Phoenix Software International built JES3plus specifically to solve a problem IBM created: back in 2019, IBM announced that z/OS V2R5 would be the last release to support JES3, its Job Entry Subsystem for managing batch workloads on mainframes. That left JES3 shops with an uncomfortable choice — undertake a costly, risky conversion to JES2, or keep running an increasingly unsupported subsystem.
JES3plus, a licensed derivative of IBM’s own JES3 source code, is Phoenix’s answer: a plug-compatible replacement that lets clients keep everything they’ve already built around JES3 — user exits, source modifications, operator commands, JCL, production control procedures, NJE and RJP partner setups — without rewriting any of it. Value shows up in a few concrete ways.
First
The first is avoided migration cost and risk. Converting to JES2 is a major project, and Phoenix cites at least one financial institution whose calculated ROI on that conversion would have taken 25 years to pay back. JES3plus sidesteps that entirely, and clients report the switch to JES3plus itself is close to invisible operationally — comparable to installing a normal IBM JES3 maintenance release, with one major client saying “no one noticed anything had changed” after cutover.
Second
The second is that it doesn’t just freeze JES3 in place — it keeps improving it. Phoenix has shipped real performance work, including SPOOL I/O enhancements (support for zHPF, PAV, extended addressing) that in their benchmarks nearly doubled job throughput while cutting channel utilization by roughly 92%. They’ve also layered in modern capabilities IBM’s JES3 never got, like z/OSMF integration and enhanced WLM balancing, through ongoing annual releases.
Third
The third is preserving JES3’s distinctive architecture — things like multisystem coupling, intelligent tape sharing, workload balancing, and deadline scheduling, which are meaningfully different from how JES2 handles the same problems and which many long-time JES3 shops built their operations around.
Put Together
Put together, the pitch to mission-critical IBM Z customers is: keep the JES3 architecture and behavior you depend on, get a vendor actually committed to supporting and enhancing it going forward (with no end-of-life on the horizon), and avoid the cost and disruption of a forced platform conversion.