Release 5U1 Message Queue is a maintenance release that fixes bugs in Release 5 Message Queue. Release 5 Message Queue was a feature release that represented a minor upgrade with respect to Release 4.
Message Queue software has historically included two editions, a Platform Edition and an Enterprise Edition, each corresponding to a different feature set and licensed capacity. Enterprise Edition was for deploying and running messaging applications in an enterprise production environment. Platform Edition was mainly for developing, and debugging messaging applications and components. With Release 5 Message Queue, the Platform Edition was deprecated and Message Queue includes all Enterprise Edition features. An upgrade from an earlier Java ES version to Java ES 5 converts any installed Platform Edition to full Message Queue enterprise-level features.