plain old web server designed to serve static web pages. There are plenty of modules which can be installed to enhance Apache's abilities so that it can serve dynamic webpages using various technologies such as PHP, CGI or whatever, but the core of Apache is just a plain old HTTP server.

I think rest of the answer is not very clear, the part explaining what Tomcat actually is so let's move on to some other resources.. 

Even the question itself starts with good information:

 I know that Tomcat is written in Java and the HTTP Server is in C, but other than that I do not really know how they are distinguished. Do they have different functionality?

And a comment in the accepted answer gives us a lot of nice information:

Tomcat does indeed bring with it a capable web server. Tomcat is a Servlet/JSP container and also offers a web server. Tomcat's web server is quite good, able to handle most small and medium web site needs. With support for Java NIO and 64-bit memory, even some larger scale web sites may be served well by Tomcat's Catalina module. For various reasons, some folks choose to ignore Coyote and instead use Tomcat's Servlet capabilities behind the Apache httpd web server product.

Tomcat = ( Web Server + Servlet container + JSP environment ). The web server is ON by default when you run Tomcat’s startup.sh script, listening on port 8080 for incoming connections (HTTP calls). Tomcat is pure Java, with its own web server implementation (Coyote). The Apache HTTP Server (AHS), in contrast, has a completely separate implementation of a web server, using native C/C++ code. AHS is very flexible and powerful, but is often overkill. Tomcat's own web server works very well. Use AHS only if truly needed. This gives us the hint that Tomcat actually is a collection of a few modules.

Components

Tomcat 4.x was released with Catalina (a servlet container), Coyote (an HTTP connector) and Jasper (a JSP engine).

Catalina

Catalina is Tomcat's servlet container. Catalina implements Sun Microsystems' specifications for servlet and JavaServer Pages (JSP). In Tomcat, a Realm element represents a "database" of usernames, passwords, and roles (similar to Unix groups) assigned to those users.Different implementations of Realm allow Catalina to be integrated into environments where such authentication information is already being created and maintained, and then use that information to implement Container Managed Security as described in the Servlet Specification.

Coyote

Coyote is a Connector component for Tomcat that supports the HTTP 1.1 protocol as a web server. This allows Catalina, nominally a Java Servlet or JSP container, to also act as a plain web server that serves local files as HTTP documents.

Coyote listens for incoming connections to the server on a specific TCP port and forwards the request to the Tomcat Engine to process the request and send back a response to the requesting client. Another Coyote Connector, Coyote JK, listens similarly but instead forwards its requests to another web server, such as Apache, using the JK protocol.This usually offers better performance.

Jasper

Jasper is Tomcat's JSP Engine. Jasper parses JSP files to compile them into Java code as servlets (that can be handled by Catalina). At runtime, Jasper detects changes to JSP files and recompiles them.

The information I find here particularly important is:  

Apache Tomcat and Apache HTTP are completely different server technologies. It is impossible to use a plugin for Apache HTTP server with Tomcat.
Apache HTTP server is developed in C and so are the plug-ins. On the contrary Tomcat is now completely developed in Java. Tomcat doesn't only serve static content, but it can also serve JSP pages and servlets.

In this post I tried to summarize the knowledge I have found around. This will help me remember this information whenever I need it, and hopefully is useful for you as well.

Courtesy: Koray Tugay