JBoss Messaging was designed and built from the ground up and was not based on the JBoss MQ architecture and is 100% JMS Compliant
The main new features are related to clustering functionality. JBoss Messaging contains a fully functioning and highly scalable clustering implementation. Unlike JBoss MQ, JBoss Messaging does not rely on a "HA Singleton", this was a major drawback in JBoss MQ, where only one JMS server in the cluster was active at any one time, providing a scalability bottleneck. With JBoss Messaging this limitation disappears and all nodes in the cluster can simultaneously host active JMS servers allowing the load to be distributed much more smoothly.