JServ ：

one of the very first servlet engines（比较老的容器了）. It is now an open source project, consisting of two parts: a pure-java servlet engine, compliant with the Servlet spec version 2.0, and an Apache module written in C called mod_jserv that allows Apache to send servlet requests to the JServ JVM.

Tomcat：

a completely separate product, originally written by Sun, that is now also open-source and administered by Apache. It supports the Servlet spec version 2.2, and the JSP spec version 1.1. It also contains a pure Java servlet engine, and a number of connectors for several commercial web servers.

下面就是讲述mod_jserv和mod_jk的演变：

大致意思是，mod_jserv是 Jserv用来和Apache做连接的，tmocat也想搞一个，用来和Apache连接，本来打算那mod_jserv改改，重新写写，但是写了一段时间后发现，还是不行，最后干脆重新自己写个新的吧，就叫mod_jk，这个新的就是tomcat拿来和Apache 连接用的。功能还不错，支持SSL。。。

Here's the confusing part: originally, when it was time to write a connector from Apache to Tomcat, they started with the code base of mod_jserv. Although it has been rewritten and revised to the point where it is no longer compatible with the mod_jserv that comes with JServ, unfortunately, it is still called mod_jserv. This means that if you have the JServ mod_jserv installed, it will no twork with Tomcat, and vice versa（反之，也是如此）.

So if you just use mod_jk and Tomcat, you should have no problems (at least as far as this connector issue is concerned).